From the Guidelines
Multiparametric prostate MRIs are graded using the Prostate Imaging-Reporting and Data System (PI-RADS), which standardizes reporting and communication of findings, as outlined in the most recent and highest quality study by the PI-RADS steering committee 1. The current version, PI-RADS v2, uses a 5-point scale to assess the likelihood that a lesion represents clinically significant prostate cancer.
- A score of 1 indicates very low likelihood of cancer
- A score of 2 suggests low likelihood
- A score of 3 represents equivocal findings
- A score of 4 indicates high likelihood
- A score of 5 signifies very high likelihood of clinically significant cancer. The grading incorporates findings from T2-weighted imaging, diffusion-weighted imaging (DWI), and dynamic contrast-enhanced (DCE) sequences, with different sequences given priority depending on the zone of the prostate being evaluated, as discussed in the European Urology study 1.
- For peripheral zone lesions, DWI is the primary determining sequence
- While T2-weighted imaging is most important for transition zone lesions
- DCE serves as a secondary sequence that can upgrade certain PI-RADS 3 lesions to PI-RADS 4. This standardized grading system helps urologists and radiologists make appropriate management decisions, including whether to perform targeted biopsies on suspicious lesions, particularly those graded PI-RADS 4 or 5, as supported by the expert consensus opinion from the PI-RADS steering committee 1.
From the Research
Grading of Multiparametric Prostate MRI Scans
Multiparametric prostate Magnetic Resonance Imaging (MRI) scans are graded using the Prostate Imaging Reporting and Data System (PIRADS) scoring system. The PIRADS scoring system assesses the likelihood of clinically significant prostate cancer.
PIRADS Scoring System
The PIRADS scoring system assigns a score from 1 to 5, with higher scores indicating a higher likelihood of clinically significant prostate cancer. The scores are defined as follows:
- PIRADS 1: Very low likelihood of clinically significant prostate cancer
- PIRADS 2: Low likelihood of clinically significant prostate cancer
- PIRADS 3: Intermediate likelihood of clinically significant prostate cancer
- PIRADS 4: High likelihood of clinically significant prostate cancer
- PIRADS 5: Very high likelihood of clinically significant prostate cancer
Association with Biopsy Results
Studies have shown that the PIRADS score is associated with biopsy results. For example, one study found that:
- PIRADS 2 lesions had a low incidence of clinically significant disease (12%) 2
- PIRADS 3 lesions had a 12% incidence of clinically significant disease 2
- PIRADS 4 lesions had a 51% incidence of clinically significant disease 2
- PIRADS 5 lesions had an 80% incidence of clinically significant disease 2
Diagnostic Accuracy
The PIRADS scoring system has been shown to have good diagnostic accuracy for detecting prostate cancer. One study found that the area under the curve (AUC) for detecting prostate cancer was 0.97 when combining all single modality scores 3. Another study found that the sensitivity and specificity of the PIRADS scoring system for detecting clinically significant prostate cancer were 84.3% and 53.3%, respectively, when using a cut-off score of ≥4 4.
Combination with Other Parameters
The PIRADS score can be combined with other parameters, such as prostate-specific antigen (PSA) density, to improve the prediction of biopsy outcome. One study found that a combination of PIRADS score and PSA density was associated with the highest clinically significant prostate cancer detection rates (76-97%) on the first biopsy 5.
Key Findings
Key findings from the studies include:
- The PIRADS scoring system is a useful tool for assessing the likelihood of clinically significant prostate cancer
- The PIRADS score is associated with biopsy results, with higher scores indicating a higher likelihood of clinically significant prostate cancer
- The PIRADS scoring system has good diagnostic accuracy for detecting prostate cancer
- Combining the PIRADS score with other parameters, such as PSA density, can improve the prediction of biopsy outcome 2, 3, 4, 5