Prostatic remnant after prostatectomy: MR findings and prevalence in clinical practice

OBJECTIVE. The purpose of this article is to evaluate the MR findings of prostatic remnant after prostatectomy and estimate the prevalence of prostatic remnant in patients that undergo MRI after prostatectomy. MATERIALS AND METHODS. Sixty-six patients who had undergone radical prostatectomy with pathologically proven benign prostatic remnant between 2007 and 2017 were retrospectively reviewed. Pathologically proven benign prostatic remnant was determined on the basis of initial pathologic report. Of the 66 initial patients, 30 patients with biopsy-proven benign prostatic remnant without coexisting recurrent prostate carcinoma and three patients who underwent repeat resection for completion prostatectomy were enrolled. MRI characteristics including location, size, signal intensity on T2-weighted images and DWI, and contrast enhancement pattern were analyzed. Nine additional patients were found to have a prostatic remnant by imaging without biopsy. The prevalence of prostatic remnant among those undergoing MRI for suspected recurrence during the same period was estimated. RESULTS. Prostatic remnant was detected in 23 of 33 patients on MRI. The remaining 10 patients did not have any visible abnormality. The 23 detected lesions were located in three regions: under the vesicourethral anastomosis in five patients, in the bladder neck in 12 patients, and posterior to the bladder in six patients. On T2-weighted imaging, 17 of 23 lesions showed heterogeneous hyperintensity. On DWI, 14 lesions showed hyperintensity. Dedicated MRI studies were performed for suspected prostate cancer recurrence in 2466 patients during the same period. Prevalence of exclusively benign prostate remnant detectable on MRI was approximately 1% of that population (23/2466-35/2466), and overall prevalence of any prostate remnant detectable on MRI was 3% (75/2466). CONCLUSION. Benign prostate remnant after prostatectomy occurs at three common sites and typically shows heterogeneous hyperintensity on T2-weighted imaging. The prevalence of detectable prostatic remnant in men who undergo MRI for suspected recurrence was approximately 1-3%.