Morphometric analysis of prostate zonal anatomy using magnetic resonance imaging: impact on age-related changes in patients in Japan and the USA.

OBJECTIVES: To evaluate the impact of morphometric magnetic resonance imaging (MRI) analysis of the prostate zonal anatomy on aging, prostatic hypertrophy and lower urinary tract symptoms in patients from Japan and the USA. SUBJECTS AND METHODS: A retrospective analysis of 307 men, including 156 men from Japan and 151 from the USA, who consecutively underwent 3-Tesla MRI and International Prostate Symptom Score (IPSS) assessment because of elevated PSA levels. Using Synapse-Vincent (Fujifilm), the prostatic zones were segmented in each axial step-section of the T2-weighted MRI to reconstruct a three-dimensional model of the prostate, which was used to calculate: zonal volumes (whole-gland prostate, transition zone and peripheral zone volumes); the presumed circle area ratio (PCAR); and PZ thickness. Bivariate associations were quantified using Spearman's rank correlation coefficients. RESULTS: The USA subgroup had a greater prostate volume (49 vs 42 mL; P = 0.003) and TZ volume (26 vs 20 mL; P < 0.001) than the Japan subgroup, with no difference in PZ volume (19 vs 20 mL; P = 0.2). There was no age-related increase in PZ volume in either of the subgroups or in the entire cohort (P = 0.9, P = 0.2, P = 0.3, respectively). PZ thickness had a significant negative correlation with PCAR (P < 0.001) and TZ volume (P < 0.001). The greater the increase in the TZ volume with the increase in PCAR, which probably correlates with obstructive pressure, the thinner the PZ became. PCAR had a significant positive correlation with IPSS (P = 0.003) and obstructive symptoms (P = 0.007), while PZ thickness had a significant negative correlation (P = 0.018). CONCLUSIONS: No age-related increases and no differences between the Japanese and the US subgroups were found with regard to PZ volume. The more TZ volume increased, the higher the obstructive pressure and the thinner the PZ became; these changes were associated with increased obstructive symptoms. MRI analysis of prostate zonal anatomy enhanced our understanding of age-related changes in morphology and urinary symptoms.