Actinomycosis of the gallbladder mimicking carcinoma: a case report with US and CT findings

Abstract

We describe a case of actinomycosis of the gallbladder mimicking carcinoma. Sonography showed a hypoechoic mass replacing gallbladder lumen and engulfing a stone; contrast-enhanced computed tomography showed a heterogeneously enhanced thickened gallbladder wall with subtle, disrupted luminal surface enhancement, which formed a mass. As a result of the clinical and radiologic presentation, our impression was of gallbladder carcinoma. Actinomycosis should be included in the differential diagnosis when sonography and computed tomography findings show a mass engulfing the stone in the gallbladder and extensive pericholecystic infiltration with extension to neighboring abdominal wall muscle.

Fig. 1

A 65-year-old man with actinomycosis of the gallbladder which presented as a mass. A. Sonograph shows a hypoechoic mass (arrows) replacing gallbladder lumen and engulfing a gallstone with infiltration of surrounding liver. B. Unenhanced CT scan shows the impacted gallstone (arrow) and calcification (arrowhead) in the thickened gallbladder wall. The other gallstone is in the neck of the gallbladder (not shown). C. Contrast-enhanced CT scan obtained during the arterial phase at the same level as B, shows a heterogeneously enhanced and markedly thickened gallbladder wall (arrows) with infiltration of surrounding liver, stomach, and pericholecystic fatty tissue. Faint, disrupted luminal surface enhancement around the stone (asterisk) and hepatic parenchymal enhancement (arrowhead) adjacent to the thickened gallbladder wall are evident. S = stomach. D. Contrast-enhanced CT scan obtained during the portal phase at a level 1 cm below C shows disrupted luminal surface enhancement of the thickened gallbladder wall (arrowhead) with pericholecystic fatty infiltration, perihepatic extension of the soft tissue mass (arrows), and mild thickening of the transversus abdominis muscle (asterisk). E. Photograph of the cut surface of the resected gallbladder shows markedly thickening of gallbladder body and fundus walls and a fibrotic appearance. Two brown stones (arrows) are indicated. F. Photomicrograph of the thickened gallbladder wall shows inflammatory cell infiltration with fibrosis, and a sulfur granule (arrow) containing tangled filamentous bacilli, which is compatible with Actinomyces. (H & E stain, × 400).