Diagnosis of transition zone prostate cancer using T2-weighted (T2W) MRI: comparison of subjective features and quantitative shape analysis.

PURPOSE: To assess T2-weighted (T2W) MRI to differentiate transition zone (TZ) prostate cancer (PCa) from benign prostatic hyperplasia (BPH).

MATERIALS AND METHODS: With IRB approval, 22 consecutive TZ PCa were retrospectively compared with 30 consecutive BPH (15 stromal, 15 glandular) nodules diagnosed using radical prostatectomy MRI maps. Two blinded radiologists (R1/R2) subjectively assessed the shape (round/oval vs. lenticular) and margin (circumscribed vs. blurred/indistinct) and for a T2W hypointense rim. Both radiologists segmented lesions extracting quantitative shape features (circularity, convexity and topology/skeletal branching). Statistical tests were performed using chi-square (subjective features), Mann-Whitney U (quantitative features), Cohen's kappa/Bland-Altman and receiver-operator characteristic analysis.

RESULTS: There were differences in the subjective analysis of the shape, margin and absence of a T2W-rim comparing TZ PCa with BPH (p < 0.0001) with moderate to almost perfect agreement [kappa = 0.56 (shape), 0.72 (margin), 0.97 (T2W-rim)]. Area under the curve (AUC ± standard error) for diagnosis of TZ PCas was shape = 0.88 ± 0.05, margin = 0.89 ± 0.04, and T2W-rim = 0.91 ± 0.04. Shape, judged subjectively, was specific (100%/94% R1/R2) with low-to-moderate sensitivity (55%/88% R1/R2). Circularity and convexity differed between groups (p < 0.001) with no difference in topology/skeletal branches (p = 0.31). Agreement in measurements was substantial for significant quantitative variables and AUC ± SE, sensitivity and specificity for diagnosis of TZ PCa were: circularity = 0.98 ± 0.01, 90%/96%; convexity = 0.85 ± 0.06, 68%/97%. AUCs for circularity were higher than for subjective analysis (p = 0.01 and 0.26).

CONCLUSION: Subjective analysis of T2W-MRI accurately diagnoses TZ PCa with high accuracy also demonstrated for quantitative shape analysis, which may be useful for future radiogenomic analysis of transition zone tumors.

KEY POINTS: • Presence of a complete T2-weighted hypointense circumscribed rim accurately diagnoses BPH. • Round shape accurately diagnoses BPH and can be assessed quantitatively using circularity. • Lenticular shape accurately diagnoses TZ PCa and can be assessed quantitatively using convexity.