The PIRADS (Prostate Imaging and Reporting and Data System) system is an important tool for prostate MRI evaluations. While mpMRI was introduced around 2005 (including 3 phases – T2 weighted images [T2W], diffusion weighted images [DWI] and dynamic contrast enhancement [DCE]), the first PIRADS reporting system was first introduced 2012. It was limited significantly by poor inter-observer and intra-observer variability – and therefore uptake was very poor. As a result, the ACR, ESUR and AdMeTech organizations generated a 2nd version (PIRADS v2) in 2014.
The aim of the PIRADS v2 is multi-fold – but the emphasis is simplifying/standardizing radiology reports and enhancing communication with urologists (clinicians). The limitations of the PIRADS specific protocols are that it is not great at detecting cancer following therapy, following progression of disease on surveillance, and looking for cancer metastases to bone and lymph nodes – other imaging modalities may be better for this.
He notes that his clinical considerations for patient scheduled for mpMRI of the prostate include:
- MRI scan should be done 3-6 weeks after biopsy to minimize biopsy effects (hemorrhage)
- Bowel inhibitor prior to scan (to limit bowel motion)
- Fasting for 6 hours
- He does NOT think rectal evacuation with enema is necessary – but the other speakers disagreed. They felt bowel gas was a big limitation.
- Patient information is critical for the radiologist – PSA, DRE, and prior biopsy results
Typically there are 3 phases: T2W, DCI, DCE
- T2W is the main sequence for transitional zone (TZ) tumors
- DCI is the main sequence for peripheral zone (PZ) tumors
- T1W images (from prostate to aortic bifurcation) is useful for local staging (bone, soft tissue)
- DCE is under attack – many are considering excluding it, but he still finds it very useful
- In PZ tumors, it can help stratify PIRADS 3 lesions on DWI into PIRADS 3 or 4
- Highest quality with 3T and endorectal coil
- Lowest quality with 1.5T and surface coil
- This should be accounted for in the grading of lesions and clinical decision making
- Only PIRADS 4-5 lesions should be biopsied
- However, this is institution and image quality dependent
- PIRADS 3 lesions should be biopsied if poor imaging quality (may be PIRADS 4 on better images)
The way PIRADS v2 is set-up, PIRADS 4 and 5 are high / very high risk of having clinically significant prostate cancer. PIRADS 3 is intermediate risk – and is the most ambiguous definition!
PIRADS assessment with DWI:
- PIRADS 4 = focal markedly hypointense on ADC and markedly hyperintense on high b-value DWI, <1.5 cm in greatest dimension
- PIRADS 5 = same as PIRADS 4, but > 1.5 cm or evidence of local extension/aggressive disease (ECE)
- PIRADS 4 = lenticular or non-circumscribed, homogenous, moderately hypointense and <1.5 cm in dimension
- PIRADS 5 = same as PIRADS 4, but > 1.5 cm or evidence of local extension/aggressive disease (ECE)
PIRADS assessment with DCE (if used):
- Positive DCE: focal and earlier than enhancement of adjacent tissue
1. The highest PIRADS category lesion
2. If 2 or more lesions exist, it should be the one that shows ECE or is the largest
His take-home points:
1. Learning PIRADS v2 scoring and reporting helps you detect and biopsy significant cancer more effectively
2. Urologists, especially those involved in prostate biopsies, should be familiar with mpMRI features of PIRADS system!
This second point was a recurring theme of the Master Class!
Presented by: Byung Kwan Park, South Korea
Written By: Thenappan Chandrasekar, MD, Clinical Instructor, Thomas Jefferson University Twitter: @tchandra_uromd, @TjuUrology at the 38th Congress of the Society of International Urology - October 4- 7, 2018 - Seoul, South Korea