PSMA-Avid, FDG-Non-Avid Testicular Lesion in Metastatic Castration-Resistant Prostate Cancer: A Presumed Rare Testicular Metastasis

Testicular metastasis from prostate carcinoma is exceedingly rare and generally indicates advanced disease with a poor prognosis. We report the case of a 61-year-old man with metastatic prostate carcinoma who developed progressive disease despite chemotherapy, androgen deprivation therapy, and androgen receptor pathway inhibitor therapy. Dual-tracer imaging with ⁶⁸ Ga prostate-specific membrane antigen (PSMA)-11 positron emission tomography/computed tomography (PET/CT) and ¹⁸ F Fluorodeoxyglucose (FDG) PET/CT was performed before planned lutetium ¹⁷⁷ PSMA radioligand therapy ( ¹⁷⁷ Lu- PSMA RLT). [ ⁶⁸ Ga]Ga-PSMA PET/CT demonstrated tracer-avid lesions in the prostate, bone, lymph nodes, and right testis, whereas the testicular lesion was non-avid on ¹⁸ F-FDG PET/CT, demonstrating a discordant uptake pattern similar to that of other metastatic sites. Clinical examination revealed a firm, painless right scrotal mass. Based on the serial imaging findings and clinical context, testicular metastasis was diagnosed without biopsy. This case highlights the value of combined [ ⁶⁸ Ga]Ga-PSMA and ¹⁸ F-FDG PET/CT in detecting and characterising rare metastatic sites noninvasively with increased diagnostic confidence.