Pigmented Villonodular Synovitis: A Metastatic Melanoma Imitator

Area of Science:

• Oncology
• Pathology
• Radiology

Background:

• Melanoma metastasis can present as diverse clinical and imaging findings.
• Accurate differentiation of metastatic lesions from benign mimics is crucial for patient management.

Observation:

• A patient with a history of melanoma developed a thigh mass and knee nodule.
• Imaging revealed PET-avidity and MRI enhancement in both lesions, suspicious for metastatic melanoma.
• Histopathological analysis of the knee nodule showed features mimicking metastatic melanoma.

Findings:

• The thigh mass was confirmed as metastatic melanoma.
• The knee nodule, initially suspected as melanoma metastasis, was ultimately diagnosed as pigmented villonodular synovitis.
• Immunohistochemical studies were essential in excluding melanoma cells in the knee lesion.

Implications:

• This case underscores the importance of considering benign mimics in the differential diagnosis of suspected melanoma metastasis.
• Pathological correlation, including immunohistochemistry, is vital for accurate diagnosis and appropriate treatment planning.
• Awareness of pigmented villonodular synovitis as a potential mimic can prevent misdiagnosis and guide further investigation.