Pope’s hat sign: another valuable CT finding of early acute cholecystitis

Purpose: To determine the diagnostic performance of minor computed tomography (CT) findings for acute cholecystitis and demonstrate the incremental benefit of pope’s hat sign as an additional minor CT finding in patients suspected to have early acute cholecystitis. Materials and Methods: Two radiologists reviewed CT scans of 116 patients with early acute cholecystitis and 116 control patients. All cases in the patient group were surgically proven to have acute cholecystitis and preoperative dynamic CT scans. Evaluated CT parameters included major criteria (gallstone, distension of gallbladder (GB) lumen, GB wall edema, pericholecystic fat infiltration, and pericholecystic fluid collection) and minor criteria (GB bed hyperemia, tensile GB fundus sign, hyperdense GB wall sign, increased bile attenuation within GB, and pope’s hat sign). Results: In a univariate analysis, among the minor criteria, GB bed hyperemia, tensile GB fundus sign, increased bile attenuation within GB, and pope’s hat sign were more frequently observed (P < 0.05) in the early acute cholecystitis group. The optimal cut-off value of GB distension for discriminating between the two groups was 3.05 cm. In a multivariable analysis, GB bed hyperemia, pope’s hat sign, and GB lumen > 3.05 cm were significant findings for differentiating the two groups (P < 0.001). Among all combinations of these findings, the combination of GB bed hyperemia and pope’s hat sign exhibited the highest specificity (96.5%) and the combination of all three findings showed the highest sensitivity (94.0%). Conclusion: Pope’s hat sign is a new finding that could improve CT diagnostic performance for early acute cholecystitis in patients with RUQ pain in the emergency department. The combination of pope’s hat sign with GB bed hyperemia or GB lumen distension > 3.05 cm may be even more helpful in the early stage or in mild forms of acute cholecystitis.