Focal therapy for localised prostate cancer is becoming increasingly accepted as a viable treatment option due to its benefits in preserving functional outcomes for patients. In our centre, we utilise irreversible electroporation as our energy source of choice for focal therapy. However, follow up can be challenging as traditional MRI imaging can be difficult to interpret due to scarring and retraction of the prostate in the treated area. This case series demonstrates a number of false positive PSMA PET/CTs due to retraction of the prostate and formation of a pseudodiverticulum which contains urine and therefore mimics a positive PSMA with strong tracer activity in the urine.

A retrospective review was carried out of 376 patients who underwent primary IRE for prostate cancer in the period from February 2013 to February 2025. 7 patients were identified who had a positive focal lesion on PSMA PET/CT, but a subsequent negative biopsy.

Imaging for 7 patients are being presented here, with their pre-op MRIs, as well as their post op PET and MRI. The images demonstrate a bright focal lesion on PSMA PET which appears to be a strongly avid recurrence, however when compared to the T2 weighted MRI, a fluid filled cavity is clearly visible.

PSMA PET/CT interpretation can be challenging in the post IRE setting due to the presence of urine containing pseudodiverticulum. Given that the nuclear medicine physicians reviewing the PET may not have the MRI available to compare, or may not be dual trained radiologists, it is crucial that they are aware of these false positives caused by pseudodiverticulum following IRE focal therapy.