In patients who choose radical prostatectomy, MRI can provide invaluable information for surgical planning. By demonstrating the location, size, and extent of the cancer MRI helps the surgeon to avoid leaving positive surgical margins or unnecessarily damaging surrounding structures that are essential for the recovery of normal urinary and sexual function.

For example, with accurate information about the location of the cancer, the surgeon can modify the operation to resect more widely in areas of suspected extracapsular extension, or to dissect closer to the prostate in the areas of the neurovascular bundles when extracapsular extension appears unlikely. A study [37] of 76 patients showed that pre-operative reviews of endorectal MR images significantly improved the surgeon’s decisions regarding whether to preserve or resect the neurovascular bundles at radical prostatectomy (p

< 0.01). Similarly, by predicting the presence and location of seminal vesicle invasion, MRI can assist the surgeon in deciding whether to remove the seminal vesicles completely.

Magnetic resonance imaging can also be of assistance by demonstrating the location of cancer within the gland. For example, visualization of a large, anterior transition zone tumor on the pre-operative MRI will alert the surgeon to the need for more distal transection of the dorsal vein complex over the urethra

[38], whereas demonstration of a prominent tumor in the posterior apex will warn the surgeon to dissect more widely in that area.

Magnetic resonance imaging may help predict substantial intraoperative blood loss, as the prominence of the apical periprostatic veins on MRI has been positively associated with blood loss [39]. In addition, the length of the membranous urethra on coronal endorectal MRI can help to predict the time to recovery of urinary continence [40]. It has been found that patients with a longer than average (14 mm) membranous urethra experience a more rapid return to complete continence [40].

There is no question that lymph node metastasis is one of the most important negative prognostic factors in prostate cancer. For many years, CT was the only imaging modality used to identify lymph node metastases. The results were disappointing,  as detection depends on size criteria (generally,  a short-axis diameter greater than 7-8 mm), even though lymph node metastases may be present in normal-sized nodes or absent from enlarged nodes. The detection of metastatic lymph nodes by MRI depends on the same size criteria as CT and therefore is similarly limited, with high specificity but low sensitivity.

However, the use of MRI before treatment has the advantage of allowing the primary tumor and the pelvic lymph nodes to be assessed simultaneously. A recent study has shown that the prediction of lymph node metastasis by MRI improved when MRI findings for seminal vesicle invasion, extracapsular extension and nodal metastasis were combined in a model [41]. By identifying specific enlarged nodes that may harbor cancer and by helping to predict the pathologic tumor stage, and therefore the likelihood of lymph node metastasis, MRI can improve surgical planning and help determine whether systemic therapy should be administered before surgery. If radiation therapy is planned, MRI may help the radiation oncologist to decide whether the pelvic lymph nodes should be included in the radiation field.

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Hedvig Hricak and Peter T. Scardino
Prostate Cancer, eds. Hedvig Hricak and Peter T. Scardino. Published by Cambridge University Press.
© Cambridge University Press 2009.

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