Pigmented villonodular synovitis presenting as a subcutaneous mass at the knee

Area of Science:

• Orthopedic Surgery
• Pathology
• Radiology

Background:

• Pigmented villonodular synovitis (PVNS) is a rare, benign neoplastic proliferation of the synovium.
• Typically, PVNS affects large joints like the knee, hip, and ankle.
• It most commonly presents as an intra-articular mass, but extra-articular and subcutaneous presentations are documented.

Observation:

• A 45-year-old male presented with a painful subcutaneous mass near his knee.
• Magnetic resonance imaging (MRI) revealed a well-defined lesion.
• The clinical presentation mimicked a more common soft tissue tumor.

Findings:

• Biopsy confirmed the diagnosis of pigmented villonodular synovitis.
• Histopathological examination showed characteristic features of PVNS.
• The lesion was identified as a primary synovial process manifesting superficially.

Implications:

• This case underscores the importance of considering rare diagnoses in the differential for subcutaneous masses.
• Increased awareness of PVNS presenting as a subcutaneous tumor can aid in timely diagnosis and appropriate management.
• Radiological and pathological correlation is crucial for differentiating PVNS from other neoplastic and non-neoplastic conditions.