False-positive mpMRI and true-negative ⁶⁸Ga-PSMA PET/CT xanthogranulomatous prostatitis: a case report

Xanthogranulomatous prostatitis (XGP) is a rare disorder of the prostate. It presents as a hard fixed nodule on digital rectal examination (DRE), and may cause obstructive urinary symptoms and elevated serum prostate-specific antigen (PSA) levels, therefore mimicking prostate cancer (PCa) clinically and biochemically. Radiological features of XGP overlap with those of PCa, and the 2 conditions cannot be distinguished by pelvic multiparametric magnetic resonance imaging (mpMRI). ⁶⁸Ga-labelled prostate-specific membrane antigen (⁶⁸Ga-PSMA) with positron emission tomography/computed tomography (PET/CT) has shown its potential in the initial diagnosis and staging of PCa; however, the imaging characteristics of XGP on ⁶⁸Ga-PSMA PET/CT have yet to be reported.

We report the case of a 56-year-old man who had slowly progressing dysuria for 10 years, which was significantly worse for 1 week, and a PSA level of 49.19 ng/L. Ultrasound revealed a hypoechoic lesion in the left periphery of the prostate, which was hypointense with capsular irregularity on axial T2-weighted imaging (T2WI), hyperintense on the diffusion weighted imaging (DWI), and hypointense on the apparent diffusion coefficient (ADC) maps resulting in a Prostate Imaging-Reporting and Data System (PI-RADS) score of 5. The patient was highly suspected of having high-risk PCa and underwent a ⁶⁸Ga-PSMA PET/CT for staging. The PET/CT images showed no PSMA uptake in the involved region. Considering that a small proportion of cases of PCa do not express PSMA, a subsequent targeted biopsy was performed, guided by mpMRI. Histopathological examination showed a large number of foamy macrophages in the neutrophile granulocyte infiltrate, and XGP was finally diagnosed. After treatment with antibiotic levofloxacin, the patient's PSA returned to normal, and his dysuria symptoms had disappeared at the 2-month follow-up.

Non-uptake of PSMA in a lesion may still provide information for a diagnosis by exclusion or regular follow-up checks in patients that are highly suspected to have PCa in clinic or on mpMRI.