Abstract
A 46-year-old woman with positive fecal occult blood during medical examination visited our hospital for further endoscopic examination. An abdominal tumor was suspected on palpation. Upper and lower gastrointestinal endoscopy showed no significant abnormalities. However, abdominal CT scan revealed a giant mass in the right retroperitoneum highly suggestive of gastrointestinal stromal tumor (GIST) originating from the duodenum. The resected tumor measured 135 × 127 × 55 mm in diameter and had a pseudocapsule with no connection with the duodenum. Histological examination showed proliferation of closely packed spindle epithelioid cells, and KIT (++), CD 34 (-), and SMA (++) by immunostaining, suggesting a diagnosis of GIST. Pathological re-examination of the tumor showed negative DOG1 and positive HMB45 immunostaining which excludes GIST from the diagnosis. A growth of epithelioid cells similar to lymphangioleiomyomatosis (LAM) was found in the lymph nodes around the tumor. Simultaneously performed chest HRCT showed a thin-walled, air-filled cyst, which was consistent with pulmonary LAM. The retroperitoneal tumor, unlike true LAM, was diagnosed as perivascular epithelioid tumor because of having a malignant potential owing to its size and focal necrosis with hemorrhage.
