An Unusual Solitary Fibrous Tumor of the Ischiorectal Region.

Solitary fibrous tumors (SFTs) are rare fibroblastic/myofibroblastic proliferations that occur in a wide range of anatomical sites. These tumors have nonspecific clinical presentations often with unpredictable biological behavior. SFTs can be slow growing low-risk tumors or rapidly growing high-risk tumors. They show a wide variety of histological features and typically are characterized by NAB2-STAT6 fusion. SFTs of the ischiorectal fossa are rare, with few studies reported in the literature to date. Here, we report a 90-year-old male who had a road traffic accident in October 2018. A pelvic computed tomography (CT) revealed a mass measuring 3.5 × 2.5 cm in the right ischiorectal fossa. Histopathology of the CT-guided biopsies confirmed the diagnosis of low-grade SFT. No surgical intervention was needed since the patient was asymptomatic. In January 2022, a follow-up CT showed a gradual increase in tumor size (5 × 3.5 × 3 cm), but not infiltrating the surrounding structures. However, the patient complained of constipation, which warranted a surgical excision of the mass. Subsequently, immunohistological examination reconfirmed the diagnosis of low-risk SFT. Here, we discussed the clinicopathological features of the case and the relevant literature about pelvic SFTs. In conclusion, SFTs should be considered in the differential diagnosis of any ischiorectal mass. It is recommended that tissue samples be obtained, and immunohistology should be performed.