Leiomyoma of the gallbladder in a patient with metastatic gastrointestinal stromal tumor in the liver: A case report with differential diagnostic considerations.

Mesenchymal tumor of the gallbladder is rare and the majority of cases present as sarcomas. Benign mesenchymal tumors of the gallbladder are extremely rare and to date, only one case of leiomyoma has been reported. In this report, we describe a second case of leiomyoma of the gallbladder, and discuss the differential diagnostic considerations. A 55-year-old female with metastatic gastrointestinal stromal tumors (GISTs) in the liver was identified to possess a tumorous lesion of the gallbladder. The patient had previously received a partial gastrectomy for GIST, and multiple liver metastases were revealed. Following surgery, imatinib was administered, and the liver metastatic lesions were stabilized. Histopathological analysis of the resected gallbladder specimens revealed that the nodule arose from the muscular layer, and was composed of spindle cell proliferation with eosinophilic cytoplasm and bland cigar-shaped nuclei. Mitotic figures were rarely noted, and necrosis was not observed. Immunohistochemical analyses demonstrated that the tumor cells were positive for desmin and alpha-smooth muscle actin, but negative for CD117 and CD34. In accordance with these results, a final diagnosis of leiomyoma of the gallbladder was made. The present case is unique since the patient possessed multiple metastatic GISTs in the liver, and the gallbladder nodule was preoperatively suspected to be a metastatic GIST. Leiomyoma of the gallbladder is extremely rare; however, it may be an underrecognized entity. Thus, it is important to differentiate leiomyoma from GIST to avoid unnecessary clinical follow-up and treatment.