DISCUSSION
In this study, the correlation of prostate gland diseases with patient
age, gland volume, serum PSA value and, PSA density, the effectiveness
of the MpMRI and PI-RADSv2.1 scoring system in detecting prostate gland
diseases, PI-RADSv2.1 and ISUP score correlation, and interobserver
agreement were assessed. In our study, serum PSA did not show a
significant difference for malignant or benign disease. PSAd was
observed significantly high in the malignant group. Joshua Stephen Jueve
et al. reported a sensitivity of 90-95% for PSAd and considering the
0.15 ng/ml2 threshold value, they supported that the
high NPV may prevent unnecessary biopsy in patients with proportional
PSA increase compared to prostate volume11. There was
a negative correlation found between prostate volume and malignancy
diagnosis. This result is similar to the results of studies by Shadi
Al-Khalil et al.12 and Tang et
al.13. The causes for the increase of prostate volume
may be interpreted as due to benign causes like hyperplasia and
prostatitis. The study of Haas et al. presented that patients with
prostate cancer were of advanced ages14. Droz et al.
showed high mean age in the cancer group15. In our
study, the mean age in the cancer group was consistent with the
literature and was higher compared to benign diseases of the prostate
gland; however, the difference was not statistically
significant(p:0.053). PI-RADSv2 is a scoring system widely used for the
detection of PCa and its reliability has been demonstrated by numerous
studies. When we examine these studies in the literature, the cut-off
value for detection of clinically significant prostate cancer on MpMRI
of PI-RADS 3 or 4 had ranges of 85.7-94.5% for sensitivity, 23-71% for
specificity, and 34-97% and 50-92% for PPV and NPV,
respectively16–21. Venderink et
al.22 determined the clinically significant PCa rates
(GS≥3+4) for PI-RADS-3, 4, and 5 lesions were 17%, 34%, and 67%,
respectively. A study by Mathur et al. found the detection rates for
clinically significant PCa were 6.1%, 33.3%, and 64.4% for PI-RADS 3,
4, and 5 respectively, and increased in proportion to the
score23. A study assessing 737 lesions with
MpMRI-targeted TRUS-bx found the PCa rates for PI-RADS 1, 2, 3, 4 and 5
lesions were 0%, 10%, 12%, 22% and 72%
respectively24. In our study, 22.2%, 56%, and
94.45% cancers were detected in PI-RADS 3, 4, and 5 groups
respectively. None of the malignant lesions in the PI-RADS3 group had
ISUP>1 pathology results. As in all PI-RADS versions,
disease management after scoring is not specified for patients in v2.1.
In PI-RADS v2.1, ”Category 3 lesions are of intermediate status with an
equivocal risk of presenting clinically significant prostate cancer
(csPCa)” risk is stated and there are limited studies in the literature
regarding the selection of follow-up-biopsy and it has not been
clarified yet9,25. Therefore, all PI-RADS-3 lesions
were biopsied with the clinician’s preference.
There was a positive correlation found between the PI-RADSv2.1 score
with the ISUP score(Table-6) (p<0.001). A study by
Walker et al.26 found a positive correlation between
PI-RADSv2.1 categories and ISUP groups with a correlation value of 0.5
and with the increase of the PI-RADS category, clinically significant
cancer rates were shown to increase. Additionally, as shown in the study
by Walker et al., also in our study, in PZ when lesions with DWI score 3
upgraded to PI-RADS4 group with DCE positivity and PI-RADS4 lesions with
DWI score 4 are compared, the PI-RADS4 lesions with DWI score 4 were
observed to have higher ISUP grades26. These results
clearly show that as the PI-RADSv2.1 score increases, the
clinically-significant cancer detection rate increases, and can be
interpreted as the tumors have more aggressive histopathology. However,
in our study, the histopathological evaluation of lesions observed
25.47% had ISUP>1, while 40.56% of lesions had PI-RADS
scores of 4 or 5. It is clear that PI-RADSv2.1 also needs improvements
and more objective recommendations, and further research may contribute
to achieving this aim. In our study, when cut-off values for PZ and
whole gland are accepted as PI-RADS≥3, the NPV for malignancy was
100.00%. For cut-off value PI-RADS≥4 lesions, this value was 76.47%
for PZ, 83.33% for TZ, and 80.65% for the whole gland, compatible with
the literature27–29. The high NPV is very important
in terms of excluding cancer for patients without performing bx. The
sensitivity, specificity, PPV, and NPV analysis in terms of PI-RADSv2.1
sequences and zones are summarized inTable-4 andTable-5 . However, no study in the
literature separately evaluated the sequences in PI-RADSv2.1. When we
compare with meta-analyses performed for PI-RADSv2, the sensitivity,
specificity, PPV, and NPV values for the sequences are compatible with
the previous studies30. A study comparing PI-RADSv2
and 2.1 calculated the diagnostic sensitivity, specificity, PPV, and NPV
for PI-RADSv2.1 according to PI-RADS≥3 are taken as positive for the
detection of GS≥7 tumors according to zones as 94.3%, 24.2%, 46.1%,
and 86.1% for PZ and 93.8%, 42.1%, 45% and 93% for TZ,
respectively31. In our study, taking the PI-RADS score
cut-off value as ≥3 positive for PZ, the sensitivity for PCa was 100%,
specificity was 11.11%, PPV was 46.67% and NPV was 100.00%, similar
to levels to the literature for PZ was observed. Although the PI-RADSv2
system is well standardized and expanded for MpMRI use, studies have
reported interobserver agreement is highly variable from low to
high32–34. A study with 3 observers by Popita et
al.35 found the interobserver agreement kappa
coefficient(κ) was 0.643, 0.664, and 0.568. A study which two
radiologists examined 170 patients, determined the interobserver
agreement for PI-RADS≥3 was substantial (all zones κ=0.63 PZ κ=0.62, TZ
κ=0.53) and for PI-RADS≥4 was almost perfect (all zones κ=0.91, PZ
κ=0.91, TZ κ=0.87)36. Smith et al.37found the interobserver agreement was fair with κ=0.24. The
compatibility degree between experienced observers was higher for the
whole gland and PZ lesions compared to the observers with moderate
levels of experience. When the sequence-specific interobserver agreement
is assessed, values were κ=0.24, 0.24, and 0.23 for T2W, DWI, and DCE
respectively. Between two radiologists with different levels of
experience, we observed moderate compatibility for the use of
PI-RADSv2.1 without the cut-off value(all zones κ=0.562) and the cut-off
value of PI-RADS≥4(all zones κ=0.77). Our data show that the use of the
new update to PI-RADSv2.1 increases interobserver agreement with more
specific definitions. Increasing observers’ experience and future
PI-RADS updates will increase the agreement power between inexperienced
observers or observers with similar experience.