Most men with prostate cancer have an MRI scan as part of their diagnosis. That scan remains useful long after the biopsy. Before a robotic prostatectomy, surgeons study it closely to plan the operation. It helps them balance two goals: removing all of the cancer and protecting the structures that control continence and erections.
What the MRI shows
A modern prostate MRI gives a detailed picture of:
- where the cancer sits within the prostate
- how close it is to the outer edge, or capsule
- whether it may have grown through the capsule
- whether it involves the seminal vesicles
- the size and shape of the prostate
- the length of the urethra below the prostate, which is linked to continence
Our guide to mpMRI scans explains how these images are produced.
Planning nerve-sparing
The nerves that control erections run in bundles along each side of the prostate. If the cancer is well inside the gland, the surgeon may be able to separate these nerves and preserve them. If the cancer is close to or beyond the capsule on one side, the surgeon may need to remove more tissue on that side to make sure no cancer is left behind.
MRI helps the surgeon decide, for each side:
- Full nerve-sparing: the nerves are kept intact.
- Partial nerve-sparing: some tissue is removed with the prostate, preserving part of the nerve bundle.
- No nerve-sparing: the nerves are removed with the prostate to give the best chance of removing all the cancer.
Our article on nerve-sparing robotic prostatectomy explains what this means for recovery.
Planning for continence
MRI can show the length of the membranous urethra, the short section below the prostate that contains part of the continence muscle. Men with a longer section tend to regain bladder control more quickly after surgery. Knowing this in advance helps the surgeon preserve as much length as is safe, and helps set realistic expectations.
Avoiding positive margins
A positive margin means cancer cells are found at the edge of the removed tissue. MRI helps the surgeon identify areas where the cancer is close to the edge, so extra care can be taken there. This reduces the chance of leaving cancer behind. Your pathology report after surgery will confirm whether the margins are clear.
Using MRI during surgery
Some surgical robots can display MRI images on the console screen alongside the live view. In some centres, the MRI is also used to create a 3D model of the prostate, either on screen or as a printed model, to help the surgeon visualise the tumour. These approaches are developing quickly and are not yet routine everywhere.
Lymph nodes and staging
MRI, sometimes combined with a PSMA PET scan, helps assess whether the lymph nodes may be involved. This affects whether lymph nodes are removed during surgery. Our article on combining MRI and PSMA PET scans explains how these scans work together.
The final decision
MRI is an important guide, but the final decisions are made during the operation, based on what the surgeon sees and feels. Techniques such as frozen section analysis, where tissue is checked under the microscope during surgery, can also help. Our article on the SAFE technique describes an approach to nerve-sparing.
Questions to ask
- What does my MRI show about the position of the cancer?
- Do you expect to be able to spare the nerves on both sides?
- Does the scan tell you anything about my likely continence recovery?
NICE guidance on prostate cancer covers the role of MRI, and Prostate Cancer UK explains the scan for patients.
Professor Prokar Dasgupta reviews each patient's MRI in detail when planning surgery at The London Clinic. Please contact the clinic to arrange a consultation.