Prostate MRI followed by trans-gluteal CT-guided biopsy

Clinical History

Benign prostatic hypertrophy. Rising PSA, now >12 ng/mL, urinary obstruction. Previous colectomy for ulcerative colitis. No rectum currently.

Imaging Findings

Prior to contrast administration, general survey of the prostate gland demonstrates heterogeneity and cystic change with rounded nodules in the central zone of the gland. No worrisome mass in the peripheral zone is identified. The seminal vesicles are somewhat prolific and extend fairly cephalad above the gland; however, there is no infiltrative mass seen. No pelvic sidewall lymph nodes of significant size. The urinary bladder is grossly normal. There is paramagnetic artifact from prior colon and rectal resection at the deep posterior pelvis.

After dynamic contrast enhancement of the gland, it is difficult to identify a discrete enhancing nodular mass. There is very low enhancement surrounding what is likely an adenoma in the central left paramedian aspect of the gland. No other abnormal enhancement in the field-of-view is seen. Diffusion images to include b=1000 images and ADC maps grossly do not appear abnormal.

Discussion

Background: The data set was sent for review with computer aided detection (DynaCAD, Invivo Corp., Pewaukee, WI). Upon review of the data, there is a focus of gland abnormality in the left, more cephalad half of the gland at the margin of the central zone, Fig. 1 on ADC map images and Fig. 2 on the SPGR contrast enhanced images, where in retrospect there does appear to be a degree of asymmetric enhancement at this portion of the left paramedian gland. The T2-weighted axial also demonstrates an area of low signal intensity in the lateral horn of the peripheral zone(Fig. 3). This is considered suspicious for a possible primary site of prostate carcinoma. Scrolling through the entire dataset the enhancement pattern is bilateral and symmetric, so not as much of a concern as the unilateral focus. No other focal suspicious abnormalities are seen. Based on MRI findings, trans-gluteal, CT-guided biopsy was performed the following month (Fig. 4). Of the six cores acquired, four contained Gleason 7 (3+4) prostate carcinoma. Approximately 60% of the positive cores were carcinoma. Perineural invasion was not identified.

Clinical Perspective: CAD can assist in the identification of tumor suspicious regions in the prostate gland and aid in biopsy guidance.

Imaging Perspective: As MRI has improved over the past two decades for prostate imaging, it has proven to be a valuable tool when inserted appropriately in the diagnostic evaluation of patients with elevated PSA.

Outcome: This patient had a history of BPH when in fact he was harboring prostate cancer.

Take Home Message, Teaching Points: Properly performed, multi-parametric MRI consisting of T2-weighted images in all three planes, DWI with ADC maps and dynamic contrast enhanced imaging can solve diagnostic dilemmas in patients with elevated PSA [1]. Targeted, MRI-guided biopsy performed with a trans-glueteal, CT-guided approach is practical in patients with no rectum.

Differential Diagnosis List

Final Diagnosis

Prostate carcinoma, Gleason 7 (3+4)

URL:	https://eurorad.org/case/10233
DOI:	10.1594/EURORAD/CASE.10233
ISSN:	1563-4086