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Departments of 1 Radiology and 2 General Surgery, Istanbul International Hospital, Istanbul cad. No: 82 34800 Yesilkoy, Istanbul, Turkey
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Abstract |
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Introduction |
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The purpose of this study was to determine the diagnostic accuracy of thin section unenhanced helical CT protocol in adult patients with suspected acute appendicitis.
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Materials and methods |
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All CT scans were obtained using a helical CT scanner (Siemens Somatom Plus 4; Siemens, Erlangen, Germany). A single breath-hold helical scan was performed from the top of the L3 vertebral body to the pubic symphysis using 5 mm beam collimation and 8 mm s-1 table speed (1.6 pitch, 120 kV, 240 mA). No oral, rectal or intravenous (iv) contrast was administered. On average, the entire examination took less than 5 min to complete.
The hospital has Picture Archiving and Communicating System (PACS) network, and soft-copy reporting with Magic View 1002 monitors (Siemens, Erlangen, Germany) was used. CT scans were usually viewed on cine mode. Unenhanced CT findings of acute appendicitis included a thickened appendix with a diameter exceeding 6 mm with associated inflammatory changes in the peri-appendiceal fat and/or abnormal thickening of the right lateroconal fascia with or without a calcified appendicolith. A CT scan was interpreted as negative for appendicitis if the appendix transverse diameter was 6 mm or smaller, or if the appendix was not reliably identified.
Pathological findings from specimens of resected appendix served as the gold standard for the diagnosis of appendicitis. If surgery was not performed, clinical follow-up was obtained. If no surgery was undertaken and the patient's symptoms resolved, this was recorded as a true negative finding on unenhanced CT.
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Results |
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and 2).
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188 patients did not have acute appendicitis. In this patient group three normal appendices were surgically removed (false positives). Of these, two patients had caecal diverticulitis (Figure 3). 173 patients were followed clinically for up to 3 months after resolution of symptoms, and none had appendectomies.
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Statistical analysis of the final diagnosis based on unenhanced CT findings indicated a sensitivity of 96%, specificity of 98% and an accuracy of 97% for unenhanced CT in the diagnosis of acute appendicitis. The positive predictive value was 97% and the negative predictive value was 98% (Table 1).
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Discussion |
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To maximize diagnostic accuracy, a variety of CT protocols for the diagnosis of acute appendicitis have been described [4, 7, 8, 11, 12]. Visualization of the appendix is an important initial diagnostic goal.
Visualization of the appendix is strongly dependent on the type and quality of CT examination, although appendiceal size, amount of peri-appendiceal fat and degree of ileocaecal bowel opacification are important influencing factors [2, 3]. In complicated cases, dynamic cine review of images on the CT console may facilitate recognition of the appendix, terminal ileum and caecum. The normal appendix is identified in 67–100% of symptomatic adults who undergo thin section helical CT of the RLQ [8, 10–13, 14].
Appendiceal visualization is technique dependent, with the highest detection rates reported in patients who have received rectal contrast material [11–13, 15]. The normal appendix appears as a tubular or ring-like pericaecal structure that is either totally collapsed or partially filled with fluid, contrast material or air. The normal appendiceal wall measures less than 1–2 mm in thickness. The peri-appendiceal fat should appear homogeneous, although a thin mesoappendix may be present.
Definitive CT diagnosis of acute appendicitis can be made if an abnormal appendix is identified or if a calcified appendicolith is seen in association with pericaecal inflammation [2–5]. Appearance of the abnormal appendix varies with the stage and severity of the disease process. CT findings are most subtle in patients with mild, non-perforating appendicitis who undergo scanning shortly after the onset of symptoms. In these patients the appendix may appear as a minimally distended, fluid-filled, tubular structure 5–6 mm in diameter surrounded by the homogeneous fat attenuation of the normal mesentery.
The inflamed appendix usually measures 7–15 mm in diameter. Circumferential and symmetric wall thickening is nearly always present and is best demonstrated on images obtained with iv contrast enhancement [2, 3]. The thickened wall is usually homogeneously enhanced. Peri-appendiceal inflammation is present in 98% of patients with acute appendicitis [12, 13]. Although linear fat stranding, local fascial thickening and subtle clouding of the mesentery are characteristic findings in non-perforated appendicitis, they may be seen with microperforation. These findings of appendicitis may help to establish diagnosis in equivocal cases.
Perforated appendicitis is usually accompanied by pericaecal phlegmon or abscess formation. Associated findings include extraluminal air, marked ileocaecal thickening, localized lymphadenopathy, peritonitis and small bowel obstruction. Although a pericaecal phlegmon or abscess is strongly suggestive of appendicitis, these are non-specific findings that may be seen with other disease entities [2, 3]. The CT findings of recurrent and chronic appendicitis are identical to those of acute appendicitis [16].
Grosskreutz et al [17] revealed that the normal appendix was definitely identified in 51% of 203 patients studied using conventional CT techniques. Helical CT eliminates the potential risk of respiratory misregistration because images are obtained in a single breath-hold. Also, relatively thin section images can be obtained, images can be reconstructed at smaller intervals and multiplanar reformations can be performed [8]. In a recent study, Weltman et al [13] showed that the use of 5 mm section helical CT, compared with 10 mm section helical CT in the same patient, enabled the improved visualization of abnormal appendices (94% vs 69%), calcified appendicoliths (38% vs 19%) and peri-appendiceal inflammation (98% vs 75%).
Nowadays, enhanced or unenhanced helical CT has been widely used in the diagnosis of acute appendicitis. The potential advantages of performing unenhanced CT compared with enhanced CT include the ability to immediately scan a patient without any preparation, such as oral or rectal contrast material, and financial savings when iv contrast material is not used.
Helical CT has reported sensitivities between 90% and 100%, specificities between 91% and 99%, accuracies between 94% and 98%, positive predictive values between 92% and 98% and negative predictive values between 95% and 100% for the diagnosis of acute appendicitis [8–13].
Appendiceal CT protocols differ considerably with regard to the anatomical area to be included in the scan and the use of iv, oral and rectal contrast material. The most popular and conservative approach is to perform helical CT scanning of the entire abdomen and pelvis with iv and oral contrast material. Proponents of this technique believe that contrast enhanced CT is essential in the diagnosis of numerous inflammatory, ischaemic and neoplastic processes that may cause acute abdominal pain and may stimulate appendicitis [18]. The contrast enhanced technique is more relevant in the older population.
Intravenous contrast material has been shown to aid in the diagnosis of appendicitis by permitting the identification of the inflamed appendix. This may be critical in patients with mild appendicitis and a paucity of mesenteric fat, and in those with perforated appendicitis [2, 3]. Opacification of the terminal ileum and caecum with oral contrast material has been advocated to avoid false positive results, in which fluid filled terminal ileal loops are misdiagnosed as distended, inflamed appendices [4]. Moreover, opacification of the normal appendix serves to exclude appendicitis.
Identification of the normal appendix effectively excludes appendicitis with a greater degree of confidence than does the inability to identify signs of appendicitis on CT. Lane et al [8] reported that 28 (67%) of 42 normal appendices were identified by using 5 mm, non-enhanced, helical CT; this finding was close to that of Weltman et al [13]. The more frequent identification of a normal appendix with 5 mm sections provided strong evidence to rule out acute appendicitis. In this study we identified normal appendix in 145 (77%) of 188 patients.
Adequate enteral opacification of ileocaecal bowel may take 45–60 min. To expedite scan acquisition, Rao et al [12] have promoted a focused appendiceal CT technique in which a limited helical CT study of the RLQ is performed after rapid administration of colonic contrast material. This technique has proved to be as accurate as those techniques in which iv and oral contrast material are administered, while allowing scanning completion within 15 min in the majority of patients examined. A limitation of this scanning method is that a minority of patients will require additional scanning of the proximal abdomen or of the distal pelvis to identify disease not included in the scanning field of view.
In another study, Funaki et al [15] evaluated the accuracy of unenhanced helical CT with enteric contrast material in the diagnosis of appendicitis in children and adults (n=100) treated at a community hospital. They found that focused, unenhanced helical CT with oral and rectal contrast material had outstanding sensitivity and specificity for the examination of both children and adults with suspected appendicitis.
Contrarily, Kamel et al [19] demonstrated the value of obtaining a CT scan of the abdomen and pelvis compared with obtaining a CT scan limited to the RLQ. The observed sensitivity in identifying patients in need of immediate surgery was 96% and would have decreased to 82% if scanning had been limited to the RLQ only. Of the 77 cases that were interpreted as negative for appendicitis at CT, 43 (56%) yielded alternative diagnoses, and 7 of these abnormalities would have been missed at focused CT because of their location. The four cases that were not appendicitis but necessitated immediate surgery were perforated duodenal ulcer, small bowel ischaemia, superior mesenteric venous thrombosis and incarcerated abdominal wall hernia. Kamel et al [19] concluded that 7 mm contrast enhanced CT of the abdomen and pelvis was more appropriate than a focused imaging approach of scanning only the RLQ.
The fastest CT protocol has been promoted by Lane et al [8, 9], who have advocated use of unenhanced helical CT of the entire abdomen and pelvis. This examination may be performed in 10 min, does not expose the patient to the potential risks associated with iodinated contrast agents, requires no bowel preparation, and represents the most cost effective imaging alternative to ultrasound. This procedure is most effective in patients with large body habitus, as diagnostic accuracy may be compromised in patients with little abdominal and intrapelvic fat [7, 8].
The prevalence of surgical excision of normal appendices can be reduced without increasing perforation rate, and unenhanced spiral CT findings can be used successfully and accurately to determine which patients have acute appendicitis. Unenhanced spiral CT may also be helpful in detecting diseases other than acute appendicitis in patients with acute pain in the lower abdomen [7].
In this study, CT scans obtained when patients presented with RLQ pain and the clinical impression was equivocal for appendicitis were evaluated. If no definite inflammatory changes are detected, on the basis of our experience we recommend that the patient be closely monitored for changes in clinical condition. Since our study results are highly accurate, we believe that thin section unenhanced helical CT is the optimal technique to detect acute appendicitis in adult patients.
Received for publication January 2, 2002. Revision received April 4, 2002. Accepted for publication May 23, 2002.
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