Carcinosarcoma, an atypical subset of gallbladder malignancies.

Carcinosarcoma represents an atypical subset of gallbladder malignancies, and sonographic imaging features have not yet been precisely defined. Previously reported cases have shown a heterogeneously echogenic solid mass protruding into and filling the gallbladder lumen. We present herein a case of carcinosarcoma and propose another finding suggestive of this tumor. The patient was a woman in her 70s. Abdominal sonography revealed that the gallbladder lumen was half-filled by a large mass (maximum diameter, 68 mm) showing heterogeneous echogenicity slightly higher than that of bile. However, despite the large size of the mass, gallbladder shape was well-preserved. Considering the findings on computed tomography, cholecystectomy was performed under a diagnosis of gallbladder malignancy. Pathological examination revealed two types of malignant histology: a sarcomatous element of malignant spindle cells and a carcinomatous element of adenocarcinoma tissue. Foci of malignant cartilage and bone areas were also found sporadically. Accompanied by immunohistochemical examination, the mass was diagnosed as carcinosarcoma. The present case showed somewhat different imaging findings from those of ordinary gallbladder carcinoma. Carcinosarcoma should be considered when a well-preserved shape of the gallbladder is recognized along with protrusion of a large heterogeneously echogenic mass into and filling the gallbladder lumen.