False positive MRI prostate: focal prostatitis
Previous T1C Gleason 3+3 = 6 prostate cancer on active surveillance. Slight increase in PSA. MRI to determine extent of tumour infiltration
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Large area of diffuse T2 hypointensity in the peripheral zone of right base and mid prostate. Restricted diffusion on DWI and the ADC map with increased early enhancement following bolus IV Gad injection. No capsular breach. Right lobe is perhaps a little smaller than the left. This indicates at least a PIRADS 4 lesion requiring biopsy for confirmation of neoplasm.
MRI prostate is useful at detecting and locally staging prostate cancer but there are false positives. Features of cancer are T2 hypointensity with restrictted diffusion and early, rapid washout enhancement as in this case. Transperineal template biopsy (with fused US guidance targetting the right sided MRI findings) in this case showed "patchy mixed inflammatory cell infiltrate" but no malignancy in all right sided biopsies and only "moderate acinar atrophy" in the left side. No malignancy detected. This patient therefore has focal right-sided (asymptomatic) prostatitis causing a false positive for malignancy on MRI and increase in PSA.