Prostatic Ductal Adenocarcinoma: an Aggressive Tumour Variant Unrecognized on T2 Weighted Magnetic Resonance Imaging (MRI)

Introduction: Prostatic ductal adenocarcinoma (DCa) is an aggressive variant. The purpose of this study was to determine if T2 signal intensity (SI) differs from conventional adenocarcinoma (CCa).

Materials And Methods: A retrospective study of patients who underwent preoperative MRI and prostatectomy between 2009 and 2012 was performed. T2 SI ratios (SIR) for tumour (T) to obturator internus muscle (M) and normal peripheral zone (PZ) were compared. Two radiologists evaluated the central gland/PZ to detect tumours and compared diagnostic accuracy.

Results: T2 SIR for DCa were 3.60 (T/M), 0.66 (T/PZ); 2.68 (T/M), 0.47 (T/PZ) for Gleason 9; 2.50 (T/M), 0.47 (T/PZ) for Gleason 7/8 and 3.95 (T/M), 0.73 (T/PZ) for Gleason 6 tumours. There was a difference in T2 T/M and T/PZ SIR between DCa and Gleason 9 (p = 0.003, p = 0.004) and Gleason 7/8 (p = 0.006, p = 0.002), but no difference in SIR between DCa and Gleason 6 tumours. The sensitivity for tumour detection was 0-27 % for DCa, 64-82 % for Gleason 9, 44-88 % for Gleason 7-8 and 0-20 % for Gleason 6. There was a difference in the sensitivity of detecting Gleason 9 and 7/8 tumours when compared to DCa (p = 0.004, p = 0.001).

Conclusions: DCa resembles Gleason score 6 tumour at T2-weighted MRI, which underestimates tumour grade and renders the tumour occult.

Key Points: Prostatic ductal adenocarcinoma is aggressive, resembling endometrial carcinoma at histopathology. Prostatic ductal adenocarcinoma resembles Gleason score 6 tumour at T2-weighted MRI. MRI grading may underestimate ductal adenocarcinoma based on increased T2 signal.