An atypical case of a massive extra-articular pigmented villonodular synovitis

Pigmented villonodular synovitis (PVNS) is an idiopathic thickening of the synovium in form of nodules and villi. It commonly affects the knee. The synovium has fat and haem deposits. On MRI it appears heterogenous and its treatment is almost always a total synovectomy A 62-year-old female presented with a painless right knee swelling that was predominantly on the posterior aspect with some occasional mechanical symptoms of locking and catching with transient pain. MRI reported a large heterogenous hypointense mass that was 17.4cm by 9.0cm by 6.7cm. Biopsy confirmed PVNS and on surgery over and above the intra-articular component and a single large encapsulated posteriorly-located mass excised which was extra-articular. This particular case of a massive extra-articular PVNS is extremely rare and an important learning point while managing these cases with arthroscopy.