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

Abstract

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.

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