Fibroma of the tendon sheath around the knee

Fibroma of tendon sheath is an uncommon benign soft tissue tumor, intimately associated with tendons or tendon sheaths, with a predilection for the upper extremity. Fibroma of the tendon sheath around the knee is extremely rare. We report a case of a 51-year-old man who presented a tumor involving the posteromedial aspect of the left knee and which progressed in size for 7 years. Magnetic resonance imaging demonstrated a heterogeneous high-signal intensity in the mass on T1 and T2-weighted images. The tumor was excised en bloc. Macroscopically, it was lobulated and measured 13 cm in its largest diameter. Histology led to the diagnosis of fibroma of the tendon sheath. At 6 years’ follow-up, there was no local recurrence. To the best of our knowledge, the location and the size of this fibroma of the tendon sheath have never been described.