Arterial-phase, multisection CT scanning can help to differentiate between prostate PZ and prostate TZ regions, but it cannot demonstrate intraprostatic pathology. However, it may be helpful in detecting lymph node involvement.
CT and MRI scans depict lymph node enlargement and have similar accuracy for the evaluation of lymph node metastases. However, nodal staging relies on assessment of lymph node size, and neither CT scan nor MRI can demonstrate cancer within lymph nodes that are not enlarged.
CT scanning can also be used to stage the primary tumor, by depicting extracapsular spread in patients in whom advanced disease is suspected, particularly when radiation therapy is planned.
CT scan studies cannot depict T1 or T2 tumors accurately, but invasion of periprostatic fat or seminal vesicles by T3 tumors may be demonstrated.
Evidence-based guidelines for the use of CT scanning in prostate cancer staging have been produced. CT scanning may also be used to depict soft-tissue metastases elsewhere in the body. The CT scans below depict metastatic prostate cancer.
Axial computed tomography (CT) scan at the level of the kidneys shows extensive para-aortic lymphadenopathy (arrows), which results from advanced prostate cancer.
Metastatic prostate cancer (arrows) involves the soft tissues at the right side of the skull base. The patient presented with right-sided cranial nerve–XII palsy.
Previous studies have shown that digital rectal examination (DRE) and imaging techniques cause the understaging of cancer localized within the prostate. The most accurate imaging technique for staging prostate cancer appears to be endorectal MRI, but even this may cause significant understaging in approximately 30% of prostate cancers.
Because staging with CT scanning is performed by assessing the outline of the prostate, there should be little diagnostic confusion if an overt capsular breach is apparent. However, cancer is understaged by using CT scanning because the scans may fail to demonstrate microscopic spread through the prostatic capsule. This spread may be particularly difficult to assess at the apex and base of the prostate.