Gastrointestinal: Solitary fibrous tumor

Abstract

A woman, aged 67, was referred for evaluation because of a mass in the left upper quadrant of her abdomen. She had noted intermittent discomfort in the region for the preceding 6 weeks. There were no other significant gastrointestinal symptoms. On examination, the mass was firm and extended for approximately 5 cm below the left costal margin. A contrast-enhanced computed tomography scan showed a mass, 13 cm in diameter, in the region of the lesser sac. The mass was predominantly of low density and had unusual internal septations (Fig. 1). The stomach was displaced anteriorly and to the right while the pancreas was displaced inferiorly. The differential diagnosis included a stromal cell tumor and sarcomas arising from the stomach, pancreas or mesentery. A barium meal radiograph was consistent with external compression of the stomach (Fig. 2). At laparotomy, a large neoplasm was removed along with the spleen and the tail of the pancreas. Histological evaluation revealed an encapsulated tumor composed of spindle cells, bands of fibrous tissue and areas of cystic degeneration. Immunohistochemical studies were positive for CD34 and bcl2 and negative for a variety of proteins including CD117 and S-100. The pathological diagnosis was that of a solitary fibrous tumor arising from the retroperitoneum. Solitary fibrous tumors are well circumscribed neoplasms with spindle cell fibrous and myofibroblastic proliferation separated by strip-like bands of collagen. They have mostly been described in the pleura but extrapleural sites include the peritoneum, retroperitoneum and mediastinum. Most of the tumors including the case described above have low mitotic rates and are considered benign. In a minority of cases, however, the neoplasms have high cellularity and high mitotic rates that are associated with higher risks for local recurrence and metastases. Immunohistochemical studies are helpful for differentiating solitary fibrous tumors from stromal cell tumors, smooth muscle tumors and benign neural tumors. The characteristic feature for solitary fibrous tumors is expression of an antigen recognized by CD34, a feature that occurs in at least 90% of specimens. Contributed by