Perianal Solitary Fibrous Tumor in a Rare Anatomical Presentation: A Case Report and Literature Review.

BACKGROUND Solitary fibrous tumors (SFTs) account for <2% of all soft tissue tumors and are slow-growing neoplasms of mesenchymal origin, which have been reported in various locations. They are frequently observed at the pleura and a perianal location is extremely rare. They show no predisposition by sex, are mainly benign, and usually occur between the 5th and 7th decades of life. CASE REPORT We report the case of an 80-year-old man with no comorbidities except hypertension, who presented with an asymptomatic perineal mass. Magnetic resonance imaging showed a solid tumor measuring 3.5×2.5 cm identified in the perineal midline. It was very close to the anal sphincter, showing no extension to the rectum or anus. The tumor was completely excised with negative margins. The postoperative course was uneventful and he was discharged home, free of any symptoms. The pathological examination showed a benign completely excised SFT, and no further treatment was necessary. At the 6-month and 1-year follow-ups, there was no sign of recurrence. CONCLUSIONS A comprehensive review of all the reported cases of perianal SFTs shows that the majority of these tumors present with no symptoms and have a favorable prognosis. Diagnosis is possible only after a pathological examination. The criterion standard of treatment is complete excision with negative margins. Once excised, the tumors have low rates of recurrence and metastasis. Tumors very close to the anal sphincter and with malignant potential need to be operated on with extra care to obtain clear margins without disrupting the continence mechanism.