Radiography of Acute Appendicitis
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Looks at how different radiology modalities such as diagnostic imaging, CT and Ultrasound evaluate RLQ abdominal pain. Acute abdomen pain is evaluated in several radiology subspecialties. Appendicitis is most commonly evaluated by CT and ultrasound.
Author: Nicholas Joseph
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Why should radiographers have a discussion about acute appendicitis and imaging of the Appendix? This discussion is very important because acute appendicitis is one of the most common surgical emergencies seen in the United States. Over 250,000 appendectomies are performed annually. In many of these cases some form of radiographic imaging was necessary to sort through the various differentials in non-classical cases before diagnosing appendicitis. In terms of cost to explore nonclassical differentials medical imaging is an effective economical way to reduce overall medical cost. The American College of Radiology (ACR) recommends physicians use appropriateness criteria in evaluating acute right lower quadrant abdominal pain. Radiology imaging may include plain films, computed tomography (CT), and/or graded compression ultrasonography. CT is the preferred tool and is highly recommended when dealing with nonclassical presentations of appendicitis especially in those patients who are obese, or have a rigid noncompressible abdomen, or may have complicated appendicitis such as rupture with abscess. Improvements in imaging equipment and the emergence of good imaging criteria have provided clinical physicians concrete radiological tools in the fight to reduce the morbidity and mortality caused by acute appendicitis. ACR recommendations have moved radiology procedures into mainstream medical practice assisting emergency and surgical response to acute appendicitis. ACR recommendations are strengthen by reviews that include real time and retrospective imaging studies. Radiographic imaging of the appendix is highly specific and sensitive for evaluating abdomen pain.
When properly performed, imaging for appendicitis using ionizing radiation is in keeping with the practice ALARA (As Low As Reasonably Achievable) radiation dose for all patients, especially the young, and during pregnancy. Notwithstanding the need to get an accurate diagnosis speedily and commence treatment in cases where appendicitis is found remains a clear basis for “risk vs. benefit” imaging for all age groups. An example of how we apply radiation control and ALARA can be seen in the results of various studies that conclude CT may be far superior to ultrasonography (US) in the detection of acute appendicitis in adults, while ultrasound may be the best choice in young children and women of childbearing age, or during pregnancy because no radiation is used. Medical literature points to computed tomography as an excellent tool having excellent diagnostic accuracy for diagnosing appendicitis in adolescents, adults, and the elderly. When a diagnosis of appendicitis cannot be confirmed by clinical and laboratory data alone, the use of CT is medically supported in all obscure presentations of RLQ abdominal pain. As any good clinician knows it is imperative that an early clinical evaluation occurs at first suspicion of acute appendicitis. If confirmed quickly medical and or surgical intervention reduces morbidity and mortality. This approach is effective even during pregnancy or when the patient is young. Yet in real practice the urgency of immediate diagnosis is likely to be compromised when the patient’s presentation confounds the clinician with many differentials. They must all be sorted through before confirming the diagnosis of acute appendicitis to avoid unnecessary surgical intervention. In addition, neither routine laboratory test or radiology procedures have sufficient specificity and sensitivity to diagnosis all the clinical presentations of right lower quadrant abdominal pain and its differentials. When facing a battery of diagnostic tests a good patient history, physical examination, laboratory testing, and radiological evaluation may be needed to narrow those differentials close to appendicitis and conclude appendicitis. Therefore, the current standards for acute right lower quadrant (RLQ) pain conclude that imaging test should be commonly used to improve diagnostic accuracy in cases that may require early surgical intervention. The goal of radiologic imaging is to improve the number of true positive and decrease the number of false-negatives and false positives that have confounded medical practice. Our discussion of imaging acute appendicitis will review those imaging techniques and practices used in general diagnostic imaging, CT, ultrasound, and nuclear medicine. Currently, diagnostic imaging using magnetic resonance imaging (MRI) and nuclear medicine (NM) for appendicitis is not routine and is not explored in this material.
1.1 Anatomy of the Appendix
Laypersons and anatomists alike have raised the questions, “just what is the appendix, and what is its function?” This debate continues to this date as anatomists are still trying to determine the exact role of the appendix. While no conclusions have been reached several interesting observations continue to fuel studies for the debate. In most people the appendix is anatomically attached to the posterior aspect of the cecum; the cecum is the first part of the large intestine. Proximal to where the appendix attaches the terminal ileum of the small intestine joins the cecum. At this junction the ileocecal valve regulates entry of chyme into the colon. The appendix has its own mesentery called the meso-appendix, a feature that helps distinguish it from the cecum, which has no mesentery. The appendicular artery is the main supplier of oxygen and nutrient rich blood to the appendix. It extends through the meso-appendix reaching various parts of the appendix. An accessory artery can branch from the ileocolic or posterior cecal artery to partially supply the appendix.
Left radiograph shows a barium filled cecum and appendix. In most people the appendix buds from the posteromedial wall of the cecum just slightly below the ileocecal valve. The radiograph on the right is a mesenteric arteriogram demonstrating the rich blood supply that spreads through the mesentery to supply the bowel and appendix. Appendicular and ileocolic arteries branches supply the appendix from the inferior mesenteric artery (arrow).
The drawing on the right demonstrates the location of the appendix, meso-appendix, and arterial supply in relation to the large intestine. The radiograph on the left is a mesenteric arteriogram that shows the rich arterial supply to the gut.
The vermiform appendix as its name implies is a narrow worm-shaped tube attached to the cecum approximately 2-3 cm below the ileocecal junction. It may be from 5 cm to up to 20 cm in length, but averages about 8 cm. It is surprisingly longer in infants and children giving the impression that it may be functional in this age group. A normal diameter for the appendix in adults is less than 6mm. Being a closed tube distally, it may swell quickly when in a diseased inflamed state.
These are two axial CT slices through the pelvic region showing the terminal ileum and cecum (image A) which is superior the appendix. CT image “B” is distal to the ileocecal junction. It shows a swollen appendix due to acute appendicitis. The appendix is easier to see because it is fluid filled. This axial slice also demonstrates the location of the appendix, which is posteromedial in this patient and about 2.5 cm below the ileocecal junction.
Not surprisingly the appendix can vary in how it buds from the cecum. In approximately 64% of the population it is found posterior to the cecum (retrocecal) within the retrocecal recess. The retrocecal recess is formed by peritoneum that envelops the cecum fusing it to the iliac fossa. The appendix is commonly found posterior to the ascending colon (retrocolic), or close to the ovary or ureter, and if long enough deep within the pelvis. The retrocecal recess is generally deep enough for a surgeon to slip a finger into to remove the appendix. The root of the appendix lies deep to what surgeons call McBurney’s point. This point can be found by drawing a line from the anterior superior iliac spine (ASIS) to the umbilicus. McBurney’s point is found at the lateral third of this line, which is where severe pain caused by acute appendicitis is frequently described.
This drawing demonstrates the location of McBurney’s point, which can be found along a line drawn from the umbilicus to the anterior superior iliac spine (ASIS). The point is found at the lateral third of this line. This is a location where RLQ pain is commonly reported by patients with acute appendicitis.
Note the positions of the appendix in these different individuals with acute appendicitis. In CT image A the appendix buds medially from the cecum; the position of the appendix on CT image B is close to the lateral wall (white arrows).
Many anatomists believe that the appendix is a rudimentary structure of the bowel and has no function in man. Others tend to disagree because the vermiform appendix in infants and children is well formed and has the histological appearance of a well-developed lymphoid organ. This has led to the belief that it may yet have important immunological functions that are still undiscovered. Clearly it has not been shown to have digestive functions in man. Histologically its layers do conformed to that of the large intestine having a mucosa, lamina propria, submucosa, and muscularis. It does have some secretory functions. It has been shown to produce mucinous secretions into its lumen like the rest of the gut. By far the characteristic feature of appendicular tissue is its masses of aggregated lymphoid tissue and lymphocytes scattered throughout the mucosa and submucosa layers. These aggregate lymphocytes, scattered lymphocytes, and lymphoid follicles are abundantly seen in its layers. For this reason many anatomists are reluctant to give way to the belief that it is totally a rudimentary structure in humans. The small pencil size opening into the appendix often closes in adults by the age of 40 adding to the belief it is undeveloped. Consider the histology of the normal appendix. From the lumen outward its layers are the mucosa, lamina propria, submucosa, muscularis, and adventitia. There are no digestive glands or secretory ducts within these layers to suggest digestive enzyme production or function. But these many organized lymphoid aggregations do suggest an immune role for the appendix. Ironically, these lymphocytes may account for the profound inflammatory changes seen with acute appendicitis. This debate over its function will no doubt continue for many years. However, all agree that the removal of the appendix does not seem to present any functional loss for the individual's digestive or immune systems.
This histological transverse section through the appendix and labeled magnified view shows diffusely scattered masses of lymphoid tissue throughout the lamina propria (LP). Scattered infiltrates within the submucosa (SM) and to a lesser degree in the muscularis layer suggest immune function. In spite of these rich lymphoid aggregations within the appendix no specific function has yet been ascribed to it.
1.2 What is Appendicitis?
Appendicitis can be a confusing term because it has a complex cycle of events that occur before the clinical symptoms of appendicitis are apparent. In simple terms, appendicitis can be defined as inflammation or infection of the appendix. It holds special importance in medicine because it is the most common acute surgical emergency of the abdomen. Most frequently affected are males, which have an incidence of about 57% and for women the incidence is about 43%. Appendicitis usually affects adolescents and young adults of both genders, and can occur at any age. However, most victims of appendicitis are between 15 and 44 years of age. It is believed that the way acute appendicitis begins is that somehow a blockage of the appendiceal lumen occurs. This prevailing belief was proven many years ago through experimental scientific means by Wangensteen and published in the Annual of Surgery, 1939.
This inflamed appendix specimen from an appendectomy shows swelling and areas of necrotic formation. This is the result of the cyclic changes of bacterial invasion, intraluminal pressure, and ischemia (Picture provided as a courtesy of the pathology department - Regions Hospital, St. Paul, Minnesota).
Among the most common causes of appendicular luminal obstruction are thicken mucus, feces (fecalith), calculus, tumor, or a worm ball (exyuriasis vermicularis) that becomes hardened and can be seen as a structure called an appendicolith. This blockage is bad for the appendix because its normal physiological secretion of a mucinous fluid by the mucosa into its lumen can cause swelling. A blockage of the lumen by an appendicolith causes these secretions to build up soon filling the small appendicular lumen resulting in a subsequent rise in intraluminal pressure. Rising intraluminal pressure causes a sequeal of events that include compression of its draining veins. They soon collapse under pressure as poor to absent drainage ensues. These dynamic cyclic changes lead to ischemia of the appendix. Such conditions favor bacterial invasion into its wall setting the stage for inflammatory changes to develop. Inflammation is part of those cyclic changes that promotes ongoing edema and exudation causing more swelling. As swelling continues the draining veins of the appendix become even more compressed further acerbating that situation. All of these changes are cyclic and once these cyclic changes ensue the situation is acerbated by greater bacterial invasion, more ischemic injury and inflammation, greater swelling, until symptoms of appendicitis are seen clinically and the risk of rupture greatly increases.
An untreated rupture of the appendix carries a high risk for fatality. The treated case-fatality rate for appendicitis is about one percent for nonperforated appendicitis and leaps to higher than 5 percent when perforation occurs.
A ruptured appendix is a life threatening condition that must be treated as an emergency. When the appendix ruptures it may form an abscess that can be seen radiographically; this is a key indicator of appendicitis. Unlike 40 years ago, medical treatments are generally successful in treating appendicitis and the consequences should it rupture. However, early diagnosis and treatment is paramount to avoid serious complications that may include long hospitalization or even death. For most appendicitis suffers the hospitalization is less than 4 days when no complication occur. Late diagnosis and treatment may cause the spread of inflammation throughout the abdomen, a condition known as peritonitis, which is a severe medical condition. For this reason, as radiographers we should be familiar with the imaging of the appendix and its consequences for those suffering appendicitis so we can properly expedite imaging requests.
These three axial CT slices (radiographs A, B, and C above) demonstrates an inflamed fluid filled appendix. All three CT images show an appendicolith blocking the lumen at its junction to the cecum (arrows). There is a significant amount of swelling of the appendix as a result of this blockage due to cyclic changes of edema, ischemia, and bacterial invasion. The appendicoliths, wall enhancement with surrounding infiltrate is consistent with a diagnosis of appendicitis.
These two pictures demonstrate changes within the appendix that causes acute appendicitis. The picture on the left shows a swollen appendix attached to the cecum. Note the stress on the blood vessels caused by the swelling. The picture on the right is a cross section through the appendix showing an appendicolith blocking the lumen. Blockage of the lumen is one of the most common causes of acute appendicitis.
There are mechanisms other than blockage of the appendicular lumen that can cause appendicitis, but these are still poorly understood. A significant but small incidence of inflamed appendicitis occurs without luminal obstruction or appendicolith. These findings are not fully explained in our current medical knowledge, but are not totally idiopathic. The submucosa undergoes hyperplasia in nearly 60% of these cases. An alternate theory is that the appendix ruptures (for reasons unknown) as the first stage in appendicitis. This causes a seeding of bacteria into the abdomen, which is generally limited to a local area around the appendix and cecum forming a periappendiceal abscess. Sometimes this can be seen with a CT scan or with ultrasound. Small abscess following surgical removal of the appendix can be treated with percutaneous placed indwelling catheter drainage. In such cases the CT scan can be performed following surgery and a drainage tube immediately placed.
1.3 Clinical Symptoms of Acute Appendicitis
The etiology of clinically acute nonspecific appendicitis (the most common diagnosis made in this organ) remains enigmatic even though the appendix is a commonly examined and resected intraabdominal organ. Acute appendicitis has classical symptoms that are well known to physicians. Symptoms tend to follow a know sequence that begins with periubilical pain that soon localizes to the RLQ. This may be followed by nausea and/or vomiting and abdominal tenderness over McBurney’s point. Victims will have rebound tenderness, possibly mild fever initially that may increase with progression of symptoms or rupture of the appendix. Laboratory signs may include an elevation in the peripheral white blood count to greater than 10,000 mm3 and often exceeds 15,000 mm3. Some individuals experience weakness and may become diaphoretic, show pallor, and possibly shock. As inflammation progresses the abdomen may become distended and paralytic ileus becomes a factor. Bear in mind that this is the classical presentation of acute appendicitis, but is infrequently seen leaving a myriad of differentials to be sorted. Even if these signs are present the physician must sort all differentials before a correct diagnosis is made since there are other conditions that can closely mimic appendicitis.
Acute appendicitis is known for its sudden onset, most victims are seemingly quite well just an hour or two before clinical symptoms emerge. As a young man of 17 years age, I was returning from school one afternoon I seemed perfectly fine when I left school. But by the time I arrived at home just an hour later I was febrile, disoriented, and writhing in pain. The diagnosis of acute appendicitis was made at a local emergency room just 2 hours after the sudden attack. In approximately 90% of those with classical symptoms there will be increased white blood count (WBC) and slight rise in temperature (about 100-101 degrees Fahrenheit, or 38 degrees Celsius). Diagnostic testing is required in many cases because only 50-55% of appendicitis cases present with classical signs. If early diagnosis is not made, then inflammation advances producing gangrene, making rupture likely. Just before rupture advanced inflammation in the mesentery or peritoneum may produce an area of hyperesthetic skin over the appendix. The physician may test for hyperesthetic skin by clasping skin with the index finger and thumb over the affected area. Then pulling it upward will elicit the proverbial pain expressions in those with inflammation beneath. When there is a positive skin response the patient may be at a critical state and should be treated immediately before life-threatening consequences of rupture can occur. Because many times appendicitis presents with less defined clinical symptoms patients must undergo diagnostic testing to confirm the correct diagnosis. The clinician must rule out differential causes of acute abdominal pain that include renal stone, diverticulitis, colitis, ovarian cyst, and many others. It can be more difficult to clinically detect acute appendicitis in certain patients. Some examples are those that are immunocompromised, organ transplant recipients, and those receiving prophylactic treatment of HIV. Those undergoing cancer immunosuppressive therapy and chemotherapy can have masked symptoms. These patients present special challenges to physicians when inflammatory conditions are clinically suppressed. Also populations like very young individuals, the elderly, and pregnancy can make acute appendicitis especially difficult to diagnose as a single cause of acute abdomen pain.
When classical signs are absent the differentials may include mesenteric lympodenitis, enterocolitis, ectopic pregnancy, enterocolitis, biliary colic, regional ileitis, Meckel’s diverticulitis, pregnancy, acute salinities, and even mittelschmerz to name a few. Immediate diagnosis of appendicitis can be quite elusive. During the clinical examination the physician looks for abdominal wall guarding and rebound tenderness (called peritoneal signs). When there is inflammation of the peritoneum the patient’s abdominal muscles may be tensed in anticipation of touch (guarding). On physical examination the physician may flex the hip or internally rotate it to elicit the obturator sign. The technique of moving the psoas muscle causes of the Obturator sign. Other manipulations include palpation of the left side of the abdomen, which may cause pain on the right side (Rovsing’s sign); however, the clearest palpatible sign of appendicitis is rebound pain when pressure is applied to McBurney’s point. It is a characteristic signature pain caused by pressing down over the appendix. There should be less pain when pressing down over McBurney’s point than experienced when the hand is quickly removed allowing it to rebound. Sometimes the pain is not localized over the expected location because of the various possible locations of the appendix as we have discussed. For example, a retrocecal appendix with appendicitis may present with pain in the right flank (area between the ribs and iliac crest) just as does renal stone pain, or a pelvic appendix may present with pain in the pelvis. These different locations of the appendix and different presentations of appendicitis often confound physicians requiring careful sorting of potential diagnostic differentials.
To understand how difficult it can be to differentiate causes of right lower quadrant (RLQ) abdominal pain let’s look at a case complicated by pregnancy. A 26-year old female presented to an emergency room complaining of acute RLQ pain that continued for greater than 8 hours. After evaluating other possible causes the physician was reasonable sure the pain was caused by acute appendicitis. The woman was about 34 weeks pregnant at the time. Because the patient was pregnant an ultrasound study was performed, the results inconclusive. Following consultation with the on duty radiologist a CT scan was performed. To reduce patient and fetal dose the scan noise index was raised and the milliamperage (MA) decreased. The scan results confirmed an appendicolith and abscess; the inflamed appendix was successfully removed. Here’s the question for thought, was her pregnancy at risk before diagnosis and surgery? ANSWER: Appendicitis during pregnancy is associated with increased risk to the mother and the fetus. There is also a higher risk of fetal loss when emergent appendectomy is performed during pregnancy. This is especially the case in early pregnancy or when the appendicitis is complicated by appendiceal perforation. Despite the difficulty of diagnosing appendicitis during pregnancy, a CT scan may be necessary because of the risk associated with rupture. When a positive diagnosis of appendicitis is found appendectomy should not be delayed.
Now let’s look at two CT images from the case just described. The images below demonstrate why it is necessary to image patients with nonclassical signs of appendicitis. The intrauterine gestation is seen along with an anterior placenta, acute appendicitis with appendicolith, and periappendiceal abscess. The risk to the fetus had the diagnosis not been made is rupture and complicated pregnancy that may have resulted in fetal loss. The point here is that often the symptoms of appendicitis are not classical and diagnostic imaging is the best approach to diagnosis, even during pregnancy.
This is a good case study to demonstrate the necessity of radiographic imaging to evaluate RLQ abdominal pain. In this case the obstetrician was highly suspicious of appendicitis and requested a CT scan to confirm the diagnosis. Risk of fetal loss is higher when complicated appendicitis like abscess formation is present. Pregnancy makes any clinical decision to use ionizing radiation difficult; however, the risk vs. benefit even warrants radiographic imaging. Differentials such as diverticulitis, ruptured diverticulosis, renal stone, and other causes of RLQ abdomen pain can be differentiated using radiographic imaging.
1.4 Diagnostic Tests to Evaluate for Appendicitis
Acute appendicitis may become a surgical emergency, whereas other causes of abdominal pain, such as renal stone or diverticulosis may not. Several radiological and laboratory tests may be performed to differentiate the cause of acute RLQ abdomen pain. Evaluation may include urine analysis, abdomen x-rays, ultrasound, barium enema, CT scan, or others the physician may deem necessary. A urine analysis can point to a possible renal stone or pelvic inflammation. The urine analysis may include a microscopic search for red blood cells, bacteria, or white blood cells that would suggest renal or bladder cause for pain. Studies show that diagnostic imaging and early interventional treatment of appendicitis can reduce morbidity, mortality, and postoperative hospitalization time. Diagnostic imaging studies that are commonly performed are:
Plain films of the abdomen, barium enema with fluoroscopy, CT, ultrasound, and nuclear medicine studies can play a role in evaluating abdomen pain. CT is a very good study and can be performed with or without oral and intravenous contrast agents. Ultrasound is very useful for diagnosing appendicitis in the young and during pregnancy because it uses no ionizing radiation. Radioisotope imaging with technetium (99m Tc) labeled white blood cells is being investigated in patients with acute appendicitis. As of July 2004, the United States Food and Drug Administration approved a new product, technetium (99m Tc) fanolesomab, which utilizes a monoclonal antibody to label WBCs. The product had high specificity for scintigraphic imaging of patients with equivocal signs and symptoms of appendicitis who are five years of age or older. However, the product was removed from the market in December 2005 pending results from continued research surrounding unacceptable adverse side effects.
Sometimes plain film x-rays are taken using a protocol called the acute abdominal series (AAS). This may include an upright chest, upright abdomen, and supine abdomen views. Plain films can help differentiate early bowel obstruction and on occasion may even show a fecalith within an inflamed appendix. Plain film radiographs provides a good survey about the patient’s abdomen. While studies show that plain films are generally noncontributory for appendicitis their low sensitivity may provide good general information about the abdomen. A recent study-evaluating 871 patients with abdominal pain had a nonspecific reading in 588 (68%) of 871 patients. The same study had normal findings in 200 (23%) patients, and some abnormal findings in 83 (10%). This same study concluded like most others that abdominal radiography had 0% sensitivity for appendicitis as a screening protocol, and likewise for other pathologies such as pyelonephritis, pancreatitis, and diverticulitis. The physician must consider all differentials and the best way to test for them when RLQ abdominal pain persists. But before we dismiss the AAS survey it should be noted that retrospective studies have shown an occasional mass effect or an appendicolith pointing to appendicitis on plain films. But the sensitivity for appendicitis is so low that plain films imaging specifically for appendicitis should not be performed.
De dombal conducted a larger study reviewing 10,682 patients with acute abdominal pain. This study recorded an incidence of 28% with appendicitis. Cholecystitis was found in 9.7%, 4.1% had small bowel obstruction, 4% had gynecologic disorders, 2.9% had pancreatitis, 2.9% had renal colic, 2.5% had peptic ulcer disease, 1.5% had cancer, 1.5% had diverticular disease, and 9% had a variety of other less common conditions. The study concluded that a specific diagnosis for plain film imaging was not found in 34% of cases that had plain film imaging as part of the work-up. This data does not suggest that plain film radiography has no value in diagnosing acute abdominal pain. In fact, plain film radiography has great diagnostic value in abdominal imaging when appropriately applied. Sometimes plain films can show signs of bowel obstruction, renal stones, fecaliths, gallstones, diverticulitis, colitis, and many others, but is not specific for any of these conditions.
The question that seems to always confront medical practitioners is what is the value of traditional abdominal radiography in emergency diagnosis of acute abdominal pain? Studies show that AAS interpretations have an overall sensitivity, specificity, and accuracy of 30%, 88%, and 56% respectively. Comparing this data to unenhanced CT of the abdomen that has overall sensitivity, specificity, and accuracy of greater than 95% it fails to persuade its use. Consider the following examples of how the acute abdominal series has helped in initial screening of nontraumatic acute abdominal pain.
This upright abdomen plain film radiograph shows air-fluid levels in a young patient suspected of appendicitis or small bowel obstruction. No mass effect or appendicolith is seen in the area of the appendix. This radiograph did not exclude appendicitis, but did provide insight to possible cause of the patient’s abdomen pain.
This is a supine radiograph taken of a different patient whose chief complaint was severe right lower abdomen pain. Note the bone lesions involving the right hip, which may be a cause of the patient’s ongoing pain. This is another example of a plain film taken for abdomen pain in which appendicitis was in the differential but had low probability. Plain films can be useful for evaluating other causes of acute and chronic abdomen pain, even when they do not exclude appendicitis.
This partial upright abdomen radiograph shows numerous gallstones in the right upper quadrant (circle). This patient’s chief complaint was right-sided upper abdominal pain. Although further testing is indicated, this radiograph again demonstrates why plain film imaging can be quite useful in diagnosing some types of abdomen pain.
Gallstones are seen on this radiograph that was a post evac view following barium enema examination. The barium enema exam was a follow up to chronic upper and lower abdomen pain. These gallstones are seen in the RUQ (arrow).
The barium enema examination (BaE) is another study that is sometimes used to evaluate abdomen pain. It is not commonly performed for acute pain seen the emergency rooms even if the pain is thought to have origin in the gut. But it warrants mention here because the barium enema exam can provide useful evaluation of the large intestine and the appendix when it is visualized. The basis for a barium enema to evaluate RLQ pain associated with appendicitis is rooted in the controversy over whether or not chronic appendicitis is a real entity. Surgeons and physicians still debate the idea of the existence of chronic appendicitis. The strongest argumentatively evidence for chronic appendicitis pain is that some sufferers are successfully managed with appendectomy. Based on this some surgeons suggested that a nonvisualized or partially filled appendix, or one that drains slowly over a few days following a barium enema exam might suggest a chronic form of appendicitis. Controversially, a nonvisualized appendix finding is not accurate enough to perform an appendectomy in most cases. This is because nearly 15% of patients receiving a barium enema will have a nonvisualized appendix. Most of these will have a normal histological report. Based on these findings the nonvisualization theory is unreliable for proving chronic appendicitis. Irregular filling of the cecum can be an indicator of edema or inflammation, which is more reliable finding. However, when a barium enema exam is requested on an emergency basis a water-soluble contrast agent is recommended. The risk of perforation is considered high with acute appendicitis so barium is always contraindicated.
A positive contrast agent enema can differentiate many bowel disorders such as Crohn’s disease, right-sided diverticulitis, regional ileitis, and many others. It can be performed as a double contrast study using air contrast to evaluate for polyps, cancer, and other luminal bowel and mucosal pathologies. When diagnostic imaging is required on an emergency basis a CT scan and or an ultrasound examination is the preferred study method because it is quick and has high specificity for many pathologies. Barium enema examination remains in radiology’s repertoire of imaging exams because it can narrow differentials like diverticulosis and inflammatory bowel diseases.
This radiograph shows scattered diverticula throughout the abdomen. On the right is a magnified view of the left lower quadrant of the same radiograph. Notice the many scattered diverticula throughout the sigmoid and descending colon (arrows) This patient have chronic diverticulosis, which can become inflamed (diverticulitis), a condition that can mimic appendicitis. The barium enema study can be helpful in identifying chronic diverticulosis and acute diverticulitis.
This barium enema radiograph shows the large intestine of a patient who does not have diverticula. Diverticulosis and diverticulitis can also be evaluated with thin slice CT using a good oral prep and or rectal contrast. Certainly the barium enema can rule out diverticulosis and other bowel pathologies such as inflammatory bowel syndrome and colon cancer.
Diverticula are small sacculations of mucosa and submucosa through the muscularis of the colonic wall. They develop between the teniae coli and mesentery where nerve and blood vessel pierce, an origin that accounts for their propensity to bleed. Diverticula can be found anywhere in the colon, but they occur predominantly in the descending and sigmoid colon. They do not normally develop in the rectum. Diverticula also occur in the small intestine, but they are less common than those arising from the colon. A Meckel diverticulum is a congenital form of out pouching derived from an unobliterated yolk stalk. It occurs exclusively in the distal ileum. Diverticulosis is relatively common and can be seen in approximately 10% of those undergoing a barium enema. When these sacculations become inflamed or rupture the condition is called diverticulitis and can mimic appendicitis when associated pain is located in the RLQ. Diverticulitis occurs when the neck of a diverticulum becomes occluded, resulting in inflammation, erosion, and microperforation. These microperforations cause pericolonic inflammation that can be severe. Diverticulitis can be somewhat easily differentiated from appendicitis because about ninety-five percent of cases occur in the left side of the colon. Right-sided diverticulitis accounts for 5% of cases and occurs more frequently in Asians. It is this right-sided diverticulitis that can mimic appendicitis when it occurs. Diverticulitis of the transverse colon or small intestine is rare.
These two fluorospot images show numerous diverticula’s in the sigmoid colon (left image) and transverse colon (right image). Yellow arrows point to the diverticula’s in both images. Barium enema examination can determine the presence of diverticula’s (diverticulosis) and inflammation of diverticula (diverticulitis). When diverticulitis occurs in the RLQ of the abdomen it can produce symptoms that mimic appendicitis.
1.5 CT Evaluation for Acute Appendicitis
For many years acute appendicitis and those differential illness that closely mimic it have been difficult to diagnose, especially on an emergency basis. The evolution of helical multi-detector row CT has led to ultra thin slice tomographic imaging and the ability to differentiate a greater number of disorders with a single scan. CT imaging has now become the gold standard for evaluation of acute appendicitis and many other acute abdominal pathologies. CT is a high quality imaging technology that allows for greater diagnostic latitude and reduction in invasive exploratory surgeries. Today emergency room physicians order abdominal CT scans for renal stones, diverticulitis, acute appendicitis, and many other abnormalities that cause acute abdominal pain. CT is highly specific and sensitive for many acute pathologies of the abdomen and has reduced time between diagnosis and treatment of patients. In reference to acute appendicitis, the accuracy of CT is partially due to its ability to reveal a normal appendix. Being able to see the appendix is an important sensitivity criterion for imaging the abdomen for acute RLQ pain. This requires thin slice imaging through the pelvis. The recommended slice thickness is 2.5 mm X 2.5 mm. If thinner cuts are needed through the appendix they can be reconstructed from the original slices so long as they were acquired at thin section and interval. We all know there will be times when the appendix is not seen even with CT, this may occur when the slice thickness is 5 mm X 5 mm or greater. A scan using thick slices should be avoided when acute appendicitis is part of the differential diagnosis for acute RLQ pain.
Computerized tomography for appendicitis can be performed on an emergent basis with or without oral contrast agent. In most cases intravenous contrast agent is highly recommended because it can ferret out other abdominal pathology when appendicitis is not the correct clinical diagnosis. There are many studies that attempt to provide scientific rationale for using or not using oral contrast for emergency abdominal scanning. The clearest example for when oral contrast agent can be omitted is when the patient is obese or has above average body fat. Fat will most likely separate bowel very well and provide good visualization of the appendix. If the patient has good body fat content stranding within the mesentery can be seen without intravenous contrast as well. At times the radiologist may elect to omit oral contrast because the patient’s condition warrants immediate diagnosis. This is especially likely when rupture may have occurred and surgical intervention may be needed immediately. Intravenous contrast may still be administered when it is not contraindicated even if oral contrast is omitted; the radiologist decides this at the time of the scan.
Thin patients because of low body fat are almost always scanned with oral contrast. When acute appendicitis is suspected and the scan is performed using oral contrast agent, it is recommended that a water-soluble oral contrast agent like gastrographin or gastroview be administered. A good oral prep consists of 30 ml gastrographin, mixed in 700-800 ml of water (which can be flavored) or mixed in juice. Approximately 400 ml is given immediately and the remainder given in two equal doses at 30 and 60 minutes. Oral contrast media should be allowed to work its way through the bowel for at least 90-120 minutes. Focused CT involves rectal contrast and scanning of the lower abdomen and pelvis. Focused CT is a quick way to evaluate for appendicitis but is not gaining in popularity among radiologist, emergency physicians, or with CT technologists. Whether oral and intravenous contrast should be used or should not be used in evry case does not have a consensus in the literature. Instead the current focus has moved toward finding an optimal CT scanning technique for acute appendicitis regardless of preparation. For this reason our focus is also on optimal CT scanning technique. Of course this is dependent primarily on scanning equipment, expertise of the radiologist, and careful planning of the all parameters of the scan by the technologist. Consultation with the clinical physician is also very important so as not to delay surgical intervention in cases where rupture is highly suspected and oral prep should be skipped.
Three imaging schemes have been proposed for CT evaluation of appendicitis. These are the unenhanced CT of the abdomen and pelvis, addition of oral and/or intravenous contrast media, and focused appendiceal CT using rectally administered contrast agent. While all of these methods have advantages and disadvantages, the exact method depends on radiologist preference and how the patient presents clinically.
Unenhanced CT of the Abdomen
In addition to the high diagnostic accuracy of CT, unenhanced imaging is recommended when the time between diagnosis and surgical intervention need to be significantly reduced. Because it does not require oral or intravenous radiographic contrast agents the patient can be scanned immediately when requested. Use of unenhanced abdominal CT relies on the specific need to evaluate the appendix quickly. Unenhanced CT has a high specificity for appendicitis because a narrow group of differentials is possible when there is "disproportionate“fat stranding in the abdomen, especially the RLQ of a symptomatic patient. Disproportionate fat stranding is described as a greater degree of fat stranding than bowel wall thickening. When this is seen in the area of the cecum and appendix the differential diagnosis is narrowed to include appendicitis. This is a general but consistent sign pointing to appendicitis or other disease involving the bowel. When coupled to other findings like periappendiceal inflammatory changes, free fluid, abscess, abdominal free air, appendiceal wall thickening, and an appendiceal diameter greater than 6mm a diagnosis of appendicitis can be confirmed. All of these changes can be seen with thin-sliced unenhanced abdominal CT.
Both CT images above demonstrate an axial section through the abdomen. These are unenhanced images taken without oral or intravenous contrast agents. Image “A” demonstrates the appendix (arrow) in a thin patient. This radiograph shows the appendix only because a thin slice thickness of 2.5 mm X 2.5 mm was used. This will demonstrate the appendixinf a thin patient even without oral contrast agent. “Image B” is a slice through the abdomen of an obese patient. Notice the good separation of the bowel allowing the mesentery to be appreciated. Being able to see the mesentery well will allow for visualization of stranding and periappendicular abscess even without oral contrast. Unenhanced CT imaging for appendicitis is better in obese patients with good mesenteric fat than is routinely seen with thin lean body fat persons.
Thin patients may need oral and I.V. contrast agents to enhance the study because of low mesenteric fat content and poor separation of the bowel on unenhanced CT. In one study the use of unenhanced abdominal CT showed diagnostic performance very similar to that seen with oral contrast. The diagnostic sensitivity for appendicitis was 95% and a negative predictive value of 96% for unenhanced CT. The same study had a positive predictive value is 97% vs. 89% with oral contrast and the accuracy of the study was 96% vs. 92% with oral contrast. Several studies have shown that non-contrast CT techniques to diagnose appendicitis provides equivalent or better diagnostic performance compared to CT scan with oral contrast, but this is a limited study. If the diagnostic differentials include a much wider differential and is not specifically aimed at appendicitis, then the enhanced CT scan is preferred.
Pathology like a renal stone is easily identified on unenhanced CT. This saves precious diagnostic time and time between diagnosis and treatment. The top picture shows a renalith in the right kidney (white arrow) the bottom CT image shows a uretherlith in the left kidney (yellow arrow)
Enhanced CT of the Abdomen
An enhanced CT scan of the abdomen is one in which the patient is given oral contrast agent to coat the mucosa of the digestive tract and intravenous contrast to enhance the blood vessels, lymphatics, and solid organs of the abdomen. Intravenous contrast enhances the bowel wall and mesentery, and will enhance an abscess, which helps distinguish abnormal pathology from normal tissues. The decision to give oral contrast or not give it is determined by the radiologist and is based on patient history, consultation with the requesting physician, and the differentials to appendicitis being questioned. Patient preparation should include explaining to the patient what is involved in the CT study. If oral contrast is to be administered then explain the proper time schedule for ingesting it. Various oral preps can be used, for example, water may be used if a pancreatitis with stone is suspected, or barium sulfate solution, or a water-soluble media like gastrographin or gastroview if appendicitis with possible rupture is expected. When acute appendicitis is suspected and an emergency CT scan is performed using oral contrast agent, it is recommended that a water-soluble oral contrast agent like gastrographin or gastroview be routinely administered. Whenever there is potential that the bowel may be perforated premixed barium sulfate CT contrast should not be used, instead, a water-soluble oral contrast agent should be administered. The patient should be NPO (nothing by mouth) 2 hours prior to giving oral or I.V. radiographic contrast agents if possible. A good oral prep consists of a homogenous mixture of 30 ml gastrographin, mixed in 700 ml of water, which can be flavored, or mixed entirely with juice. Approximately 400 ml of the solution is given to the patient initially then at 30 minutes 200 ml given, and the remainder given at 60 minutes. When oral contrast is administered to see the appendix the time from ingestion to scan should be no less than 90 minutes. Sometimes due to nausea, or inability to drink large amounts of fluid it may be necessary to have the patient continuously sip the solution slowly for two hours. Oral contrast agents can be given through a nasal gastric tube (NGT), or gastric and jujeneal tubes. In some cases a selective CT scan of the lower pelvis can be performed using rectal contrast.
An intravenous radiopaque contrast agent is used in most cases when oral contrast is administered. The benefit of using intravenous contrast agent in diagnosing appendicitis is well documented. Because intravenous contrast opacificies blood vessels this allows the radiologist to see mesenteric blood vessels and lymphatics associated with the appendix. Intravenous contrast enhances the bowel wall so that an inflamed bowel like the cecum is seen. This is important since inflammatory bowel disorders are more easily diagnosed with intravenous enhancement than without it. In addition, solid organs such as the liver, spleen, kidneys, and pancreas are better evaluated with intravenous contrast. Blood vessels, lymph nodes, and mesentery enhance nicely with intravenous iodinated contrast, which is why many radiologist prefer it.
All patients without exception must be screened for compatibility with intravenous iodinated contrast agents before administering. The purpose of a good screening is to make sure each patient does not have known contraindications to radiographic contrast agent. Our goal is to reduce the likelihood of a reaction, or contrast induced health complication. A compatibility profile should include a complete review of medication and food allergies, particularly iodine allergy. The patient history should include a search of the medical record for information related to medication allergy, but be aware it may not be complete. Even newer electronic medical charts may not be completely updated with all the information you may need to know about your patient’s allergy risk. Always ask the patient if they are allergic to any medications, and what medications they are currently taking. The goal is to discover any incompatibilities to iodinated contrast media, or drugs used to treat radiocontrast allergies. Each patient should be asked if they have ever been given intravenous contrast agents, if so, specifically ask if there was any a complication or allergy. A complete history should be taken to include heart disease, lung disease (asthma, cancer, etc), liver disease, kidney disease, thyroid disease, sickle cell disease, adrenal gland tumors, multiple myeloma, diabetes, and pregnancy. Each of these risk factors should be further explored when the patient reports adverse findings. Patients who have no medical history for any of theses do not require further investigation prior to administering radiographic iodinated contrast agent. Screening alone does not guarantee that no complication may occur since many patients have never received iodinated contrast agents.
A detailed patient history is required for any patient with a history of iodine allergy, diabetes, renal dysfunction, or is over the age of 70. Any patient who has had a prior allergy-like reaction to contrast media, or allergic diathesis may be predisposed to possible reaction. These cases should be referred to the radiologist for consultation. Shellfish and dairy products do not have a reliable correlation to iodinated contrast media reaction; however the ACR recommends further clarification of patient histories to include type and severity of any reactions to foods or medicines to sort out those atopic individuals who may have increased risk. A complete patient screening should be presented to the radiologist at the time the protocol is requested for the CT scan. This screening should include recent blood urea nitrogen (BUN) and serum creatine laboratory test results that is no more than 30 days old any patient with an adverse history, previous high labs, renal dysfunction, diabetic, or over the age of 70. The serum creatinine level is a reliable screening for renal function and should be taken on all diabetic and elderly patients. Creatinine is a product of muscle and therefore elderly patients may have low creatinine levels due to lack of toned muscle mass and may have undetected underlying poor renal function. This is why patients over the age of 70 must be screened even if they are not using metformin. Further consultation with the ordering physician may be needed to make sure all aspects of the patient history are considered, for example, if renal function is slightly depressed pre and post hydration may be prescribed.
Dialysis patients typically will have very high serum creatine and may be given intravenous contrast so long as they will be dialyzed within 24 hours. These patients will need the approval of the radiologist before administering contrast agent. Borderline high creatine patients may be prescribed some form of medication like mucomyst to protect the kidneys. Other options may include pre and post contrast hydration using normal saline, and/or the use of visipaque. Visipaque is currently the only iso-osmolar iodinated contrast agent on the market. It has been shown in clinical trials and in current regular use to have low nephrotoxic effects.
Without exception all diabetic patients must be further screened for metformin (glucophage) use prior to administering intravenous iodinated contrast agents. Metformin is an oral antihyperglycemic agent often prescribed for non-insulin-dependent diabetes mellitus (Type II). It is also well known by its common name glucophage and may be found in several generic formulations and proprietary forms. Diabetes in many type II diabetics is controlled by diet; however, in some patients whose diabetes is not controlled by diet alone metformin is a commonly prescribed drug. Physicians like to prescribe it for tolerant patients because it has dual functions of decreasing liver production of glucose and increasing cellular uptake of glucose. By stimulating these two mechanisms the patient’s serum glucose level is suppressed. It is important that prior to administering intravenous radiopaque contrast agent that we screen every diabetic patient for metformin use because it can have adverse effects when the two are mixed. It has been shown that in a small percentage of patients using metformin lactic acidosis can develop following intravenous iodinated contrast administration. A most severe adverse side effect of metformin iodinated contrast reaction is lactic acidosis. Injury is initiated through mechanisms involving the intestine. Lactic acidosis is a fairly rare problem occurring in approximately 0.084 cases per 1000 patient years. This is a small global statistic for any individual that acquires contrast induced metformin lactic acidosis; however its significance lies in the high mortality rate, which is about 50%. Therefore, the technologist must carefully screen these patients to avoid this possible outcome.
In some patients with decreased renal function radiocontrast can induce nephropathy. The best indicator of those at risk is elevated serum creatinine greater than 1.2 mg/dl or creatinine clearance less than 80 mL/min. To help prevent adverse contrast induced nephrotoxicity (CIN) the technologist should consult the radiologist whenever the serum creatinine is found to be equal to or above 1.3 mg/dl. Certain conditions are predisposed to contrast induced nephrotoxicity. Among them are diabetes, preexisting renal renal insufficiency, dehydration, cardiovascular disease, advanced age, hyperuricemia, multiple myeloma, some drugs like chemotherapeutics and nonsteroidal anti-inflammatories. The basis for this precaution is that retrospective studies showed that CIN occurred in 22% of high risk patients who underwent coronary angiograph. High risk was defined as those patients with preexisting renal insufficiency or having preexisting renal insufficiency combined with diabetes mellitus.
Prior to administering iodinated contrast agent to a patient taking metformin their physician should be notified. Without exception all metformin use must be terminated following contrast media injection for at least 48 hours. They should see their physician after two days to have them authorize the restart of metformin. Metformin is released from the body through secretion mechanisms of the kidneys. Normal kidneys secrete about 90% of the drug in 24 hours. But if renal function is impaired (as indicated by a high serum creatine) the action of metformin on the intestine may be prolong raising the potential for lactic acidosis.
Now let’s get back to our discussion of the enhanced CT scan of the abdomen for appendicitis. One disadvantage of the enhanced CT scan is that the time between diagnosis and surgical intervention for severe acute appendicitis is increased enhanced abdominal CT. This is because the patient usually drinks for an hour and an half to two hours before the study is initiated. The diagnostic performance of enhanced abdominal CT is very similar to that seen without oral contrast for appendicitis. Current data shows enhanced abdominal CT to have a sensitivity of 95% and a negative predictive value is 96%. The positive predictive value is 89% with oral contrast and the accuracy of the study is 92%. Don’t let these numbers fool you, the enhanced CT may show similar or even slightly lower overall diagnostic statistics compared to unenhanced studies. But it should be applauded because it often shows pathologies not easily seen without contrast. For example, an enhanced CT can help characterize lymphadenopathies, occult vascular diseases, free air, abscess, fat stranding, appendiceal wall thickening, and many illnesses that include appendicitis in the differential.
Often radiologists prefer the enhanced CT scan for emergency patients with abdominal pain because it can image a wider range of pathologies. When the patient is thought to have appendicitis but is diagnostically proven to not, then the enhanced CT scan has even ore significance. So many radiologists prefer to get an enhanced CT scan on all emergency need patients who are not suspect for a ruptured appendix.
This enhanced CT was taken for a history of appendicitis. It revealed a thicken bowel wall (white arrow on left CT image) and an intusscesspted bowel (white arrow on right CT image). It is important for the radiologist to determine if the bowel is necrotic and therefore the enhanced CT is superior for these diagnostic issues compared to unenhanced CT.
These three CT axial slices demonstrate colitis in the ascending colon. This mimicked appendicitis in this patient. The enhanced CT with oral and intravenous contrast agents help to differentiate the bowel wall, which is notably thickened.
The CT Exam Protocol
The emergence of a standardized CT protocol for appendicitis imaging is possible because modern CT scanners are capable of thin slice imaging. The protocol used in this module is based on the slice thinness possible with the general electric Lightspeed brand 16 or 64-slice multi-detector-row CT (MDCT). If intravenous contrast agent is used the scan can be taken at approximately 70-80 seconds post injection. We are not going to cover special techniques like “smart prep” which measures the Hounsfield density of a structure as it fills with contrast. “Smart prep” allows the technologist to start the scan when the desired measured amount of perfusion of an organ is reached. This technique is commonly used for abdominal and vascular imaging but is not covered in this discussion. A 70-80 scan delay with contrast injection will give a good evaluation of the liver, kidney nephrogram, spleen, intestinal wall, lymph nodes, mesentery, blood vessels, and venous perfusion of most abdominal organs.
Following the scanogram scout image the scan is performed in helical fashion with data acquired at 2.5 X 2.5 mm slice/interval setting. The scan begins just a few slices above the diaphragm and goes through the pelvis ischial tuberosities. The male prostate gland should be entirely included in the exam. The three CT images below demonstrate the starting plane for the scan. Always start above the diaphragm as is demonstrated by scanogram and image (A). This is to evaluate any possible herniation of abdominal contents through the diaphragm into the thoracic cavity. Scan the entire abdomen and pelvis so that all abdominal organs can be evaluated. Have the patient hold their breath for the entire scan, which will be short if a multi-detector row CT scanner is used. An intravenous contrast bolus of 100-125 cc for adults and 1 cc per kg for children and infants is recommended. An injection rate of 2.5 ml per second for adults is recommended. Peak enhancements of abdominal organs occur in the venous blood phase, which is about 70 seconds post injection. Axial helical mages can be further reconstructed at 1.25mm X 1.25mm, or even 0.625mm X 0.625mm through the appendix if the appendix is not visualized. Coronal images can be reconstructed if requested; coronal and sagittal reconstructions are seldom needed because the radiologist can generate these planes from the diagnostic workstation if reading from a picture archiving system (PACS).
These set of CT images; A-C demonstrates scanograms of the slice levels of their corresponding CT axial slice. CT image “A” demonstrates the starting level of the axial scan above the diaphragm. It is important to always include the entire diaphragm muscle just as is the requirement for the upright plain film abdomen x-ray. Beginning above the diaphragm is necessary because the dome of the liver and diaphragm must be included in the scan field.
These three scanograms and their respective CT images demonstrates some slice levels for the abdomen CT scan. The top CT image demonstrates a cut through the liver and kidneys, the middle through the bowel and mid abdomen, and the lower image through the cecum and bowel. These representative slices demonstrate the scan profile used for imaging the abdomen. A ruptured appendix is seen (white circles on middle and lower CT images).
In the next few sample slices we can see why thin slices of about 2.5 X 2.5 mm thickness can show great detail in the area of the cecum and appendix. In these slices the appendix is well demonstrated. One of the most important values of CT imaging is that the appendix can be demonstrated in most cases. This contributes to its high specificity and sensitivity for diagnosing appendicitis.
These 12 CT images are taken at 2.5 mm X 2.5 mm using a 16 MDCT GE Lightspeed scanner. This is a study in which oral water-soluble contrast agent was administered. There is an inflammatory process in the right lower quadrant of the abdomen consistent with appendicitis. A large appendicolith is present. The appendix itself is somewhat ill defined but obviously pus filled and dilated to 12 mm (white arrows). No obvious periappendiceal abscess present, however, there is fluid present and perforation is highly suspected. When appendicitis is present the appendix is seen in multiple slices when thin slice CT scanning is used apposed to thick image/interval slices.
CT images 10 and 11 are magnified so you can see the appendicoliths within the appendix. These are successive images taken at 2.5 mm by 2.5 mm interval.
CT indications for Diagnosing Appendicitis
Improvements in computerized tomography technology have allowed radiologists to clearly identify fat stranding within the mesentery. Research has shown that when stranding is found adjacent to a thickened bowel wall an inflammatory process outside the bowel is likely. Demonstrating stranding within the mesentery of a patient with acute abdominal pain suggests an acute process of the gastrointestinal tract, but the differential diagnosis is still wide. Disproportionate fat stranding is a center point for diagnosing acute gastrointestinal inflammatory process. The list of differentials that have disease processes outside the bowel wall when stranding is present on CT is short. The acceptable working definition of "disproportionate" fat stranding can be interpreted to mean stranding more severe than expected for the degree of bowel wall thickening. This finding on CT suggests a narrower differential diagnosis that is centered in the mesentery. Most likely the cause is diverticulitis, epiploic appendagitis, omental infarction, or appendicitis. Characteristically diverticulitis manifests with mild smooth bowel wall thickening and no lymphadenopathy. Epiploic appendagitis manifests with central areas of high attenuation and a hyperattenuated rim. Epiploic appendages are generally seen adjacent to the colon. Omental infarction is distinguished by its presence in the omentum. A dilated fluid-filled appendix characterizes appendicitis. Appendicitis may present with periappendiceal inflammation, abscess, phlegmon, free fluid, free gas bubbles, or even adenopathy along with disproportionate fat stranding.
On this axial CT image there is stranding in the mesentery and a large appendicolith within a swollen ruptured appendix (yellow arrow). Disproportionate fat stranding is a diagnostic feature of acute appendicitis on CT. The ruptured appendix has formed an abscess within the right lower quadrant of the pelvis.
The significance of disproportionate fat stranding is pronounced in these two axial CT images. Notice on these two CT image a significant amount of fat stranding is seen in the mesentery (blue arrows). Compare this to the non-stranding areas of the mesentery on the left side of the abdomen (orange arrow) in each CT image. Notice the thickened wall of the appendix (yellow arrow) that is also a key to the diagnosis of appendicitis and potential for rupture.
One of the most outstanding indicator of appendicitis is a swollen appendix that is filled with fluid. We can see swelling, dilation, and a fluid filled appendix on the CT image below. Adjacent cecal wall is greatly enhanced due to fluid within the appendix and surrounding mesentery. Notice that there is an appendicolith blocking the passage to the appendix. These changes are caused by cyclic changes characteristic of appendicitis. The mild posterolateral wall thickening of the cecum (cecal bar sign) is caused by a partially coapted cecal wall adjacent to the occluded appendceal orifice. Fortunately this person does not have a periappendiceal abscess so an early appendectomy was successfully performed.
Notice the enhanced wall of the appendix and cecum, a large appendicolith, and a swollen fluid filled appendix in the CT image above. The appendix is swollen to a measurement greater than 10 mm (yellow arrow). Stranding within adjacent mesentery is also noted. Fortunately the appendix has not ruptured at the time of imaging. No oral prep was administered, which decreased diagnostic imaging time.
This CT image demonstrates an inflamed ruptured area of the appendix and abscess. This axial contrast-enhanced CT image shows focal disruption of the wall of the appendix. An abscess surrounds the appendix. An appendicolith is seen and gas is forming within the abscess. Fat stranding is also noted in the mesentery surrounding the appendix. This careful detailed visualization of the appendix showing appendicitis shows why CT is a highly rated study for RLQ abdominal pain.
1.6 Ultrasound of the Appendix
Ultrasound imaging is another method of evaluating the right lower abdomen for appendicitis. It is especially useful for the very young, thin patients, and sometime effective when pregnancy is a factor. A clear advantage for using ultrasound is that it does not use ionizing radiation. Although CT is the gold standard for imaging and diagnosing appendicitis there are good reasons to choose to perform ultrasonography: 1) it is relatively low in cost, 2) is considered safe even during pregnancy, 3) and is available in most institutions. When used selectively the diagnostic accuracy is reported to range from 71 to 97 percent. Reasons for considering ultrasonography include:
It was once thought that a normal appendix could not be detected by ultrasound so any visualized appendix was considered abnormal. But this has been completely disproved as visualizing the appendix on ultrasound produced many false positives. This led to the development of specific ultrasound criteria for acute appendicitis commensurate with improvements in ultrasound technology. Visualizing the appendix still remains the most difficult part of the ultrasound exam. Currently the diagnostic criteria for appendicitis includes complete visualization of the appendix, measuring its outer diameter, compressibility, and echogenic inflammatory periappendiceal fat changes, have been established. Development of high-resolution ultrasound equipment has increased visualization of noninflamed appendices to 60%. This has eliminated the visualization of the appendix criterion as the single basis for diagnosing appendicitis, which has greatly reduced the number of ultrasound driven false positives.
Data for all age groups suggests that when the outer diameter of the appendix measures greater than 6 mm the sensitivity is 100%, but the specificity (about 64%) for appendicitis is low. So this criterion alone is not enough for the diagnosis of appendicitis. Compression of the appendix as a single criterion is specificity poor. Echogenic inflammatory periappendiceal fat change has proven to be a reliable factor (sensitivity 95%), but has a poor specificity (50%). Color Doppler is a weak diagnostic tool especially when the appendix is deep within the abdomen or is gangrenous. Compiled data suggests that a series of diagnostic criteria is the best approach to definitive ultrasound diagnosis. When the appendix is completely visualized, compressed, measured, and the surrounding tissue scanned to demonstrate inflamed periappendiceal fat), ultrasound diagnosis is very accurate.
Sonographers are challenged by these criteria as finding an appendix remains a most difficult criterion in most adults. Often it is reported that the appendix is elusive and not found. It is particularly difficult to demonstrate a normal appendix (to exclude appendicitis) when the patient is obese. Obesity can be a factor that prevents a satisfactory examination because compression of the appendix is often inadequate. A CT scan can identify appendicitis in obese persons better than ultrasound exam. Other difficulties like an associated ileus in which a gas-filled bowel may overly the appendix producing shadowing. Sometimes the external iliac artery and vein can provide a good landmark for finding the appendix because of its location and it being pulsatile, compressible, and having Doppler flow. The accuracy of ultrasound exam can be diminished by normal anatomical conditions like being retrocecal (60% of population), hidden from the transducer. About 28% of pediatric patients present with a retrocecal appendix that is not hidden. Other times underlying pathology can lead to a false-positive results like Meckel’s or cecal diverticulitis, inflammatory bowel disease, pelvic inflammatory disease, and endometriosis. So the sonographer must be especially careful when pathology presents so that the correct diagnosis is made based on the consolidated criteria.
The suggested method for ultrasound scanning is graded compression. This technique is universal for imaging any part of the bowel. Compression displaces gas within the bowel and brings the bowel closer to the transducer. The suggested scan technique begins by placing the transducer in a transverse position and applying deep compression. Beginning at the hepatic flexure the bowel is traced down to the cecum. This may be quite painful for a patient who is suffering acute abdominal pain caused by appendicitis. The patient should point the location of pain, which may be directly over McBurney’s point or elsewhere the appendix is located. To help manage the patient’s pain the sonographer should slowly releasing compression so that rebounding is avoided. The highest scan frequency is selected and the patient scanned from the umbilicus through the point of pain. Some protocols call for scanning the entire pelvis of all females with right lower quadrant pain having a normal appendix. Other protocols require scanning the renal and biliary systems of all patients with a normal appendix and RLQ abdomen pain.
There are the three main presentations of acute appendicitis on ultrasound examination: 1) cross-section appearance measuring greater than 6 mm diameter and often 7-12 mm. The wall thickness can measure almost 3 mm or greater, 2) progressed appendicitis can demonstrate a gangrenous appendix. The lumen distends tremendously sometime upwards to 2 cm and is not compressible. An appendicolith may be present which will cast an acoustic shadow, 3) or a perforated appendix is demonstrated when the appendicular wall has ruptured producing fluid or a newly formed abscess. The appearance is hyperechoic with an echo-poor abscess surrounding the appendix. There may be a reflective omentum around the appendix, a thickened bowel, and enlarged lymph nodes. Asymetrical wall thicken may indicate perforation. In order to demonstrate all the possible presentations of appendicitis it is important that the entire appendix is visualized. This can be difficult to achieve although it is generally less difficult when the appendix is swollen and inflamed. Often early stages of appendicitis are focal or localized to the tip or other region before full cyclic changes have progressed throughout the appendix. For this reason the entire appendix is imaged from the stump through the tip. Consider the ultrasound images below of the appendix, which demonstrates appendicitis.
This is a longitudinal ultrasound image of the appendix. It demonstrates an abscessed appendix having the diagnosis of acute appendicitis. This image demonstrates a diseased appendix and the infection is seen tracking through the surrounding tissues.
This ultrasound image demonstrates the appendix in cross-section; this is the typical “target-like” appearance. A normal appendix is considered to have a diameter of less than 6mm, whereas a fluid filled appendix adds to the diagnosis of appendicitis. A fluid filled appendix will be non-compressible and may have a wall thickness upward to 2 cm has been demonstrated in appendicitis. Notice the fluid within the appendix (center of image) and thick appendicular wall.
1.6 Treatment of Appendicitis
The most common treatments for acute appendicitis include surgical resection of the appendix, antibiotics, and placing a drainage catheter when there is an abscess caused by rupture. Several methods of performing an appendectomy include open incision method and laparoscopic approach. Which method is used is the surgeon’s decision based on the patient and presentation of appendicitis. Generally open operation is chosen when the appendix has or may rupture, and laparoscopic approach is favored for early appendicitis or when it is questionably normal. Other considerations include the cost of appendectomy since it is the most frequently performed surgical emergency. The costs associated with laparoscopy are greater than with an open operation, but the hospital stay is shorter such that the overall costs are about the same. Laparoscopic visualization of other abdominal structures is another added advantage, especially if the appendix appears normal. The recovery time is shorter for the patient undergoing a laparoscopic operation than open operation. Open operation requires the appendix and its blood supply be tied off with sutures and then removed through the open incision. A laparoscopic operation can be performed in the same time that it takes to perform an open appendectomy through carefully placed ports giving entry into the abdomen.
These two pictures demonstrate the laparoscopic removal of the appendix. The blood vessels within the mesoappendix are first stapled, and then the appendix is stapled, cut and removed through the access port.
Sometimes there are associated complications of appendicitis due to rupture before surgical intervention. The most common complication of appendectomy is infection of the wound from an open surgical incision. Infection of the appendectomy incision is a rather rare complication (about 3% of cases). When infection occurs it may vary in severity from mild to moderate to severe. Mild and moderate infections may only have redness and tenderness over the incision site. This type of infection is usually treatable with antibiotics. Severe deep seeded infections require antibiotic and some form of invasive treatment like surgery or placement of a drainage catheter. Surgeons attempt to remove all infection associated with a ruptured appendix during appendectomy. Surgeons attempt to remove all infection associated with a ruptured appendix during appendectomy. However, some infections do persist as bacteria multiply because of extensive pre-operative seeding. The surgeon may elect to not close the incision for a few days to allow the womb to drain and give time for antibiotic treatment to take hold. Another post surgical option if the infection produces an abscess is to have the radiologist place a drainage tube into it using ultrasound or more often CT guidance. The process involves placing a drainage catheter into the abscess and connecting the external end to a slow vacuum drainage reservoir.
The number of cases where death has occurred because of a ruptured appendix has dramatically decreased. Nowadays it is almost never the cause of death because surgical intervention, excellent antibiotics and good diagnostic information from ultrasound and CT. Deaths due to appendicitis are rare with the current incidence being less than 1%. Because of good diagnostic imaging information and treatments for abscess recovery is almost always complete even with severe complications. Abscesses are also fairly uncommon (occurrence is <5%) and can usually be managed by placing a catheter to drain the pus using CT. The CT guided drainage catheter placement is an invasive procedure that is performed to drain pus from an abscess. The CT image below demonstrates how a grid is placed on the abdomen to localize the place of entry to access the abscess for draining.
This CT image demonstrates the placement of a localizing grid (white arrow) to mark the slice level for needle entry to place the drainage catheter. The yellow arrow indicates the abscess formed by a rupture of the appendix. This image demonstrates why CT guided drainage of an abscess is a preferred method of treating an abscess. A large abscess is easily seen on this unenhance localization image.
Following conscious sedation and preparation of the site the next step is percutaneous needle entry into the abscess. This CT image shows the entry needle advanced to the abscess. Slight motion is seen due to the patient breathing. Once the radiologist establishes entry into the abscess aerobic and anaerobic cultures are taken then the abscess is drained. Next the catheter is slid into place over a guide wire.
This CT image demonstrates the successful placement of a drainage catheter into the abscess. The external part of the catheter (white arrow) is connected to a reservoir. The drain will stay in place until the physician determines the abscess is sufficiently reduced and antibiotic treatment is effective.
Patient history and physical exam are the most reliable clinical indicators of acute appendicitis; however, only 50 to 55% of patients present with reliable classical symptoms. For those atypical presentations, diagnostic imaging is the most reliable alternative. Plain film radiography can in limited cases show bowel obstruction, free-air associated with a perforation, and occasionally a rare appendicolith is visualized. CT is the preferred standard imaging method because it is the most reliable method of visualizing the appendix. Thin slice CT images have demonstrated great detail about the abdomen whether enhanced or unenhanced scan protocols are used. With nearly 250,00 new cases of appendicitis seen annually in the United States, nearly 35% of which present with rupture or abscess, CT has greatly reduced the diagnostic differentials in dealing with atypical cases. When other illnesses like renal stones, inflammatory bowel syndromes, intussusception, Meckel’s diverticulum, diverticulitis, and many others mimic appendicitis, CT is able to sort these differentials using an appendicitis imaging protocol. CT enjoys a sensitivity and specificity of greater than 95% for detecting appendicitis. Graded compression ultrasound is also very effective in diagnosing appendicitis. This is especially useful in children when the appendix lies retrocecal and is unobstructed by bowel. Ultrasound exam is especially difficult because the appendix must be visualized in its entirety to avoid missing focal appendicitis. Being able to measure the cross-sectional diameter of the appendix and wall thickness is also part of the diagnostic criteria making it difficult to confirm in early appendicitis. Yet ultrasound has a high specificity and sensitivity in thin, young patients. Altogether, radiology has help raise the level of true positive and true negative diagnoses of appendicitis and decreased false positive and false negative diagnoses. Radiology protocols and equipment will continue to improve over the next decade.
Points to Ponder!
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