Retroperitoneal Solitary Fibrous Tumor: A "Patternless" Tumor.

Solitary fibrous tumor in the retroperitoneum is rarely found in the literature and to the best of our knowledge less than a hundred cases are described so far. Histopathological diagnosis is mostly based on a "patternless pattern" on microscopic examination, which is a storiform arrangement of spindle cells combined with a "hemangiopericytoma-like appearance" and increased vascularity of the lesion. Surgery is the mainstay of treatment and recurrence rates are generally low.