Prediction of extraprostatic extension on multi-parametric magnetic resonance imaging in patients with anterior prostate cancer

Abstract

Objectives: To validate how established markers of extraprostatic extension (EPE) are applied to anterior prostate cancers (APCs), and to investigate other novel markers if available.

Methods: Among 614 histopathologically confirmed APCs from 2011 to 2016, 221 lesions with PiRADS (verion 2) scores ≥ 4 on 3-T multi-parametric MRI were analyzed retrospectively. Two radiologists independently assessed capsular morphology qualitatively with 5-point scale (normal, thinning, bulging, loss, extracapsular disease), and capsule contact length (arc), tumor dimension, and their ratio (arc-dimension ratio) quantitatively. Reproducibility in measurement was assessed with κ and intra-class correlation coefficients (ICCs). Logistic regression analysis was done to find meaningful indicators of EPE. Diagnostic performance of markers was compared to one another with generalized linear model and multi-reader multi-case ROC analysis.

Results: Reproducibility was moderate to substantial (κ 0.45-0.73) for qualitative, and moderate to almost perfect (ICC 0.50-0.87) for quantitative features of EPE. Capsular morphology (odds ratio [OR] 1.818), capsule contact length (OR 1.115), tumor dimension (OR 1.035), and arc-dimension ratio (OR 1.846) were independently associated with EPE (p ≤ 0.019). Capsular bulging and capsule contact length of 10 mm as thresholds of EPE demonstrated sensitivity/specificity of 0.58/0.85 and 0.77/0.68, respectively. Capsule contact length yielded greatest AUC (0.784), followed by capsular morphology (0.778), arc-dimension ratio (0.749), and tumor dimension (0.741). Diagnostic performance of capsular morphology, capsule contact length, and arc-dimension ratio was comparable in predicting EPE.

Conclusions: Existing markers of EPE applicable regardless of locations of tumors apply similarly to APCs. Arc-dimension ratio may be a novel marker of EPE of APCs.

Key points: • Existing imaging markers of extraprostatic extension (EPE) which have been applied regardless of locations of tumors are reflected similarly to anterior prostate cancers (APCs). • Measuring tumor dimension without capsular assessment may result in insufficient pre-operative prediction of EPE of APCs. • Arc-dimension ratio (capsule contact length divided by tumor dimension) exhibited highest OR and comparable performance to existing features in predicting EPE of APCs.

Keywords: Adenocarcinoma; Magnetic resonance imaging; Neoplasm staging; Prostatic neoplasms.