Late Renal Cell Carcinoma Metastasis Mimicking an Arteriovenous Malformation in the Parotid and Masseter Region: A Diagnostic Pitfall

Renal cell carcinoma (RCC) is characterized by unpredictable metastatic behavior and the potential for recurrence many years after initial treatment. Metastases to the head and neck region are uncommon, and involvement of the masseter muscle is exceptionally rare, often creating a diagnostic challenge. We report the case of a 77-year-old man with a history of radical nephrectomy for RCC 12 years earlier who presented with a painless, progressively enlarging mass in the right parotid region. Imaging studies demonstrated a markedly hypervascular lesion with high-flow characteristics, initially suggestive of an arteriovenous malformation. However, the patient’s oncologic history prompted further investigation, and ultrasound-guided fine-needle aspiration confirmed metastatic clear cell RCC. He underwent superficial parotidectomy with en bloc resection of the masseteric lesion. Histopathologic examination and immunohistochemical staining demonstrating focal PAX8 positivity and diffuse carbonic anhydrase IX (CAIX) expression confirmed the diagnosis. This case highlights the ability of late RCC metastases to mimic vascular lesions because of their marked hypervascularity, particularly in unusual anatomical locations. Metastatic RCC should remain in the differential diagnosis of hypervascular head and neck masses, even after prolonged disease-free intervals.