The overall results of this study are similar to those of previous studies. The sensitivity of all lesions with a PI-RADS score of ≥ 3 was 61.4% in this study and 31–62% in previous studies that used RP specimens (Table 3)[6, 10, 15, 20]. The low sensitivity of all lesions reflects the low sensitivity of small and low-GS lesions. However, even in GS ≥ 8, mpMRI misdiagnosed one-third of the lesions with diameters of ≤ 10 mm. In lesions with GS 3 + 4 and diameter ≤ 10 mm, the sensitivity was only 31.6%, which caused the low sensitivity of csCaP/GS ≥ 3 + 4 (77.7%) (Table 3). Detection rates for csCaP/GS ≥ 3 + 4 (67–75%) in previous studies were similar.
csCaP is usually defined as lesions with GS ≥ 3 + 4 or diameter > 10 mm. However, National Comprehensive Cancer Network guidelines also recommend active surveillance for GS 3 + 4 lesions. In addition, some recent studies have defined GS ≥ 4 + 3 as csCaP. Therefore, we used two types in the analysis of csCaP. Compared with csCaP/GS ≥ 3 + 4, the sensitivity of csCaP/GS ≥ 4 + 3 in this study (85.7%) and in previous studies (91–95%) was relatively high  (Table 3).
It has been suggested in recent reports that lesions associated with cancer progression and metastasis could be the largest lesions in prostate or highest GS within 5 mm of maximum, called IT . Focal therapy for limited CaP is rationally based on IT hypothesis. Multiparametric MRI, which might be considered a suitable tool for IT detection, has a high detection rate for IT (91% in this study and 80–91% in the previous studies). Nevertheless, the approximately 10% rate of misdiagnosis needs our attention (Table 3).
Tumors undetected in mpMRI are often characterized as small and multifocal. Ninety-one (39.9%) lesions in this study were mpMRI negative, 67 (73.6%) of which were insignificant cancers (GS ≤ 3 + 4 and ≤ 10 mm) (Table 4). In case of IT, most undiagnosed lesions were multifocal cancers. However, it was surprising that two cases had an IT with ≥ 20 mm and GS 4 + 5. A previous study using mainly 3 T mpMRI mentioned that mpMRI negative lesions could be high GS, but large lesions with a high GS were fully detectable. The intensity of the applied magnetic field may be reason for the missing cases with high-grade and large lesions in our study. In a study by Ulrich et al., the correlation between 1.5 and 3 T within the same patients was reported. This study revealed that comparable objective image quality is revealed by 1.5 T MRI in T2WI but is inferior to 3 T in DWI. The conclusions of the study indicated feasible diagnostic performance even in 1.5 T MRI. However, the inferiority of 1.5 T MRI in DWI might lead to the misdiagnoses in this study.
Positive SM is an important factor that reflects the postoperative outcome . Postoperative functional outcomes, including continence and erectile function, are improved by neurovascular bundle preservation techniques , which potentially increase positive SM when neurovascular bundle is preserved on the EPE positive side. Although mpMRI is mainly used to predict EPE before surgery, previous reports have mentioned that the sensitivity of EPE is not enough. A meta-analysis showed a sensitivity of 57% and a specificity of 91% for microscopic EPE. The sensitivity and specificity in this study were only 11.8% and 100%, respectively (Table 6). Positive mpMRI lesions had more positive EPE and SM than mpMRI negative lesions (Table 3).
Several limitations of this study should be mentioned. First, this was a retrospective study. Second, the PI-RADS score was estimated by a single physician. Several studies have revealed that there are diagnostic differences across readers[10, 30]. Third, there could be differences in characteristics between patients who underwent RP in this study and those who underwent other treatments. Fourth, up to three lesions were always evaluated; however, minimal lesions beyond these three were excluded from this analysis.