Prostate biopsies are carried out in several different ways. The most commonly employed methods are transrectal ultrasound (TRUS) guided systematic biopsy of the prostate, transurethral biopsy and transperienal prostate biopsy.
TRUS-guided systematic biopsy of the prostate is considered to be the gold standard for the diagnosis of prostate cancer. The process may be done after sedation in most cases. The patient is asked to lie on the left side with the knees slightly drawn up, which relaxes and exposes the rectum. In this left lateral situation, the doctor inserts an ultrasound probe into the rectum. The probe is only as thick as an ordinary pencil, and does not cause more than slight discomfort or pressure.
Using the probe, the doctor obtains images of the prostate. This guidance enables the injection of a local anesthetic (generally 1-2% lidocaine) into the area around the prostate, to numb it by nerve. The needle may cause some pain, while the anesthetic produces a brief burning sensation, followed by numbness.
Still under ultrasound guidance, the doctor inserts an 18-gauge needle into several areas of the prostate to recover tissue samples from 10-18 areas. These are prepared for histologic examination. In the standard systematic biopsy, cores of tissue are taken from 12 sites. However, most of these are from the posterior part of the prostate. The anterior tumor foci are often not picked up because of the length of the needle (17 mm) which limits penetration into this part of the gland.
In about 10-20 minutes the patient is ready to leave the biopsy room. The greatest controversy surrounding this procedure has to do with its low sensitivity and the false-negative rate, which has been reported to be up to 20-30%.
Transurethral biopsy is a method that is used less often, but involves the insertion of a cystoscope. This is a flexible tube with a camera mounted on the end. This is passed through the urethra and tissue samples are recovered from the prostate through the urethral wall.
The transperineal biopsy (TPB) using points mapped to a brachytherapy template grid is becoming popular because of the better opportunity it offers to sample the prostate in a systematic manner. It especially adds to the accuracy of sampling of the anterior and transition zones, which often contain tumor foci that make up 25–55% of prostate cancer cases. These are the areas that are most often missed by TRUS biopsy. In addition, diagnosed cancers have been upgraded, or new cancer foci detected, in 26–36% of patients who have had a transperineal biopsy, after a prior TRUS biopsy.
The transrectal route of prostate biopsy may yield false-negatives to the extent of 20-30%. Many of these tumors are picked up by transperineal biopsy, and are situated in the anterior part of the prostate. This method allows better access to this part of the prostate, and thus rises the detection rate. The technique can be used even if the patient does not have a patent anus, due to prior surgery for rectal cancer.Leave a reply