Cholecystosonography in detection of acute cholecystitis: the halo sign--a significant sonographic finding.

To evaluate the efficacy of ultrasonography in detecting acute cholecystitis, we retrospectively reviewed the ultrasonic findings after cholecystectomy in 34 patients with acute cholecystitis and 90 patients with chronic cholecystitis. The sonographic findings evaluated included the length and width of the gallbladder, thickening of the gallbladder wall, good identification of the wall, and the presence or absence of sludge or stone. A "halo" sign (an echo-free space around the gallbladder wall) was seen in 26% of the patients with acute cholecystitis.