Recurrent diffuse tenosynovial giant cell tumor of the posterior knee: a rare presentation with synovial herniation (Baker's cyst) in a young patient.

Abstract

Introduction: Tenosynovial giant cell tumor (TGCT), previously referred to as pigmented villonodular synovitis (PVNS), is a rare, locally aggressive proliferative disorder of the synovium. It typically affects large joints, most commonly the knee. Posterior compartment involvement in the knee is less common compared to anterior or suprapatellar involvement, and it presents unique diagnostic and therapeutic challenges due to the complex anatomy and proximity to neurovascular structures. While popliteal (Baker's) cysts may coexist with intra-articular TGCT, they are considered synovial herniation cysts rather than true extra-articular involvement, which can be associated with diagnostic and therapeutic challenges.

Case presentation: This case report describes a 24-year-old male with recurrent diffuse TGCT of the knee, predominantly involving the posterior compartment, along with a large Baker's cyst and synovial thickening adjacent to the medial femoral condyle. Magnetic resonance imaging (MRI) revealed extensive synovial proliferation with characteristic low T2 signal intensity, confirming the diagnosis and guiding surgical planning. The patient underwent arthroscopic-assisted synovectomy to address both the suprapatellar and posterior compartments while preserving critical neurovascular structures. Postoperatively, the patient had improved knee function and was referred for adjuvant therapy to minimize recurrence risk.

Conclusion: This case highlights the importance of accurate imaging, meticulous surgical planning, and a multidisciplinary approach in managing rare presentations of TGCT. Long-term follow-up and consideration of adjuvant therapies such as radiotherapy or systemic therapies, including Pexidartinib, remain essential to minimize recurrence and optimize outcomes.