MRI features of the normal prostatic peripheral zone: the relationship between age and signal heterogeneity on T2WI, DWI, and DCE sequences

Abstract

Objectives: To assess the multiparametric MRI (mpMRI) appearances of normal peripheral zone (PZ) across age groups in a biopsy-naïve population, where prostate cancer (PCa) was subsequently excluded, and propose a scoring system for background PZ changes.

Methods: This retrospective study included 175 consecutive biopsy-naïve patients (40-74 years) referred with a suspicion of PCa, but with subsequent negative investigations. Patients were grouped by age into categories ≤ 54, 55-59, 60-64, and ≥ 65 years. MpMRI sequences (T2-weighted imaging [T2WI], diffusion-weighted imaging [DWI]/apparent diffusion coefficient [ADC], and dynamic contrast-enhanced imaging [DCE]) were independently evaluated by two uro-radiologists on a proposed 4-point grading scale for background change on each sequence, wherein score 1 mirrored PIRADS-1 change and score 4 represented diffuse background change. Peripheral zone T2WI signal intensity and ADC values were also analyzed for trends relating to age.

Results: There was a negative correlation between age and assigned background PZ scores for each mpMRI sequence: T2WI: r = - 0.52, DWI: r = - 0.49, DCE: r = - 0.45, p < 0.001. Patients aged ≤ 54 years had mean scores of 3.0 (T2WI), 2.7 (DWI), and 3.1 (DCE), whilst patients ≥ 65 years had significantly lower mean scores of 1.7, 1.4, and 1.9, respectively. There was moderate inter-reader agreement for all scores (range κ = 0.43-0.58). Statistically significant positive correlations were found for age versus normalized T2WI signal intensity (r = 0.2, p = 0.009) and age versus ADC values (r = 0.33, p = 0.001).

Conclusion: The normal PZ in younger patients (≤ 54 years) demonstrates significantly lower T2WI signal intensity, lower ADC values, and diffuse enhancement on DCE, which may hinder diagnostic interpretation in these patients. The proposed standardized PZ background scoring system may help convey the potential for diagnostic uncertainty to clinicians.

Key points: • Significant, positive correlations were found between increasing age and higher normalized T2-weighted signal intensity and mean ADC values of the prostatic peripheral zone. • Younger men exhibit lower T2-weighted imaging signal intensity, lower ADC values, and diffuse enhancement on dynamic contrast-enhanced imaging, which may hinder MRI interpretation. • A scoring system is proposed which aims towards a standardized assessment of the normal background PZ. This may help convey the potential for diagnostic uncertainty to clinicians.

Keywords: Aging; Anatomy; Multiparametric MRI; Normal anatomy; Prostate cancer.

Fig. 1

Image examples of T2-weighted imaging scores 1 to 4. Detailed descriptors can be found in Table 1

Fig. 2

A 44-year-old man with a family history of prostate cancer, PSA 0.5 ng/mL and subsequent negative transrectal-ultrasound-guided biopsy. T2-weighted (a), early-phase dynamic contrast-enhanced (b), b-2000 diffusion-weighted (c), and apparent diffusion coefficient map (d) images show features of score 4 for each of the individual sequences

Fig. 3

Relationships between (a) age and whole gland (WG) volume and (b) age and transition zone (TZ) volume, on MRI (n = 174, 1 outlier excluded). The graphs show that both WG and TZ volumes increase with increasing age

Fig. 4

T2-weighted imaging (T2WI) score distribution among the four age groups (≤ 54, 55–59, 60–64, and ≥ 65 years); scores reduce with increasing age

Fig. 5

Relationship between age and T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI) scores. Scores reduce as age increases

Fig. 6

Relationship between age and peripheral zone (PZ) normalized T2-weighted imaging (T2WI) signal intensity. The graph shows T2WI signal intensity increases with increasing age