MULTI-PARAMETRIC MRI PROSTATE
MULTI-PARAMETRIC MRI PROSTATE
In adults Prostate cancer is the second most common cancer and the commonest in men.
Factors that increase the risk of prostate cancer include: older age, a family history (having a first degree relative increases the risk 2 fold), and race. The majority of cases occur in those over the age of 50. Prostate cancer is asymptomatic in the majority of patients and the symptoms men often suffer with frequency and urgency of micturition and nocturia known as lower urinary tract symptoms (LUTs) are usually due to benign prostate hyperplasia (BPH).
The diagnosis of prostate cancer is based on clinical examination of the prostate and prostatic specific antigen (PSA) testing. Other serology tests are available e.g PCA-3 gene. The current diagnosis is based on prostate biopsy, typically 12 samples of the gland taken via the rectum (transrectal ultrasound TRUS), and examination under the microscope to grade the cancer using a Gleason score. Significant prostate cancer is defined as Gleason 7 and above and active treatment is required for these cases as advised by specialised urologists and oncologists.
Prostate biopsy unfortunately only samples a very low percentage in terms of volume of the gland and can miss significant disease within the gland especially at the front of the gland. Transperineal template biopsy can help in this matter but can involve 30-50 samples under a GA. Imaging of the prostate gland has a role to identify potential areas of significant disease that can be targeted for biopsy. This has the advantage of reducing the number of biopsies required and therefore reducing the risks, particularly infection.
Multi-parametric MRI Prostate (mpMRIP)
This is a special MRI technique to image the prostate and uses anatomical (identifying a focal abnormality) and functional (identify likelihood of cancer) sequences. The advantages of this technique are that it is non-invasive, can accurately record the size of the prostate gland and identify significant prostate cancer, if the volume is above 0.5cm3 (7mm lesion). It also can clearly identify the front of the gland and the apex (lowest point) and identify the likelihood of any spread outside the gland.
There are many publications now demonstrating the accuracy and safety of mpMRIP but a recent study called PROMIS compared TRUS and biopsy to mpMRIP. It showed that TRUS & biopsy performs poorly in detecting and ruling out significant prostate cancer but that mpMRIP used as a triage test in men with a raised PSA could avoid unnecessary biopsy without the detection of clinically significant cancer in 25% of men. This therefore avoids all the complications associated with TRUS biopsy especially infection and prostatitis.
As the complexity of the technology becomes more advanced it is common in tertiary and quaternary hospitals that radiologists become more subspecialised in specific areas of medicine e.g. urogenital radiologist, gastrointestinal radiologist.
A completely normal mpMRIP can therefore be very reassuring that there is no significant prostate cancer and can help you make the decision if you need a TRUS biopsy or could be followed up with PSA measurements and interval mpMRIP’s.
Who should have mpMRI Prostate imaging?
This area is a little controversial and is a fast moving area of medicine. There is an argument that every man being considered for a TRUS and biopsy should have an MRI performed prior. There are a couple of reasons for this: 1. It can identify focal areas that can be biopsied in addition which commonly leads to a more accurate identification of grade and 2. Biopsy can lead to artifacts on MRI, which significantly reduces the accuracy of the imaging test.
Indications that are less contentious are the following:
- Previous normal TRUS and biopsy with rising PSA measurement
- Low risk prostate cancer considering active surveillance
- Known small focus of high risk prostate cancer on surveillance
- Local staging of a large focus of prostate cancer
- Consideration for local ablative therapies.