MRI pathway for small volume prostate gland index lesions: a single-centre retrospective analysis

By using MRI-guided in-bore biopsy, we examined the specific question of the significance of small volume index lesions that are increasingly prevalent in daily practice.

We retrospectively reviewed 602 consecutive men who underwent multiparametric MRI (mpMRI) and subsequent MRI-guided in-bore prostate biopsy between January 2010 and February 2025. One hundred seven patients with peripheral zone (PZ) small volume PI-RADS 4 index lesions (≤7 mm in greatest dimension) comprised the study cohort. Patient age, prostate-specific antigen (PSA) level, PSA density, target size, shape (round/oval, linear/wedge, or subcapsular crescentic), International Society of Urological Pathology (ISUP) Grade Group, and tumour length to core length ratio were correlated.

In this cohort, the mean age, PSA, prostate volume, PSA density, and lesion size were 63.8 years (range: 45-79 years), 5.6 ng/mL (range: 1.6-18 ng/mL), 53.5 mL (range: 14-151 mL), 0.12 ng/mL2 (range: 0.02-0.43 ng/mL2) and 5.7 mm (range: 3-7 mm), respectively. A total of 107 patients were examined, of whom 71 (66.3%) were found to have prostate cancer (PCa) and 47 (43.9%) had clinically significant prostate cancer (csPCa). The percentage of linear/wedge-shaped targets was 50.5% (n = 54/107) and the detection rates of PCa and csPCa for this subgroup were 61.1% (n = 33/54) and 48.1% (n = 26/54), respectively.

Our study reveals that a higher percentage of small volume index lesions harbour a high grade (Gleason pattern 4 or 5) component than previously thought, suggesting that lesion size alone does not provide sufficient reassurance to omit biopsy. MRI-guided in-bore biopsy is a valuable technique for accurately sampling and characterizing small-volume index lesions.

Nearly half of the small volume index lesions on mpMRI are clinically significant regardless of their shape and these lesions cannot be safely ignored.