Hyperechoic Periappendiceal Fat: Evaluation of Criteria for Improving Specificity in the Sonographic Diagnosis of Appendicitis in Pediatric Patients.

OBJECTIVES: To test the hypothesis that abutting and encasing types of hyperechoic periappendiceal fat are specific sonographic indicators of appendicitis in pediatric patients, including individuals with maximum outer diameters (MODs) of 6 to 8 mm in whom diagnosis by the MOD alone is known to be equivocal. METHODS: Appendiceal sonograms of 271 consecutive pediatric patients were retrospectively evaluated for hyperechoic periappendiceal fat (globular, ≥1.0 cm; categorized as type 0, none; type 1, "abutting," encompassing <180° of the appendiceal circumference; or type 2, "encasing," encompassing 180° or more of the appendiceal circumference) and the MOD. Histopathologic and medical records constituted reference standards. Statistical methods included the binomial distribution, logistic regression, a receiver operating characteristic analysis, and the exact McNemar test. RESULTS: All patients with hyperechoic fat and 105 of 107 patients with appendicitis had MODs of 6 mm or greater. The MOD and fat types 1 and 2 each were significantly associated with appendicitis in the univariable regression. The MOD and fat type 1 were independently associated with appendicitis in multivariable regression (odds ratio, 24.97; P = .034; and odds ratio, 5.35; P < .001, respectively). Specificities of an MOD of 6 to 8 mm and an MOD of 6 mm or greater alone were 89.0% (95% confidence interval, 83.2%-93.4%); these increased to 100.0% each (95% confidence interval, 97.8%-100.0%; P < .001) when combined with fat types 1, 2, and either 1 or 2 as diagnostic criteria, with positive predictive values of 100.0%. CONCLUSIONS: Types 1 and 2 periappendiceal fat are specific indicators of appendicitis, and both improve specificity compared to the MOD. Importantly, they add specificity in diagnosing appendicitis in patients with diagnostically equivocal MODs of 6 to 8 mm.

The Borderline-Size Appendix: Grayscale, Color Doppler, and Spectral Doppler Findings That Improve Specificity for the Sonographic Diagnosis of Acute Appendicitis.

Diagnostic criteria for acute appendicitis using graded compression sonography have been well established based on the maximum outer diameter (MOD) of the appendix, with MOD values of <6 mm nearly always indicating normal appendices and MOD values of >8 mm nearly always indicating appendicitis. However, the "borderline-size" appendix, meaning one whose MOD lies between these ranges (ie, an appendix with MOD of 6-8 mm), presents a diagnostic dilemma because appendices in this size range are neither clearly normal nor abnormal when diagnosis is based on the MOD alone; accordingly, such borderline MOD values are diagnostically equivocal, and sonographic diagnosis must rely on sonographic findings other than the MOD. The goal of this review was to examine the additional sonographic findings that can add specificity and help enable an accurate diagnosis to be made in patients with borderline-size appendices.

Ileocolic vascular curvature: a new CT finding of cecal volvulus.

PURPOSE: To evaluate the diagnostic performance of a proposed new CT observation in cecal volvulus, marked hook-like curvature of ileocolic vessels termed "ileocolic vascular curvature." METHODS: Contrast-enhanced CT scans of 14 patients with diagnoses of cecal volvulus on original CT reports were compared with scans of 40 control patients with dilated cecum but no cecal volvulus on original CT reports, accrued consecutively from January, 2006 through July, 2017. Two independent blinded readers retrospectively evaluated scans for cecal dilatation, ileocolic vascular curvature and seven previously reported CT features of cecal volvulus. Statistical methods included the exact binomial distribution to define 95% confidence intervals (95% CIs), logistic regression, receiver operating characteristic analysis, and the exact McNemar test. Pathology reports and clinical records served as reference standards. RESULTS: All patients had abdominal pain and cecal distension. All 14 patients with CT diagnoses of cecal volvulus, and no control patients, had cecal volvulus by reference standards. Ileocolic vascular curvature and ectopic cecal location were the only features independently and significantly associated with cecal volvulus in multivariable regression (odds ratio 178, p = 0.014, and 63, p = 0.013, respectively) and also the only features with both sensitivity (12/14 [85.7%, 95% CI 57.2-98.2%] and 13/14 [92.9%, 95% CI 66.1-99.8%], respectively) and specificity (40/40 [100.0%, 95% CI 91.2-100.0%] and 38/40 [95.0%, 95% CI 83.1-99.4%], respectively) that differed significantly from 50.0%. CONCLUSIONS: Ileocolic vascular curvature was independently and significantly associated with cecal volvulus and exhibited both substantial sensitivity and substantial specificity for cecal volvulus, and thus is potentially a valuable new CT finding of cecal volvulus.

Groove pancreatitis: a clinical and imaging overview.

Groove or paraduodenal pancreatitis is an uncommon fibroinflammatory form of pancreatitis involving the anatomic space of the pancreatic groove located between the C-loop of the duodenum and the head of the pancreas. Although in some patients there are distinctive clinical and imaging features of groove pancreatitis (GP), there is often significant overlap with other infiltrative processes involving the pancreatic groove such as pancreatic ductal adenocarcinoma or duodenal carcinoma. In this review, we summarize the most distinctive clinical and imaging aspects of GP and highlight some important distinguishing features that may aid in differentiating malignant lesions involving the pancreatic groove.

Hyperechoic Abdominal Fat: A Sentinel Sign of Inflammation.

One of the most useful sonographic signs of acute abdominal inflammation is the identification of increased echogenicity of the surrounding fat. Hyperechoic fat results from vasodilation and edema extending from an adjacent source of infection or inflammation. These changes are mediated by such factors such as bradykinin, histamine, and various cytokines. The recognition of hyperechoic fat on sonography may be an important indicator of the primary source of pathology. In addition, it often reflects a more advanced degree of transmural pathology, such as "walled-off" perforation of a hollow viscus. This pictorial essay will present a variety of examples of hyperechoic inflamed fat involving different abdominal organs and will illustrate the diagnostic value of this finding.

Luminal obstruction in uncomplicated appendicitis: Detection with sonography and potential clinical implications.

PURPOSE: To determine the frequency of luminal obstruction on appendiceal graded compression sonography (US) in patients with uncomplicated appendicitis and test the hypothesis that this frequency is similar to the failure rates of primary antibiotic therapy for uncomplicated appendicitis when treatment selection is based on CT findings. METHODS: Sonograms of 150 consecutive patients with appendicitis diagnosed on ultrasound (US) and proven histopathologically were retrospectively evaluated; 114 (76.0%) had uncomplicated appendicitis, that is, appendicitis without gangrene or perforation, and were evaluated for appendicolithiasis and lymphoid hyperplasia using previously published sonographic criteria, and for luminal obstruction. RESULTS: Of the 114 patients with uncomplicated appendicitis, US demonstrated no luminal obstruction in 74 (64.9%) and luminal obstruction in 40 (35.1%, P = .018), the latter including 16 (40.0%) with lymphoid hyperplasia and 24 (60.0%, P = .074) with appendicolithiasis. CONCLUSIONS: US demonstrated luminal obstruction in 35.1% of patients with uncomplicated appendicitis, similar to the published failure rates of antibiotic therapy when treatment selection is based on CT. This confirms the hypothesis, supporting the possibility that undiagnosed luminal obstruction may account for treatment failures when patients are selected by CT for primary antibiotic therapy, and suggests a role for US in selecting patients without luminal obstruction for antibiotic therapy.

Sonography of the Cecum: Gateway to the Right Lower Quadrant.

Sonography of the cecum has come of age largely as a consequence of the successful evolution of appendiceal sonography as a useful tool in the evaluation of patients with right lower-quadrant pain. At some medical centers, graded-compression sonography (GCS) has become the initial imaging study of choice in the assessment of these individuals. The cecum serves as a helpful anatomic landmark for localization of the appendix in these examinations-providing a sonographic starting point in the search for the appendix. During GCS, primary pathology within the cecum itself can become evident, including a variety of processes, such as infectious, inflammatory, or neoplastic disorders, whose presentations commonly mimic that of appendicitis. The accurate diagnosis of cecal abnormalities and their differentiation from acute appendicitis play valuable roles in the management of affected patients because the options for further workup and subsequent treatment vary greatly according to the diagnosis at hand. Additionally, the compressed cecum often becomes an acoustic window into the right lower quadrant, revealing pathology apart from the appendix within the right iliac fossa. The purpose of this pictorial essay is to highlight the importance and value of performing a careful evaluation of the cecum during GCS of patients with suspected appendicitis and to review the differential diagnosis and imaging findings of primary cecal abnormalities whose clinical presentations can mimic that of acute appendicitis.

Duodenal invasion by pancreatic adenocarcinoma: MDCT diagnosis of an aggressive imaging phenotype and its clinical implications.

Despite advances in oncologic and imaging technology, pancreatic ductal adenocarcinoma remains a highly deadly disease. The only curative option, pancreaticoduodenectomy or pancreatectomy, carries a significant morbidity. Current imaging plays a role in pre-operative staging to determine the probability of achieve disease-free margins. However, a small but not insignificant number of pancreatic cancers have a relatively higher aggressive biology, despite being resectable based on traditional criteria. Recently, imaging biomarkers that serve as a surrogate for tumors with such aggressive phenotype have been described. These include duodenal invasion and extrapancreatic perineural invasion. This review will focus on the former highlighting the summary of literature supporting duodenal invasion as a surrogate for aggressive disease as well as review its MDCT imaging features.

Anatomic Reasons for Failure to Visualize the Appendix With Graded Compression Sonography: Insights From Contemporaneous CT.

OBJECTIVE: The purpose of this study is to identify the anatomic locations of appendixes on CT when graded compression sonography fails to visualize the appendix. MATERIALS AND METHODS: The study included 197 patients with suspected appendicitis whose appendixes were not visualized on graded compression sonography performed with typically used transducers of at least 10 MHz, who underwent CT within 48 hours following graded compression sonography, and who had available either pathologic examination following surgery or 6-week follow-up if surgery was not performed. Appendixes were retrospectively localized using four transverse quadrants (including the posteromedial quadrant) centered on the ileocecal valve and projected vertically, the craniocaudal level relative to the iliac crests, and the depth of the appendix as measured from the surface of the skin. Data were assessed using the Fisher exact test, t test, multinomial test, binomial distribution, ANOVA, and linear regression. RESULTS: Appendixes were most frequently located in the posteromedial quadrant (123 of 197 patients [62.4%]; 95% CI, 55.3-69.2%) at a statistically significantly greater frequency than that expected by chance (p < 0.00001). Appendixes were located above the iliac crests in 19.8% of patients (39/197; 95% CI, 14.5-26.1%) and at depths exceeding the penetration of typical transducers of at least 10 MHz in 19.3% of patients (38/197; 95% CI, 14.0-25.5%). All appendixes (95% CI, 98.1-100.0%) were located within the range of 6-MHz transducers. CONCLUSION: Appendixes that are not visualized on graded compression sonography are most frequently located in the posteromedial quadrant and are often located above the iliac crests or at depths too great for visualization with typically used transducers of at least 10 MHz. Accordingly, when the appendix is not visualized on graded compression sonography, targeted scanning of the posteromedial quadrant and the region above the iliac crests, and scanning with 6-MHz transducers, may enable visualization of the appendix and are recommended additions to scanning protocols.

Spectral Doppler Waveforms for Diagnosis of Appendicitis: Potential Utility of Point Peak Systolic Velocity and Resistive Index Values.

Purpose To test the hypothesis that appendiceal spectral Doppler waveforms can distinguish patients with and patients without appendicitis. Materials and Methods In this retrospective study, Doppler waveforms were obtained from intramural appendiceal arteries identified with color Doppler imaging in 60% (93 of 155) of consecutive patients whose appendices were visualized at graded compression ultrasonography (US) performed for suspected appendicitis (53 male and 40 female; age, 1-56 years; mean, 14.5 years) over the 5-month period from November 2015 through March 2016. Point, non-angle-corrected peak systolic velocity (PSV) and resistive index (RI) values were compared between patients with and patients without appendicitis by utilizing histopathologically proven appendicitis and 6-week clinical follow-up as diagnostic reference standards. Data were assessed by using the Student t test, exact binomial distribution, two-sample test of proportions, and receiver operating characteristic analysis. Results Among the 93 patients, 36 (38.7%) had proven appendicitis (mean PSV, 19.7 cm/sec; mean RI, 0.69) and 57 patients (61.2%) did not (mean PSV, 7.1 cm/sec, P < .0001; mean RI, 0.50, P < .0001). The area under the receiver operating characteristic curve for the diagnosis of appendicitis was 0.97 (95% confidence interval [CI]: 0.95, 1.00) for PSV and 0.86 (95% CI: 0.78, 0.95; P = .011) for RI. Chosen discriminatory criteria of PSV greater than 10 cm/sec and RI greater than 0.65 yielded specificity for appendicitis of 94.7% and 96.5% with sensitivity of 88.9% and 63.9% (P = .013) and negative predictive value of 93.1% and 80.9% (P = .045), respectively. Original clinical graded compression US interpretations based on established US findings demonstrated specificity of 96.2% and sensitivity of 100.0%. Considering the subset of 20 patients whose maximum outer diameter measured 6-8 mm, the discriminatory criteria of PSV greater than 10 cm/sec and RI greater than 0.65 yielded specificity for appendicitis of 88.9% each, with sensitivity of 100.0% and 63.6% and negative predictive value of 100.0% and 66.6%, respectively. Conclusion In patients with visualized appendices at US, those with appendicitis exhibit significantly higher point PSV and point RI values than do patients without appendicitis and are distinguishable with high specificity by using a PSV greater than 10 cm/sec and an RI greater than 0.65 as diagnostic criteria. © RSNA, 2017.

Sonographic Differentiation of Complicated From Uncomplicated Appendicitis: Implications for Antibiotics-First Therapy.

OBJECTIVES: To evaluate sonographic findings as indicators of complicated versus uncomplicated appendicitis in the setting of known appendicitis, a necessary distinction in deciding whether to proceed with antibiotic therapy or with appendectomy. METHODS: With Institutional Review Board approval and Health Insurance Portability and Accountability Act compliance, appendiceal sonograms of 119 patients with histopathologically proven appendicitis were retrospectively blindly reviewed to determine the presence or absence of the normally echogenic submucosal layer, the presence of mural hyperemia, periappendiceal fluid, appendicoliths, and hyperechoic periappendiceal fat and to determine the maximum outside diameter. Results were compared with the presence of complicated versus uncomplicated appendicitis on histopathologic examination and assessed by both univariate and mulitvariate logistic regression; confidence intervals (CIs) of proportions were assessed by the exact binomial test. RESULTS: Thirty-two (26.9%) of the 119 patients had complicated appendicitis, including 11 with gangrenous appendicitis without perforation and 21 with gangrenous appendicitis and perforation. Loss of the submucosal layer was the only independent significant indicator of complicated appendicitis in multivariate regression (P < .001) and provided sensitivity and specificity values of 100.0% (95% CI, 89.1%-100.0%) and 92.0% (95% CI, 84.1%-96.7%), respectively. CONCLUSIONS: Loss of the normally echogenic submucosal layer was the most useful sonographic finding for discriminating complicated from uncomplicated appendicitis, being the only finding independently and significantly associated with complicated appendicitis and, additionally, providing both high sensitivity and high specificity. This information may help a physician decide whether to proceed with antibiotic therapy or with appendectomy when treating a patient with appendicitis.

Delayed diagnosis of celiac stenosis causing hepatic transplant ischaemic necrosis: diagnosis by spectral Doppler findings.

Following presentation with abnormal liver function enzymes, confusion and fatigue, a 65-year-old male with alcoholic cirrhosis underwent spectral Doppler sonography that showed tardus parvus-like morphology in the main and left hepatic arteries, although peak systolic velocities and resistive indices remained normal. The patient's continuing clinical symptoms prompted CT angiography, which demonstrated an unexpected, haemodynamically significant stenosis of the celiac artery. Although the stenosis was successfully stented and the hepatic arterial waveforms normalized, the transplanted liver had already undergone ischaemic necrosis, with resulting failure and the need for retransplantation. Recognition of abnormal waveforms, despite normal peak systolic velocities and resistive indices, with prompt definitive imaging evaluation of the arterial tree beyond just the main hepatic artery, may lead to the diagnosis of unexpected flow-limiting lesions in time to allow revascularization and thus prevent ischaemic transplant failure.

Multidetector CT imaging of the pancreatic groove: differentiating carcinomas from paraduodenal pancreatitis.

OBJECTIVE: This study aims to identify multidetector row CT (MDCT) findings that differentiate paraduodenal pancreatitis (PDP) from groove carcinomas (GC). METHODS: Two radiologists retrospectively reviewed various imaging features on pancreas protocol CT scans of 8 PDP and 8 GC patients. Two-tailed Fisher's Exact Test was used for statistical analysis. RESULTS: MDCT findings correlating with PDP included benign common bile duct morphology (P<.01), duodenal wall thickening (P<.05), and cystic groove lesions (P<.01). A statistical difference in gastroduodenal artery (GDA) encasement was not observed (P=.119). CONCLUSIONS: There are several MDCT findings that favor PDP over GC. However, presence of GDA encasement is not a reliable distinguishing feature.

Color Doppler Imaging of the Appendix: Criteria to Improve Specificity for Appendicitis in the Borderline-Size Appendix.

OBJECTIVES: To test the hypothesis that continuous intramural vascular signal measuring at least 3 mm on color Doppler imaging is highly specific for appendicitis in patients with diagnostically borderline-size appendices. METHODS: Two blinded observers independently reviewed color Doppler images of the appendix in 94 consecutive patients who had undergone sonography for suspected appendicitis and whose appendices were of diagnostically borderline size (6-8 mm maximum outer diameter). Intramural vascular flow on color Doppler images was classified as absent, type 1 (only punctate and dispersed signal), or type 2 (continuous linear or curvilinear signal measuring at least 3.0 mm in long- or short-axis views). Histopathologic examination and clinical follow-up served as reference standards. Proportions were assessed by the exact binomial test. RESULTS: Of the 94 patients, 33 (35.1%) had type 1 flow (of whom 5 [15.2%] had appendicitis); 23 (24.5%) had type 2 flow (of whom 20 [87.0%] had appendicitis); and 38 (40.4%) had absent flow (of whom 10 [26.3%] had appendicitis). The sensitivity, specificity, and odds ratio of type 2 flow as an indicator of appendicitis were 57.1%, 94.9%, and 24.9 (P< .001), respectively; the corresponding values for type 1 flow as an indicator of normal appendices were and 47.5%, 85.7%, and 5.4 (P = .002). CONCLUSIONS: Continuous intramural linear or curvilinear signal measuring at least 3 mm on color Doppler imaging is a highly specific, although relatively insensitive, sign of acute appendicitis in noncompressible appendices of diagnostically borderline size (6-8 mm).

Preoperative Multidetector CT Diagnosis of Extrapancreatic Perineural or Duodenal Invasion Is Associated with Reduced Postoperative Survival after Pancreaticoduodenectomy for Pancreatic Adenocarcinoma: Preliminary Experience and Implications for Patient Care.

Purpose To test the hypothesis that patients with pancreatic adenocarcinoma who otherwise are viewed to have resectable disease but have preoperative findings of extrapancreatic perineural invasion (EPNI) and/or duodenal invasion at multidetector computed tomography (CT) have reduced postoperative survival after pancreaticoduodenectomy for pancreatic ductal adenocarcinoma (PDAC). Materials and Methods This study was approved by the institutional review board and complied with HIPAA. The authors retrospectively evaluated 76 consecutive patients with PDAC who underwent preoperative multidetector CT and subsequent pancreaticoduodenectomy. Two radiologists blinded to surgical pathology results and clinical outcome evaluated multidetector CT images for evidence of EPNI and duodenal invasion; discrepancies were resolved by consensus. Also determined for each patient were resected lymph node status, tumor size, surgical margin status, time to progression, and time to death. Data were assessed with the Goodman-Kruskal gamma for correlations among indicators and the log-rank test, Kaplan-Meier estimates, and multivariate Cox proportional hazards regression for survival analysis. Results In univariate analysis, duodenal invasion and/or EPNI on preoperativemultidetector CT images was associated with significantly decreased progression-free survival (P < .0001) and overall survival (P = .0013), and the clinical indicators (lymph node status, tumor size, and surgical margin status) as well as duodenal invasion and/or EPNI showed correlation with each other. In multivariate regression that included multidetector CT findings as well as the three traditional clinical indicators, only duodenal invasion and/or EPNI showed significant independent association with reduction in both modes of survival (P < .0001 and P = .014, respectively). Interobserver agreement was substantial with respect to EPNI and duodenal invasion (κ = 0.691 and 0.682, respectively). Conclusion Patients with evidence of EPNI and/or duodenal invasion on preoperative multidetector CT images have significantly reduced survival after pancreaticoduodenectomy for PDAC. © RSNA, 2016.

Lymphoid Hyperplasia of the Appendix: A Potential Pitfall in the Sonographic Diagnosis of Appendicitis.

OBJECTIVE: The objective of this study was to test the hypothesis that thickening of the lamina propria, a finding produced by lymphoid hyperplasia, is significantly associated with false-positive sonographic diagnoses of appendicitis in 6- to 8-mm noncompressible appendixes. MATERIALS AND METHODS: Sonograms of 119 consecutive patients with suspected appendicitis and 6- to 8-mm noncompressible appendixes were retrospectively blindly evaluated for thickening of the lamina propria (short axis thickness ≥ 1 mm). The reference standard for appendicitis was pathologic analysis of resected specimens. Results were compared with the two-tailed Fisher exact test. RESULTS: Thirty-one patients (26.1%) had a thickened lamina propria and 88 (73.9%) did not. Of the 27 pediatric patients with a thickened lamina propria, five (18.5%) had true-positive and 22 (81.5%) had false-positive sonograms for appendicitis; among the 55 pediatric patients without a thickened lamina propria, 27 (49.1%) had true-positive and 28 (50.9%) had false-positive sonograms for appendicitis (p = 0.009). Similar differences in adult patients were not statistically significant. All five pediatric patients with appendicitis and thickened lamina propria also showed two or more findings of periappendiceal fluid, hyperechoic periappendiceal fat, or mural hyperemia on color Doppler examination, compared with two of 22 similar pediatric patients without appendicitis (p < 0.001). CONCLUSION: Lymphoid hyperplasia may result in a noncompressible appendix 6-8 mm in diameter and may be misdiagnosed as appendicitis in pediatric patients. True-positive diagnoses of appendicitis can be accurately identified by the presence of at least two additional findings from the group of periappendiceal fluid, hyperechoic periappendiceal fat, and mural hyperemia. Identifying the characteristic sonographic appearance of lymphoid hyperplasia may help prevent false-positive misdiagnoses of appendicitis.

MDCT Diagnosis of Perineural Invasion Involving the Celiac Plexus in Intrahepatic Cholangiocarcinoma: Preliminary Observations and Clinical Implications.

OBJECTIVE: The purpose of this study was to test the hypothesis that soft-tissue infiltration along the celiac plexus and delayed enhancement exceeding two-thirds of the tumor area on preoperative MDCT correlate with histologic evidence of perineural invasion in resected intrahepatic cholangiocarcinomas. MATERIALS AND METHODS: Two experienced abdominal radiologists retrospectively reviewed preoperative multiphasic MDCT scans of 20 patients who underwent resection of intrahepatic cholangiocarcinoma, identifying soft-tissue infiltration along the celiac plexus, delayed enhancement exceeding two-thirds of the tumor area, and maximum tumor diameter. Consensus findings were compared with intratumoral perineural invasion in resected intrahepatic cholangiocarcinomas using the Fisher exact test. RESULTS: Six patients had histologic intratumoral perineural invasion, five of whom had soft-tissue infiltration along the celiac plexus on preoperative MDCT, with corresponding 83.3% sensitivity and 92.9% specificity for perineural invasion and significant association between these MDCT and histologic findings (p = 0.002). No patients with histologic perineural invasion had enhancement exceeding two-thirds of the tumor area on MDCT; sensitivity was 0.0% for this finding. Tumor diameter on MDCT was not significantly associated with perineural invasion at histopathology (p = 0.530). CONCLUSION: Soft-tissue infiltration along the celiac plexus on MDCT is an indicator of perineural invasion in patients with intrahepatic cholangiocarcinoma. The data did not confirm an association between delayed enhancement exceeding two-thirds of the tumor area and perineural invasion. Because perineural invasion from intrahepatic cholangiocarcinoma is associated with a very poor prognosis and is generally a contraindication to surgery, the MDCT diagnosis of celiac plexus perineural invasion in patients with intrahepatic cholangiocarcinoma may have important implications for prognosis and treatment planning.

Journal Club: the Alvarado score as a method for reducing the number of CT studies when appendiceal ultrasound fails to visualize the appendix in adults.

OBJECTIVE. The purpose of this article is to evaluate the hypothesis that Alvarado scores of 3 or lower identify adult patients who are unlikely to benefit from CT after appendiceal ultrasound fails to show the appendix and is otherwise normal. MATERIALS AND METHODS. We identified 119 consecutive adults for whom the appendix was not seen on otherwise normal appendiceal sonography performed as the first imaging study for suspected appendicitis, who subsequently underwent CT within 48 hours, and whose data permitted retrospective calculation of admission Alvarado scores. Specific benefits of CT were defined as diagnoses of appendicitis or significant alternative findings, and specific benefits were compared between patients with Alvarado scores of 3 or less and 4 or higher. Significant alternative findings on CT were findings other than appendicitis that were treated with medical or surgical therapy during the admission or that were to be addressed during follow-up care. Diagnostic reference standards were discharge diagnoses, pathologic examinations, and clinical follow-up. RESULTS. No patients (0.0%, 0/49) with Alvarado scores 3 or lower had appendicitis, compared with 17.1% (12/70) of patients with Alvarado scores 4 or higher (p = 0.001), and CT showed neither appendicitis nor significant alternative findings in 85.7% (42/49) versus 58.6% (41/70) of these patients, respectively (p = 0.002). The rates of perforated appendicitis, as well as significant alternative CT findings, did not differ significantly. CONCLUSION. Adults with Alvarado scores 3 or lower who have nonvisualized appendixes and otherwise normal appendiceal sonography are at very low risk for appendicitis or significant alternative findings and therefore are not likely to benefit from CT.