Intense PSMA-expression using 68Ga-PSMA PET/CT in a paravertebral schwannoma mimicking prostate cancer metastasis

Abstract

The prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer (PC) cells. The recently introduced PSMA-PET/CT has evolved as a powerful imaging tool for staging of PC [1–3]. Albeit the high specificity of PSMAtracers, there are reports of high PSMA-expression in nonprostatic malignant (e.g., renal cell carcinoma, bronchial carcinoma, and glioblastoma) and benign (schwannomas) lesions [4]. These reports raise concerns over the specificity of PSMA-PET imaging indicating the need for thorough review of accompanying morphological images besides exclusive interpretation of and reliance on PSMA-expression in PET. A 69-year-old patient with PC (Gleason 6 [3+3],iPSA 11.3 ng/ml) underwent Ga-PSMA-PET/CT for primary staging. Ga-PSMA-PET/CT showed intense PSMA-expression in the prostate representing the histological proven primary PC (A: MIP). Intense PSMA-expression was also observed in projection on a right paravertebral soft-tissue mass (B-D). Due to pain in the thoracic spine the patient had undergone MRI one month before. Images revealed typical features of a schwannoma showing a slightly hyperintense signal in T2w (E) and dumbbell configuration in coronal T2w stir with pathognomonic growth along the neuroforamen (F). In addition, T1w images showed a native hypointense lesion with inhomogeneous contrast enhancement (G,H). Thus, the patient was diagnosed with local PC without metastatic spread. This case advises caution particularly in patients with solitary Blesions^ as the interpretation of PSMA-PET/CT scans might directly influence therapy guidance (curative surgical vs. palliative medical treatment). In this case, typical MRI features (localization relative to the nerve, typical configuration) [5] as well as a former report of possible positive PSMAexpression in schwannomas [4] led to the diagnosis of this benign lesion.