Fibroma of tendon sheath on the medial side of the knee: a case report.

Fibroma of tendon sheath, which is a benign soft tissue tumor, primarily affects the finger, hand, or wrist. It rarely involves the knee and only a few cases appear in the literature. Here, we report a case of fibroma of tendon sheath on the medial side of the knee, in a previously hardly reported location, and provide detailed imaging and histological findings. A 54-year-old man presented with his right knee pain and a palpable mass that had developed 3 months earlier. Magnetic resonance imaging showed isointensity in the soft tissue tumor on T1-weighted images, variable intensity on T2-weighted images, and contrast enhancement. The specimen obtained by needle biopsy showed no histological findings of malignancy. Marginal resection was performed and the microscopic diagnosis was fibroma of tendon sheath. Since fibroma of tendon sheath is relatively rare, the radiological feature is not specific, and a rate of local recurrence following excision is high, careful diagnosis, surgical treatment and long-term follow-up are necessary. J. Med. Invest. 64: 173-176, February, 2017.