Elevated PSA with low ⁶⁸ Ga-PSMA and ¹⁸ F-FDG uptake in a periprostatic perineurioma

A 68-year-old male patient presented with a 4-month history of dysuria and an elevated prostate-specific antigen (PSA) level of 21.4 ng/mL. Contrast-enhanced CT revealed a purely extraprostatic 5-cm anterior periprostatic mass. 18 F-fluorodeoxyglucose ( 18 F-FDG) and 68 Ga-prostate-specific membrane antigen ( 68 Ga-PSMA)​ positron emission tomography/magnetic resonance imaging (PET/MRI) revealed low dual-tracer uptake (maximum standardized uptake value [SUV max ] = 2.4 for both tracers) with benign features, including neural tumor-specific T2 septations, preserved apparent diffusion coefficient (ADC), and type 2 plateau enhancement. Histopathological analysis confirmed the diagnosis of periprostatic perineurioma (epithelial membrane antigen [EMA]+/CD34+/S100-, Ki67 index 1%). This case highlights the value of multimodal PET/MRI for accurate characterization of pelvic tumors, particularly in distinguishing rare benign entities from malignancy.