Pitfalls in Gallium-68 PSMA PET/CT Interpretation-A Pictorial Review

The novel Gallium-68 prostate-specific membrane antigen (PSMA)-bis [2-hydroxy-5-(carboxyethyl)benzyl] ethylenediamine-diacetic acid positron emission tomography (PET) tracer is increasingly used in the evaluation of prostate cancer, particularly in the detection of recurrent disease. However, PSMA is expressed in nonprostatic tissues, as well as in other pathologic conditions. Here we illustrate such interpretive pitfalls with relevant images that one may encounter while reporting PSMA PET/CT. This study aims to show variation in physiological distribution of PSMA activity and uptake in various benign and neoplastic disorders that may be misinterpreted as prostatic metastatic disease. These pitfalls are illustrated to enhance awareness, aiding a more accurate interpretation of the study. Retrospective database of all (68)Ga PSMA PET/CT was created and reviewed. In total, 1115 PSMA PET/CT studies performed between February 27, 2015, and May 31, 2017, were reviewed. Any unusual uptake of PSMA was documented, described, and followed up. All cases were then subdivided into the following 4 categories: physiological uptake, benign pathological uptake, nonprostatic neoplastic uptake, and miscellaneous uptake. A variety of nonprostatic tissues and lesions, including accessory salivary gland, celiac ganglion, gall bladder, Paget's bone disease, reactive lymph nodes, non-small cell lung cancer, renal cell cancer, and neuroendocrine tumor, were found to show PSMA uptake. PSMA uptake is not prostate-specific and can be taken up physiologically and pathologically in nonprostatic tissue. It is important for reporting physicians to recognize these findings and instigate appropriate investigations when required while avoiding unnecessary procedures in physiological variation.