阑尾炎的不典型CT表现

Appendicitis:Atypical and Challenging CT Appearances,Introduction,Appendicitis is commonly seen in medical practice, and its preoperative diagnosis is increasingly reliant on imaging, particularly computed tomography (CT), with clinical manifestations and laboratory test results playing a less important role.The imaging-based diagnosis of appendicitis is not always straightforward. To achieve an accurate diagnosis, radiologists must be familiar with atypical as well as characteristic CT appearances of appendicitis.This online presentation reviews:The pathophysiology and etiology of appendicitis, including various causes of secondary/reactive appendicitis and mimicsAtypical and complicated cases of appendicitisAdvantages and potential pitfalls of using appendiceal caliber and/or appendiceal filling by oral contrast material as diagnostic criteria at CTThe importance of comparing current imaging studies with previous studies when evaluating early, chronic, and resolving appendicitis,Teaching Points,An increase in appendiceal caliber between serial CT examinations, even in the absence of adjacent fat stranding, may signal early-stage appendicitis.However, increased appendiceal caliber alone is not a reliable indicator of appendicitis and must be considered alongside the patients clinical history and other imaging findings to avoid misdiagnosis.The presence of oral contrast material within the appendix conflicts with a diagnosis of acute appendicitis and can be used as supporting evidence for a nonobstructed appendix in equivocal cases, such as when appendiceal mural thickening is seen without substantial periappendiceal fat stranding.Primary appendicitis should be distinguished from secondary or reactive appendicitis, which can be caused by cecal and/or terminal ileal diverticulitis, terminal ileitis, active Crohn disease, colitis, or an acute gynecologic disease process.Clinical mimics of appendicitis include appendiceal mucoceles and neoplasms.,Learning Objectives,After viewing this presentation, participants should be able to:Discuss the advantages and potential pitfalls of using appen-diceal caliber and/or appendiceal filling by oral contrast material at CT to determine whether acute appendicitis is present. Recognize the broad spectrum of CT appearances of atypical, complicated, and secondary or reactive appendicitis.List potential mimics of acute appendicitis.,CT Protocol,Controversy surrounds the optimal CT protocol for evaluating patients with signs and symptoms of acute appendicitis, and the value of intravenous, oral, and rectal contrast agents is debated.At our institution, we routinely administer both oral and intravenous contrast material and acquire 5-mm-thick axial sections with 3-mm coronal and sagittal reconstructions. The targeted interval between the administration of oral contrast material and scanning is 60 minutes.Alternatives include the use of intravenous contrast material alone, oral contrast material alone, rectal contrast material alone, or no contrast material at all.In many centers, patients with right lower quadrant pain who are evaluated in the emergency department undergo CT without contrast material. The chosen protocol should satisfy the needs of referring clinicians and be appropriate for the particular patient, although that ideal may be difficult to achieve in emergent settings.Dose reduction strategies should be used to minimize the patients exposure to radiation while maintaining the image quality needed to achieve a high level of diagnostic accuracy.,Advantages and Disadvantages of Using Oral Contrast Material,Advantages,Allows improved diagnostic accuracy in patients with a paucity of intra-abdominal fat and resultant susceptibility to volume averaging of bowel, vessels, and other visceraAllows a decreased number of false-negative findings in certain settingsIn equivocal cases, appendiceal filling can provide supportive evidence for a nonobstructed appendix,Disadvantages,Increases scanning time, which may delay patient careMay mask appendicolithsLeads to decreased patient satisfaction with the imaging examination (due to unpleasant taste and potential side effects such as nausea, vomiting, and diarrhea) Increases the cost of the imaging examination,Pathophysiology of Acute Appendicitis,Appendiceal inflammation leads to appendiceal wall thickening and distention.Possible complications of acute appendicitis include Abscess GangrenePerforationPeritonitisIn the case shown here, the underlying cause of appendicitis was uncertain, but obstruction of the appendiceal lumen by the appendicolith or by lymphoid hyperplasia was suspected to play a role.,Figure 1. Coronal CT image shows a dilated fluid-filled appendix with a calcified appendicolith (arrow) and extensive extraluminal fluid and fat stranding (arrowheads) in the right lower quadrant, findings suggestive of perforated appendicitis.,Atypical Location: Normal Variation versus Herniation,Normal variationNormal appendix is relatively mobile and may be found in a retrocecal, subcecal, retroileal, preileal, or pelvic siteAmyand herniaHerniation of the appendix into an inguinal herniaOccurs in 6 mmAbnormal appendiceal wall enhancementPeriappendiceal strandingAppendicolith may be present“Arrowhead” signFocal symmetric thickening of the upper cecal wall where it approaches the obstructed appendiceal orifice, with an arrowhead-shaped collection of oral and/or rectal contrast materialObservation of this sign allows diagnostic sensitivity of 30% and specificity of 100%, according to Rao et al,Figure 23. Arrowhead sign in early-stage appen-dicitis. Coronal CT image shows focal symmetric thickening of the wall of the upper cecum where it approaches the orifice of the obstructed appendix. Note the arrowhead-shaped collection of oral contrast material (arrow) within the appendix.,Atypical Appendicitis with Normal White Blood Cell Count,Important: Although leuko-cytosis is often associated with acute appendicitis, a normal white blood cell (WBC) count alone does not allow the ex-clusion of appendicitis. When the WBC count is normal or borderline high, concomitant elevation of the absolute neutrophil count (ANC) or percentage of neutrophils supports a diagnosis of acute appendicitis.,Figure 24. Atypical acute appendicitis without leuko-cytosis. (a) Coronal CT image shows a dilated 1.4-cm appendix (arrow) with only minimal periappendiceal fat stranding in a 59-year-old immunocompetent man with 2 days of right lower quadrant abdominal pain and normal WBC count, ANC, and percentage of neutrophils. (b) Axial CT image shows a mildly dilated 1-cm appendix (arrow) without substantial periappendiceal fat stranding in a 22-year-old immunocompetent man with a normal WBC count and normal percentage of neutrophils but marginally elevated ANC. Pathology reports indicated acute appendicitis in both patients.,a.,b.,Atypical Appearances: Tip Appendicitis,Figure 25. Tip appendicitis. Evaluation of the appendix on coronal CT images reveals a normal-appearing proximal portion filled with oral contrast material (arrow in a), a nondilated middle portion (arrow in b), and a markedly thickened distal portion (arrow in c) with associated periappendiceal stranding, findings suggestive of tip appendicitis. The diagnosis was confirmed at pathologic analysis.,a.,b.,c.,Important: Close inspection of the entirety of the appendix, from its origin to its most distal portion, is essential at imaging in order to avoid missing the diagnosis of tip appendicitis. Note that the normal appendiceal tip is bulbous in configura-tion and is expected to be wider in diameter than the rest of the appendix.,Atypical Appearances: Stump Appendicitis,Inflammation of residual appendix after appendectomy is known as stump appendi-citis. Surgical resection of the inflamed appendiceal stump with or without invagin-ation, referred to as repeat or completion appendectomy, is usually recommended.A recent literature review performed by Kanona et al showed that 37% of cases of stump appendicitis occurred after initial laparoscopic appendectomy and 63% occurred after initial open appendectomy, contrary to earlier reports that suggested an increased incidence rate after appen-dectomy with a laparoscopic approach. The interval between initial appendectomy and repeat appendectomy varied from 9 weeks to 50 years.Rarely, an inflamed epiploic appendage may calcify and mimic stump appendicitis.,Figure 26. Stump appendicitis. Axial CT image obtained approximately 2 years after laparoscopic appendectomy shows a long appendiceal remnant (arrow) with adjacent fat stranding, findings suggestive of stump appendicitis.,Atypical Appearances: Focal Inflammation of Appendix,Figure 27. Appendix with rarely seen focal inflammation. Axial (a) and coronal (b) CT images show a 1.5-cm appendix (arrow) containing fluid and gas from the middle to the distal portion. These findings are suggestive of an intraluminal abscess in the setting of acute appendicitis. Pathologic analysis showed focal inflammation with a bulging appendiceal luminal wall containing fecal matter.,Important: The presence of gas in the appendiceal lumen does not permit the exclusion of appendicitis, and when seen with other features of acute appendicitis, it is suggestive of complicated appendicitis.,a.,b.,Complicated Appendicitis: Perforation,Classic CT findings of perforated appendicitis areAbscessExtraluminal airExtraluminal appendicolithVisualization of one or more appendicoliths increases the probability of appendiceal perforationAppendicoliths may accelerate the rate at which perforation occurs,Figure 28. Perforated appendicitis. Axial CT image shows an appendicolith (arrow) with an atypical, extraluminal location in the anterior pelvis, a finding indicative of appendiceal perforation.,Complicated Appendicitis: Perforation (continued),Horrow et al identified five CT findings that collectively yielded 95% sensitivity and specificity for a diagnosis of perforated appendicitis:Extraluminal airExtraluminal appendicolithAbscessPhlegmonDefect in mural enhancement (individual feature with the highest sensitivity, at 64%),Figure 29. Perforated appendicitis. Coronal CT image shows disruption of the appen-diceal wall by extraluminal air (arrow), a finding indicative of perforation.,Complicated Appendicitis: Perforation (continued),Figure 30. Perforated appendicitis with free intraperitoneal and right retroperitoneal air in an 82-year-old woman. Axial (a) and coronal (b) CT images show air collections anterior to the liver, tracking into the retroperitoneal space, along the right paracolic gutter, and into the region of the cecum. Such extensive pneumoperitoneum is infrequently seen in cases of appendicitis.,a.,b.,Complicated Appendicitis: Abscess,Abscess is the most frequent complication of perforated appendicitis.A localized abscess occurs if periappendiceal fibrinous adhesions develop before the appendix ruptures.Infection may spread to adjacent structures and spaces, such as the iliopsoas muscles and retroperitoneal tissues, if the abscess is not promptly diagnosed.,Figure 31. Perforated appendicitis with a complex multicompartmental abscess extending into the retroperitoneal tissues, right psoas muscle, right iliacus muscle (arrow in a), and posterior subcutaneous tissues of the right flank (arrow in b). Culture of fluid from the abscess showed Klebsiella infection.,a.,b.,Complicated Appendicitis: Peritonitis,When appendiceal rupture occurs before inflammatory adhesions form in early acute appendicitis, peritonitis may result.Peritonitis secondary to perforated appendicitis is more common in children than in adults because progression from inflammation to perforation is more rapid in children.Contrast-enhanced CT is helpful for distinguishing peritonitis from ascites.,Figure 32. Perforated appendicitis with resultant peritonitis in a 59-year-old woman. Coronal CT image obtained after appendectomy shows enhancing, thickened peritoneum (white arrow) and mild to moderate ascites (black arrow) in the patients abdomen and pelvis.,Complicated Appendicitis: Other Associated Findings,Pylephlebitis and pylethrombosisCaused by ascending infection along the draining mesenteric-portal venous systemGenitourinary involvementMay result in reactive hydroureter or hydronephrosisGangrenous appendicitisPneumatosis, shaggy appendiceal wall, and patchy areas of mural nonperfusion,Figure 33. Pylephlebitis secondary to appendicitis. Axial CT image obtained in a patient with appendicitis shows a focal linear region of hypoattenuation in the right hepatic lobe (arrow), a finding that likely represents thrombosis of the distal end of an anterior branch of the right portal vein.,Complicated Appendicitis: Bowel Obstruction,Bowel obstruction may occur due toNarrowing of the distal ileum because of periappendiceal inflammationAdhesions from appendectomy,Figure 34. Axial CT images obtained in the lower abdomen show multiple dilated small bowel loops containing differential air-fluid levels, findings consistent with a small bowel obstruction (arrows in a) secondary to appendicitis (arrow in b).,a.,b.,Complicated Appendicitis: Fistula,A fistula may form from a perforated appendix to adjacent bowel, bladder, vagina, uterus, or skin.Fistulation is a rare com-plication of perforated appendicitis.,Figure 35. Coronal CT image shows improving appendicitis with a probable fistula (arrow) to the adjacent sigmoid colon.,Chronic and Recurrent Appendicitis,Chronic appendicitisSymptoms last for weeks, months, or yearsRecurrent appendicitisCharacterized by repeated episodes of painIntervals between episodes may vary from weeks to yearsClinical manifestations may be the same as those of acute or chronic appendicitis,Figure 36. Chronic appendicitis. Axial CT images obtained 5 months apart in the same patient show a persistently dilated, fluid-filled appendix (arrow) without substantial adja-cent fat stranding. Even when conservative management of appendicitis fails, the result is not invariably a ruptured appendix.,a.,b.,Resolv