Various imaging modalities are useful in management of prostate cancer patients. While ultrasound may be very useful in diagnostic biopsy, imaging scans like CT and MRI are useful for staging and treatment planning respectively. In presence of bone metastases, bone scan serves a scan for disease monitoring.

Transrectal ultrasound examination of the prostate is performed mainly to guide core biopsies to the prostate gland itself. It has very limited use for direct visualisation of the cancer. Currently in our institution, the prostate is divided arbitrarily into 10 zones and one core is randomly applied to each zone when prostate cancer is suspected from elevated PSA or abnormal per rectal examination.

Although MRI prostate gives an exquisite image of the gland, it is not routinely performed for staging prostate cancer. Staging of prostate cancer currently relies on a normogram ( Partin Tables, Urology 2001; 58:843-848 ) that predicts the risks of extraprostatic extension based on the findings of the per-rectal examination, PSA and histological Gleason score.

MRI prostate is useful in the setting of the patient with intermediate risks of extra-prostatic extension. The NCCN guidelines recommends pelvic CT or MRI in cases with evidence of extraprostatic extension on rectal examination (T3 and T4) and in cases of organ confined disease where the probability of lymph node involvement is more than 20%.

In general, MRI performed with endorectal coil is more accurate than those performed with surface coils. The endorectal coil resembles a foley’s catheter and is well tolerated. The examination takes about 30 to 45 minutes. MRI has a low sensitivity for extraprostatic extension as it cannot image microscopic spread. The specificity is, however, high.

D’Amico (J Urol 2000;164:759) has shown that MRI in the setting of the intermediate risk patient can stratify patients into two groups. Patients with MRI evidence of extraprostatic extension have higher risks of PSA failure after 5 years. Hence MRI is useful in selecting therapy in this group of patient.

Although a bone scan is sensitive for bony metastases, it is only indicated in patients with higher probability of extraprostatic extension: PSA is above 20ng/ml, or Gleason score 8 and above, or T3 or T4 on per rectal examination or symptomatic for bone pain.

Figure 1 Coronal T2-weighted scan of the prostate show seminal vesicle invasion (arrow) on the right.

Figure 2 Bone scan show widespread bony metastases including vertebrae and ribs in patient with advanced carcinoma of the prostate.

 

Thng Choon Hua
Senior Consultant
Department of Oncologic Imaging
National Cancer Centre, Singapore