Why Uptake Matters? – A Case of the Second Primary in a Benign-Looking Renal Cyst of a Patient Undergoing 18f-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography for Treated Head-And-Neck Cancer

A 60-year-old male, a diagnosed case of squamous cell carcinoma of the hypopharynx, underwent 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) for response assessment. PET/CT revealed mildly increased 18F-FDG uptake and contrast enhancement in the region of the primary, which was suggestive of postradiation changes. Interestingly, a benign-looking cyst was seen in the shrunken, poorly-functioning left kidney, with mildly elevated 18F-FDG uptake. Structurally, the lesion appeared benign on ultrasound and sequential CT images. However, 18F-FDG was the only feature which alluded to the possibility of another pathology like low-grade malignancy or oncocytoma. The lesion was biopsied, which revealed Clear-Cell International Society of Urologic Pathologists grade-1 renal cell carcinoma. Consequently, the patient was posted for surgery.