Ct

Accuracy of Nonfocused Helical CT for the Diagnosis of Acute Appendicitis: A 5-Year Review Steven S. Raman 1 David S. K. Lu 1 Barbara M. Kadell 1 Darko J. Vodopich 1 James Sayre 1 Henry Cryer 2

OBJECTIVE. The clinical usefulness of routine, nonfocused helical CT was evaluated in diagnosing acute appendicitis or providing an alternative diagnosis in patients presenting to the emergency department with acute lower abdominal pain. MATERIALS AND METHODS. We reviewed CT reports and clinical records of 650 consecutive adult patients who presented between January 1996 and December 2000 with right lower quadrant pain or lower abdominal pain and clinical findings suggestive of appendicitis. Helical CT was performed with oral contrast material in 610 cases (93.8%) and IV contrast in 572 cases (88.0%). Both vascular and enteric contrast media were administered in 544 cases (83.7%). Rectal contrast material was administered in 52 cases (8.0%). The abdomen was helically scanned from the dome of the diaphragm to the iliac crests with a collimation of 7 mm, from the iliac crests to the acetabular roof at a 5-mm collimation, from the acetabular roof to the symphysis pubis with a collimation of 5–10 mm. The surgical or clinical record was used for follow-up. RESULTS. Of the 650 patients, 552 (84.9%) had adequate clinical follow-up. There were 137 true-positive, eight false-positive, five false-negative, and 402 true-negative cases. The sensitivity, specificity, and accuracy of nonfocused helical CT were 96.5%, 98.0%, 97.6%, respectively. The positive and negative predictive values were 94.5% and 98.8%, respectively. In patients without acute appendicitis, CT suggested an alternative diagnosis, which clinically explained the patient’s acute abdominal pain in 266 patients (66.2%). CONCLUSION. Nonfocused helical CT was highly accurate in diagnosing acute appendicitis or suggesting an alternative diagnosis in patients with acute lower abdominal pain or right lower quadrant pain.

I

Received September 28, 2001; accepted after revision December 3, 2001. 1 Department of Radiology, UCLA Center for the Health Sciences, 10833 Le Conte Ave., Los Angeles, CA 900951721. Address correspondence to S. S. Raman. 2

Department of Surgery, UCLA Center for the Health Sciences, Los Angeles, CA 90095-1721. AJR 2002;178:1319–1325 0361–803X/02/1786–1319 © American Roentgen Ray Society

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n patients presenting to the emergency department, acute appendicitis is one of the most common causes of acute lower abdominal pain and right lower quadrant pain, and appendectomy is one of the most common surgical procedures in the Unitd States. However, the preoperative clinical diagnosis of appendicitis remains challenging even for experienced surgeons in 20–30% of the cases because myriad gastrointestinal, genitourinary, and gynecologic conditions can have similar presentations [1–3]. To avoid additional morbidity from missed or delayed diagnosis of acute appendicitis, surgeons have traditionally accepted that up to 20% of patients undergoing appendectomy for suspected acute appendicitis will have a normal appendix (negative appendectomy rate) [1]. A significant number of patients without acute appendicitis who have equivocal clinical presentations

could be spared the expense and morbidity of surgery by improved diagnosis with judicious use of preoperative imaging. Conversely, patients with atypical presentations of acute appendicitis could be spared the morbidity associated with missed or delayed diagnosis [4]. CT has excellent reported sensitivity and accuracy in the preoperative diagnosis of acute appendicitis [5–14] and acute abdominal pain [15, 16]. However, controversy persists about the role of CT in the diagnosis of appendicitis and the most effective techniques of examination [17]. A variety of CT approaches have been advocated including helical targeted or focused appendiceal techniques using rectal contrast agents (with or without oral contrast material) [5–7], unenhanced helical techniques similar to those used for the detection of renal stones [8–10],

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TABLE 1

Contrast Material Used in Helical CT of Patients with Right Lower Quadrant Pain or Lower Abdominal Pain

Type of Contrast Material Oral IV Oral and IV Rectal a Oral, IV, and rectal None a

Patients (n = 650) No.

%

610 572 544 52 41 10

93.8 88.0 83.7 8.0 6.3 1.5

All combinations.

IV contrast-enhanced techniques with supplementary cecal air insufflation [11], and routine contrast-enhanced (IV and oral) conventional and helical CT [12, 13]. The widespread applicability of some of these techniques in most practices is debated [13, 17] because some require the active participation of radiologists for patient triage [5, 6] and routinely subject patients to invasive procedures such as rectal catheterization [5–7, 11]. In addition to confirming suspected acute appendicitis, CT is valuable in excluding this diagnosis and in suggesting alternative diagnoses for acute abdominal pain. However, the rate at which CT suggests a clinically relevant alternative diagnosis to explain acute abdominal pain varies [5–16]. The purpose of this retrospective study was to review

Fig. 1.—True-positive interpretation in 27-year-old man with right lower quadrant pain. Axial contrast-enhanced helical CT scan shows that thickened appendix (>6 mm in width) and periappendiceal stranding (arrow) are present. Terminal ileum is well opacified. Secondary findings include appendiceal mural enhancement and cecal thickening.

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TABLE 2 Statistical Measure Sensitivity Specificity Accuracy PPV NPV

Success of Helical CT in Revealing Acute Appendicitis Results a 95% CI (%) %

No.

96.5 98.0 97.6 94.5 98.8

137/142 402/410 539/552 137/145 402/407

91.9–98.8 96.2–99.2 96.0–98.7 89.4–97.6 97.2–99.6

Note.—CI = confidence interval, PPV = positive predictive value, NPV = negative predictive value. a True-positive interpretation, n = 137; false-positive, n = 8; true-negative, n = 402; false-negative, n = 5.

our 5-year experience with routine, nonfocused helical CT in adults presenting with acute lower abdominal or right lower quadrant pain suspected of having acute appendicitis. Specifically, we evaluated the accuracy of routine, nonfocused helical CT in confirming a diagnosis of acute appendicitis or providing a clinically relevant true alternative diagnosis in this patient population. Materials and Methods With the approval from our institutional review board, we searched the databases of our radiology, surgery, and pathology departments to select all adult patients (≥18 years old) who were referred with symptoms of lower abdominal pain or right lower quadrant pain from January 1, 1996, through December 31, 2000. The indication for the examination as listed in the CT database was cross-referenced against each patient’s clinical chart to ensure the accuracy of the symptoms and satisfy the inclusion criteria for the study. During this period, approximately 69% of all patients with suspected acute appendicitis underwent appendectomy without CT. Approximately 31% of patients who underwent an appendectomy for suspected acute appendicitis also underwent preoperative abdominal CT, although the proportion steadily increased over 5 years. In general, most patients who underwent CT during this period were atypical in clinical presentation, because patients with clinical findings highly suspicious for appendicitis were taken to surgery without undergoing preoperative imaging. We excluded patients who had a history of appendectomy; patients who presented with atypical symptoms (right upper quadrant pain, back or flank pain, and left lower quadrant pain); patients with chronic abdominal pain; and patients with a known diagnosis of acute pancreatitis, cholecystitis, or diverticulitis before CT. We also excluded patients who underwent CT (interpreted as showing normal findings), were subsequently discharged from the emergency department and failed to return for a follow-up visit.

The combined search yielded 650 adult patients presenting with lower abdominal pain or right lower quadrant pain who underwent helical CT for possible acute appendicitis. Our study population consisted of 226 men and 424 women who ranged in age from 18 to 99 years; the average age was 49 years. The dictated CT reports were compared with the surgical, clinical, and pathologic records to establish clinical follow-up. Of the 650 patients, we had surgical and pathologic correlation in 191 patients (29.4%) and clinical correlation (clinical notes) in 361 (55.5%). Adequate clinical follow-up could not be obtained in 98 patients (15.1%) discharged from the emergency department because these patients failed to return for a follow-up clinic visit. These patients were excluded from the analysis. The overall population of patients evaluated for acute abdominal pain during this time is unknown. To our knowledge, no appendectomy was performed in any of our nonsurgical patients with clinical follow-up. All patients were scanned using a single-detector helical scanner (HiSpeed Advantage or HiSpeed CT/i; General Electric Medical Systems, Milwaukee, WI). Patients generally received both oral and IV contrast material. In this population, IV contrast material was administered in 88.0% of cases; poor renal function, contrast material allergy, or poor IV access precluded administration in the remainder. Oral contrast material was given in 93.8% of cases; nausea or other contraindications precluded use in the remainder. Both oral and IV contrast materials were given in 83.7% of cases. At the discretion of the attending radiologist or oncall radiology resident, rectal contrast material was given in 8.0% of cases. Contrast material was not administered in 1.5% of the cases (Table 1). In our standard protocol, patients generally drink 1000 mL of flavored 5% meglumine diazotrioate (Gastrografin; Bristol-Meyers Squibb, New Brunswick, NJ) 45–60 min before scanning to allow opacification of the ileum. After IV administration of 100– 130 mL of iohexol (Omnipaque 350; Nycomed, Princeton, NJ) at a rate of 2–3 mL/sec and after a 60sec delay, the abdomen was scanned helically during a single breath-hold (pitch of 1.4:1, 120–140 kVp, 240–320 mAs) with a 7-mm collimation to the iliac crests and a 5-mm collimation from the iliac crests to the acetabular roof. After a 3-min delay to allow opacification of the ureters and bladder, the remainder of pelvis to the symphysis pubis was scanned with a 5- to 10-mm collimation. Images were photographed, and a diagnosis was usually rendered on the basis of soft-copy images obtained using standard soft-tissue window settings (width, 400 H; level, 40 H). All interpretations were performed by radiologists specializing in abdominal imaging. Because of the retrospective nature of the study, we could not accurately account for discrepancies in interpretations between the on-call residents who worked after hours (7 P.M. to 7 A.M.) and the attendings. Therefore, the results of the dictated CT report were used as the official CT interpretation. The primary diagnostic criteria for acute appendicitis were vi-

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Helical CT of Acute Appendicitis

Fig. 2.—False-positive interpretation in 20-year-old man with right lower quadrant pain. On axial contrastenhanced helical CT scan, thickened appendix and mild adjacent stranding (arrow) are present. Patient’s symptoms resolved after medical therapy, and he was discharged.

sualization of a thickened appendix (distended appendix [width, >6 mm] with or without mural thickening and enhancement) and periappendiceal stranding (Fig. 1). Secondary diagnostic criteria included appendicolith, periappendiceal abscess, small-bowel obstruction, and mural thickening of the cecum. Cecal signs such as the cecal bar and cecal arrowhead were not evaluated because most patients did not receive rectal contrast material. For a case to be categorized as one with true-positive findings, the conclusion of the radiology report had to be the unequivocal diagnosis of acute appendicitis without offering a differential diagnosis. If acute appendicitis was reported and the pa-

tient did not undergo either an appendectomy or percutaneous drainage of a periappendiceal abscess or if the surgeon clinically excluded acute appendicitis, the case was categorized as a falsepositive. For a case to be categorized as a true-negative, the CT report must state that the scans were interpreted as showing either normal findings or findings that suggested an alternative diagnosis for acute abdominal pain, and acute appendicitis was not included in the differential diagnosis. In the false-negative category, we listed all cases for which CT was interpreted as showing normal or nondiagnostic findings and the patient had surgically proven appendicitis. We reviewed the scans for all cases categorized as true-positive, falsepositive, and false-negative to check for overcalled or missed findings. In patients without CT or clinical evidence of acute appendicitis (true-negatives), we compared the suggested alternative CT diagnosis with the clinical diagnosis in the computerized chart to determine whether the suggested CT diagnosis proved to be clinically relevant in explaining the patient’s abdominal pain.

Results

Overall, acute appendicitis was present in 142 (21.8%) of the 650 patients. Acute appendicitis was correctly diagnosed prospectively in 137 of 142 patients using routine helical CT (sensitivity, 96.5%) (Table 2). An appendectomy was performed in 130 of 137 patients. Of the remainder, five patients with periappendiceal abscesses were treated with percutaneous drainage without a follow-up appendectomy. In the other two patients, acute appendicitis was

Fig. 3.—False-positive interpretation in 71-year-old man with right lower quadrant pain. On axial contrast-enhanced helical CT scan, we misinterpreted cecal diverticulum (arrow) as thickened appendix. Cecal diverticulitis was confirmed at surgery.

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suspected clinically and treated medically with IV antibiotics because of comorbid conditions or refusal of surgery. Follow-up imaging was not performed in these patients. Acute appendicitis was correctly excluded prospectively in 402 patients (specificity, 98.0%). The overall accuracy was 97.6% for diagnosing acute appendicitis. No clinically relevant discrepancies in radiologic findings between the dictated CT reports and review of the studies were recorded. Of the eight false-positives, five patients were discharged after the presenting symptoms resolved, and three underwent surgery for suspected acute appendicitis. In one patient, both a thickened appendix and periappendiceal stranding were present, but the patient’s symptoms and physical examination findings resolved and the patient was subsequently discharged (Fig. 2). In the four other patients, fluid and various degrees of pericecal stranding were present in the right lower quadrant without a discrete appendix identified either prospectively or retrospectively. However, the symptoms resolved in these patients, and they were discharged. In these four cases, acute appendicitis was included in the differential diagnosis listed in the dictated CT report. In the first of three patients who underwent surgery, pericecal stranding was present on CT, and a prominent right cecal diverticulum was misinterpreted as a thickened appendix (Fig. 3). The second patient, a young woman with a surgically confirmed ruptured ovarian cyst, had

Fig. 4.—False-positive interpretation in 42-year-old man with right lower quadrant pain and surgically confirmed right-sided diverticulitis. Axial contrast-enhanced helical CT scan reveals focal region of stranding (arrow) adjacent to ascending colon. Appendix was not visualized, and acute appendicitis was included in differential diagnosis along with right-sided diverticulitis.

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Fig. 5.—False-negative interpretation in 34-yearold woman with lower abdominal pain. On axial contrast-enhanced CT scan, appendix (arrow ) is at upper limits of normal range in size without periappendiceal infiltration. Appendix was not identified prospectively, and study was interpreted as showing no evidence for appendicitis.

Fig. 6.—False-negative interpretation in 21-year-old woman with lower abdominal pain. On axial contrast-enhanced CT scan, appendix (arrow), which was identified only retrospectively, is at upper limits of normal range in thickness with minimal periappendiceal fat stranding. This study was initially interpreted as showing no evidence for appendicitis. Acute appendicitis was confirmed at pathology.

124 (90.5%) of 137 patients. No significant contrast material–related complications occurred in our study population. Of the true-negative cases, the alternative diagnosis based on CT findings agreed with the final clinical diagnosis in 266 (66.2%) of 402 patients without acute appendicitis (Figs. 8 and 9) (Table 3). Neither CT nor clinical findings explained the cause of acute abdominal pain in 108 (26.9%) of 402 patients. The CT diagnosis disagreed with the clinical impression in 28 patients (6.9%). Overall, a clinically relevant diagnosis for acute lower abdominal pain was provided in 403 (73%) of the 552 patients with adequate clinical follow-up. In the 98 patients with inadequate clinical follow-up, all CT findings were reported as unequivocal negative findings for appendicitis.

Discussion

mild pericecal stranding on CT. No discrete appendix was identified. CT of the third patient revealed a normal appendix and no findings to explain right lower quadrant pain (Fig. 4). At histopathology, “fibrous obliteration of the appendix” was noted in the report. False-negative CT findings were reported in five patients. In two patients, the appendix was within the upper limits of the normal range of thickness, and marginal periappendiceal stranding was identified retrospectively (Figs. 5 and 6). Scans of both patients were interpreted as showing “no evidence of acute appendicitis,” according to the CT report. The terminal ileum was not well opacified in either patient. In two other patients, neither primary nor secondary signs were iden-

tified prospectively or retrospectively. In these four patients, the pathologic cross-sectional diameter ranged between 6 and 8 mm. In the final patient with a false-negative finding, a high-grade small-bowel obstruction was identified prospectively. However, an appendiceal abscess, which was confirmed at surgery, had been misinterpreted prospectively on CT as the unopacified cecal base. However, even in retrospect, the abscess is difficult to detect (Fig. 7). A thickened appendix was visualized in 126 (92%) of the 137 patients with prospectively diagnosed appendicitis and likely in one of eight false-positive cases. Periappendiceal fat stranding was present in 135 (98.5%) of 137, and the combination of findings was present in

Fig. 7.—False-negative interpretation in 89-year-old woman with right lower quadrant pain. On axial contrast-enhanced CT scan, numerous asymmetrically dilated small-bowel loops are visible. Terminal ileum and cecum are poorly filled with contrast material. Periappendiceal abscess (arrows) was present but misinterpreted as base of unopacified cecum.

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In performing this study, we found that nonfocused contrast-enhanced helical CT of the abdomen and pelvis achieved high diagnostic accuracy in a large population of adult patients with acute lower abdominal pain or right lower quadrant pain and an average prevalence of acute appendicitis. Furthermore, we provided an alternate, clinically relevant explanation for acute abdominal pain in 66.2% of patients without appendicitis. Other studies have shown that CT is highly accurate in the evaluation of acute appendicitis, although debate continues about which technique is optimal [5–14, 17]. Before the report by Kamel et al. [13] was published, the best overall results were reported by Rao et al. [5, 6]; these researchers used focused CT of the lower abdomen after administration of a combination of oral and colonic contrast material [5] or colonic contrast material alone [6]. The two studies by Rao et al. were performed in a closely selected patient population who were actively triaged by experienced attending emergency radiologists. One study [6] included both children and adults with a strong clinical suspicion of acute appendicitis, and the researchers used sonography to exclude a large group of women with gynecologic disorders. In our study, all patients were adults who were referred at the discretion of emergency physicians or surgeons. At our center, most patients (69%) with strong clinical suspicion of acute appendicitis underwent an appendectomy without preoperative CT. We imaged only 31% of all patients who underwent

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Helical CT of Acute Appendicitis surgery for acute appendicitis, generally those presenting with acute lower abdominal pain but with a less certain clinical presentation of acute appendicitis. The overall prevalence of acute appendicitis was 53% in the study by Rao et al. [6] compared with 21% in our study population, a result that more closely reflects the expected prevalence of acute appendicitis in patients with acute lower abdominal pain [1, 2]. We included only adults, most of whom were female. Based on our experience, diagnosis of acute appendicitis in this subgroup causes the most clinical confusion, and CT is often requested for clarification. Despite the use of a general technique, a lack of patient selection, active triage, and inclusion of a majority of females, we achieved a diagnostic accuracy (97.6%) that is almost identical to that reported by Rao et al. (98%) [6]. Indeed, when applied to more typical referral cases in a community hospital setting with general board-certified radiologists, the reported performance of focused helical CT techniques was similar to those of other CT techniques [7]. One strength of the focused helical CT technique is the rate of detection of the appendix, reported to be as high as 100% [6]. In our series, the appendix was identified prospectively as being abnormal in 126 (92%) of the 137 patients with acute appendicitis. The appendix was identified as abnormal only on retrospective analysis in one of eight false-positive cases. We believe that in this patient, acute appendicitis may have been present and treated adequately with IV antibiotics. In the remaining seven patients, only various degrees of pericecal inflammation and fluid were present. A normal appendix was diagnosed in two of three patients who underwent surgery. In two patients, inflamed cecal diverticula were misinterpreted as acute appendicitis. Of the five false-negative cases, an appendix of normal width with minimal periappendiceal stranding was visualized retrospectively in two thin young women. In both patients, the pathology reports described early or minimal appendicitis. In two other patients, no findings were present to suggest acute appendicitis. Even on retrospective review, it is unclear whether thin-section CT would have added useful diagnostic information in these two false-negative cases or in the seven false-positive cases. In our series, colonic contrast material was used in only 8.0% of the cases, generally to better define cecal anatomy. In our retrospective review, the additional use of rectal contrast

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Fig. 8.—True-negative interpretation in 68-year-old woman with lower abdominal pain. On helical CT scan obtained using IV and oral contrast media, well-defined filling defect (arrow) is present in ileum. Lesion was confirmed on subsequent small-bowel barium examination. High-grade focal B-cell lymphoma was diagnosed at surgery.

Fig. 9.—True-negative interpretation in 28-year-old woman with lower abdominal pain and fever. On contrast-enhanced CT scan, patchy enhancement is visible bilaterally. Differential diagnosis included pyelonephritis, which was confirmed clinically.

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TABLE 3

Clinically Confirmed Alternate Diagnosis Suggested by Helical CT in Patients Without Acute Appendicitis Patients (n = 402)

Diagnosis No.

%

Colon Colitis Diverticulitis Fecal impaction Other

42 32 6 12

45.7 34.8 6.5 13

Total

92

22.9

Small bowel Small-bowel obstruction Inflammatory bowel disease Ischemia or infarction Other

38 15 6 14

52.1 20.5 8.2 19.1

Total

73

18.2

Gynecologic Ruptured adnexal cyst Adnexal mass Tuboovarian abscess Other

14 9 2 2

51.2 33.3 7.4 7.4

Total

27

6.7

Acute cholecystitis Acute pancreatitis Renal calculi passing Retroperitoneal hemorrhage Other

19 13 12 10 20

4.7 3.2 3.0 2.5 5.0

Total

266

66.2

material may have helped avoid a single falsenegative finding in an elderly woman. In this patient, an appendiceal abscess was misinterpreted as an unopacified cecum (Fig. 7). We agree with other researchers [13, 17] that administration of colonic contrast material is unnecessary to reach a conclusion in most patients, and we do not advocate its routine use. Moreover, patient tolerance of routine administration of rectal contrast material is debated [17]. The value of an alternative or focused helical CT examination has been questioned when applied to clinically equivocal cases of appendicitis because a wide range of gastrointestinal and genitourinary conditions can clinically mimic acute appendicitis [13, 15, 17]. In the studies by Rao et al. [5, 6] and Funaki et al. [7], most of the alternative diagnoses were restricted to the bowel and ileoce-

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cal mesentery. In the study by Kamel et al. [13], if the researchers had restricted imaging to the right lower quadrant, they would have significantly decreased the rate of alternative diagnoses, especially those requiring immediate surgery. In studies advocating unenhanced imaging, reported accuracy for diagnosing acute appendicitis has ranged from 93% for conventional CT [8] to 94–99% for helical CT [9, 10]. Although these studies have stressed the benefits of helical CT, which include lower cost and increased throughput, the rates of providing true alternative diagnoses were significantly lower (35–36%) [9, 10] than in our study and other studies that— with vascular or bowel contrast material or both—reported rates ranging from 54% to 95% [5–7, 11–16]. In our study, most patients received oral and IV contrast media, and we were able to provide a relevant alternative diagnosis for abdominal pain in 66.2% of patients without appendicitis (Table 3). This rate compares favorably with a rate of 56% reported by Kamel et al. [13]. In our experience and those of other researchers, the use of IV and oral contrast media is important to establish a diagnosis in patients with suspected acute abdomen [13, 15, 17]. The administration of contrast material in thin patients, particularly women, is needed to clearly identify the terminal ileum, smallbowel loops, and blood vessels. We present two cases in which the use of IV or oral contrast material helped to identify an alternative diagnosis (Figs. 8 and 9). We agree with Federle [17] that limited or focused studies unnecessarily restrict the ability to render a relevant diagnosis in patients with acute abdominal pain. Rhea et al. [18] have advocated the theory that routine focused appendiceal CT may lower both fixed and variable costs associated with caring for patients with appendicitis. Rao et al. [19] have advocated the theory that routine use of focused appendiceal CT reduces the use of hospital resources. However, focused techniques rely on expert interpretations and may not always provide a diagnosis for pain in patients with acute symptoms. Imaging every patient with suspected appendicitis may be impractical at many centers because readily available helical CT facilities and on-site radiologists experienced in interpretation of specialized examinations are required. This strategy would be particularly impractical at centers where residents and others with

variable CT experience often provide initial interpretations of images obtained of patients presenting after hours. We acknowledge several limitations to our study. Our study is retrospective, and the types of helical scanners, scan collimation, and contrast agents varied. However, we believe that this variability reflects the true clinical situation in most large radiology practices. We were unable to provide the true denominator of all patients evaluated for acute lower abdominal pain. We also could not obtain follow-up in 98 patients who were not diagnosed with acute appendicitis after CT and were discharged from the emergency department. We could not accurately account for discrepant interpretations between the on-call residents and those given by experienced abdominal imaging staff members for examinations performed at night. Because the interpretations were those of experienced abdominal radiologists, widespread general applicability may be somewhat limited. Also, the scans with true-negative findings were not retrospectively reviewed. In summary, we found that routine contrastenhanced helical CT is an excellent diagnostic test to define the cause of acute lower abdominal pain in adult patients with suspected acute appendicitis. The study cohort was large, unselected, and likely reflects the population of a large radiology practice. We also advocate the judicious use of routine contrast-enhanced CT (oral and IV media) to help establish a diagnosis in adults with an equivocal clinical presentation of acute appendicitis. References 1. Berry J Jr, Malt RA. Appendicitis near its centenary. Ann Surg 1984;200:567–575 2. Lewis FR, Holcroft JW, Boey J, et al. Appendicitis: critical review of 1000 patients. Arch Surg 1975;110:677–684 3. Bongard F, Landers DV, Lewis F. Differential diagnosis of appendicitis and pelvic inflammatory disease. Am J Surg 1985;150:90–96 4. Eldar S, Nash E, Sabo E, et al. Delay of surgery in acute appendicitis. Am J Surg 1997;121:312–317 5. Rao PM, Rhea JT, Novelline RA, et al. Helical CT technique for the diagnosis of appendicitis: prospective evaluation of a focused appendix CT examination. Radiology 1997;202:139–144 6. Rao PM, Rhea JT, Novelline RA, Mostafavi AA, Lawrason JN, McCabe CJ. Helical CT combined with contrast material administered only through the colon for imaging of suspected appendicitis. AJR 1997;169:1275–1280 7. Funaki B, Grosskreutz SR, Funaki CN. Using unenhanced helical CT with enteric contrast material for suspected appendicitis in patients treated at a

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Helical CT of Acute Appendicitis community hospital. AJR 1998;171:997–1001 8. Malone AJ Jr, Wolf CR, Malmed AS, Melliere BF. Diagnosis of acute appendicitis: value of unenhanced CT. AJR 1993;160:763–766 9. Lane MJ, Katz DS, Ross BA, Clautice-Engle TL, Mindelzun RE, Jeffrey RB Jr. Unenhanced helical CT for suspected acute appendicitis. AJR 1997;168:405–409 10. Lane MJ, Liu DM, Huynh MD, Jeffery RB Jr, Mindelzun RE, Katz DE. Suspected acute appendicitis: nonenhanced helical CT in 300 consecutive patients. Radiology 1999;213:341–346 11. Stroman DL, Bayouth MD, Kuhn JA, et al. The role of computed tomography in the diagnosis of acute appendicitis. Am J Surg 1999;178:485–488

12. Balthazar EJ, Megibow AJ, Siegel SE, Birnbaum BA. Appendicitis: prospective evaluation with high-resolution CT. Radiology 1991;180:21–24 13. Kamel IR, Goldberg SN, Keogan MT, Rosen MP, Raptopoulos V. Right lower quadrant pain and suspected appendicitis: nonfocused appendiceal CT—review of 100 cases. Radiology 2000;217: 159–163 14. Choi YH, Fisher E, Hoda SA, et al. Appendiceal CT in 140 cases: diagnostic criteria for acute and necrotizing appendicitis. Clin Imaging 1998;22: 252–271 15. Siewart B, Raptopoulos B, Mueller MF, Rosen MP, Steer M. Impact of CT on diagnosis and management of acute abdomen in patients initially treated

without surgery. AJR 1997;168:173–178 16. Taourel P, Baron MP, Pradel J, Fabre JM, Seneterre E, Bruel JM. Acute abdomen of unknown origin: impact of CT on diagnosis and management. Gastrointest Radiol 1992;17:287–291 17. Federle MP. Focused appendix CT technique: a commentary. Radiology 1997;202:20–21 18. Rhea JT, Rao PM, Novelline RA, McCabe CJ. A focused appendiceal CT technique to reduce the cost of caring for patients with clinically suspected appendicitis. AJR 1997;169:113–118 19. Rao PM, Rhea JT, Novelline RA, Mostafavi AA, McCabe CJ. Effect of computed tomography of the appendix on treatment of patients and use of hospital resources. N Engl J Med 1998;338:141–146

The full text and images from the American Journal of Roentgenology may also be viewed online at www.arrs.org or www.ajronline.org.

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