Quantification and significance of extraprostatic findings on prostate MRI: a retrospective analysis and three-tier classification

Abstract

Objectives: To quantify extraprostatic findings (EPFs) on prostate MRI, estimate the proportion of reported and unreported EPFs, assess their clinical importance, and propose standardized reporting of EPFs.

Materials and methods: Prostate 3-T MRI studies, reports, and clinical data from 623 patients (age 67.9 ± 8.2 years) were retrospectively analyzed and re-evaluated for the presence of EPFs and their clinical significance: E1-no finding or findings that have no clinical significance; E2-potentially significant findings; and E3-significant findings.

Results: Secondary reading identified 1236 EPFs in 593 patients (1.98 ± 1.13 EPFs per patient, no EPFs in 30 patients), from which 468 (37.8%) were mentioned in the original report. The most common findings included diverticulosis (44% of patients), hydrocele (34%), inguinal fat hernia (16%), and bladder wall trabecular hypertrophy (15%). There were 80 (6.5%) E2 EPFs and 30 (2.4%) E3 EPFs. From E3 EPFs, 10 (33%) were not originally reported. A workup was suggested in 35 (52%) of the 67 originally reported E2 and E3 findings with follow-up and performed in 20 (30%). Fourteen (21%) EPFs in 11 patients influenced their management. Four experienced radiologists originally reported 1.8 to 2.5 findings per patient (p < 0.0001).

Conclusions: EPFs on prostate MRI are frequent, but only 2.4% are clinically significant (E3), and 33% of these are not reported. Only 30% of E2 and E3 findings are further explored, and 21% influence patient management. We suggest that an "E" category should be attached to the PI-RADS system to identify the presence of EPFs that require further workup.

Critical relevance statement: Extraprostatic findings on prostate MRI are frequent, but only 2.4% are clinically significant (E3), and 33% of these are not reported. We advocate standardized reporting of extraprostatic findings indicating their clinical significance.

Key points: • Extraprostatic findings on prostate MRI are frequent with an average of two findings per patient. • 2.4% of extraprostatic findings are significant, and 33% of these are not reported. • There is a significant variability among experienced radiologists in reporting extraprostatic findings.

Keywords: Cancer; Extraprostatic findings; Magnetic resonance imaging; PI-RADS; Prostate.

Fig. 1

Study flowchart

Fig. 2

Number of extraprostatic findings per patient (a). Number of reported and unreported findings according to their significance (b). Number of findings per patient according to age stratified by their significance (c). Number of extraprostatic findings according to the imaging protocol (P1, P2, and P3; d). P2 denotes protocol with limited anatomical coverage

Fig. 3

Examples of significant findings that were not included in the original report (T2-weighted fast spin echo). Diffuse bone marrow changes (a). Bladder wall tumor (b). Perianal fistula (c). Lymphadenopathy (d). Hydroureter (e). Sigmoid cancer (f)