Section V: Staging
MRI is useful for determination of the T stage, either confined to the gland (< T2 disease) or extending beyond the gland (> T3 disease).
The apex of the prostate should be carefully inspected. When cancer involves the external urethral sphincter, there is surgical risk of cutting the sphincter, resulting in compromise of urinary competence. Tumor in this region may also have implications for radiation therapy.
High spatial resolution T2W imaging is required for accurate assessment of extraprostatic extension (EPE), which includes assessment of neurovascular bundle involvement and seminal vesicle invasion. These may be supplemented by high spatial resolution contrast-enhanced fat suppressed T1W.
The features of seminal vesicle invasion include focal or diffuse low T2W signal intensity and/or abnormal contrast enhancement within and/or along the seminal vesicle, restricted diffusion, obliteration of the angle between the base of the prostate and the seminal vesicle, and demonstration of direct tumor extension from the base of the prostate into and around the seminal vesicle.
Imaging features used to assess for EPE include asymmetry or invasion of the neurovascular bundles, a bulging prostatic contour, an irregular or spiculated margin, obliteration of the rectoprostatic angle, a tumorcapsule interface of greater than 1.0 cm, breach of the capsule with evidence of direct tumor extension or bladder wall invasion.
The next level of analysis is that of the pelvic and retroperitoneal lymph nodes. The detection of abnormal lymph nodes on MRI is currently limited to size, morphology and shape, and enhancement pattern. In general, lymph nodes over 8mm in short axis dimension are regarded as suspicious, although lymph nodes that harbor metastases are not always enlarged. Nodal groups that should be evaluated include: common femoral, obturator, external iliac, internal iliac, common iliac, pararectal, presacral, and paracaval, and para-aortic to the level of the aortic bifurcation.
Images should be assessed for the presence of skeletal metastases.