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|MRI-US fusion biopsy|
3d-reconstructed prostate gland indicating suspicious lesions for targeted biopsy. An informative video detailing the process of MRI-US fusion targeted biopsy can be found at the following website: http://urology.ucla.edu/body.cfm?id=455
Prostate biopsy is a procedure in which small needle-core samples are removed from a man's prostate gland to be examined microscopically for the presence of cancer. It is typically performed when the result from a PSA blood test rises to a level that is associated with the possible presence of prostate cancer. It may also be triggered by an abnormal digital rectal exam (DRE). PSA screening is controversial, and PSA may also be elevated by a benign enlargement of the (BPH, benign prostatic hyperplasia), by infection, or by manipulation of the prostate through surgery or catheterization.
The procedure, usually done as an outpatient, requires a local anesthetic; some men do report discomfort during the biopsy. The most frequent side effect of the procedure is blood in the urine or stool for several days or blood in the ejaculate possibly for several weeks afterwards. These side effects are usually self-limited and do not require additional treatment.
The procedure may be performed transrectally, through the urethra or through the perineum. The most common approach is transrectally, and historically this was done with tactile finger guidance. The most common method of prostate biopsy currently is transrectal ultrasound-guided prostate (TRUS) biopsy.
Extended biopsy schemes take 12-14 cores from the prostate gland through a thin needle in a systematic fashion from different regions of the prostate.
Antibiotics are usually prescribed to minimize the risk of infection. An enema may also be prescribed for the morning of the procedure. In the transrectal procedure, the doctor inserts an ultrasound probe into the rectum to help guide the biopsy needles. A local anesthetic is then administered into the tissue around the prostate, similar to the local anesthetic administered for a dental procedure. A spring-loaded prostate tissue biopsy needle is then inserted into the prostate. It makes a clicking sound, and, if local anesthetic is satisfactory, discomfort is minimal.
In a large multicenter study of 2,299 patients examining cancer detection rates via various biopsy schemes, a 12-site biopsy scheme outperformed all other schemes, with an overall detection rate of 44.4%. PSA levels were directly correlated with cancer detection rates, ranging from 19% in patients with PSA <2, up to 68% inpatients with PSA >20.
However a negative biopsy does not ensure the absence of disease. Systematic TRUS biopsy is "blind" since prostate cancer cannot often be seen with ultrasound. This problem is exacerbated in patients with larger prostate glands. In a 14-site biopsy, the additional cores are often taken at apical and anterior regions, a common site of "missed" tumors.
Initial biopsies can miss 20–30% of clinically significant cancers. Thus, negative biopsies in men with persistently elevated PSA levels are often followed by subsequent biopsies. With each additional biopsy session, the rate of cancer detection decreases.
Since the mid-1980s, TRUS biopsy has been used to diagnose prostate cancer in essentially a blind fashion because prostate cancer cannot be seen on ultrasound due to poor soft tissue resolution. However, multiparametric MRI has since the mid-2000s been used to better identify and characterize prostate cancer. A study correlating MRI and surgical pathology specimens demonstrated a sensitivity of 59% and specificity of 84% in identifying cancer when T2-weighted, dynamic contrast enhanced, and diffusion-weighted imaging together. Many prostate cancers, missed by conventional biopsy, are detectable by MRI-guided targeted biopsy.
Two methods of MRI-guided, or “targeted” prostate biopsy, are available: (1) direct "in-bore" biopsy within the MRI tube, and (2) fusion biopsy using a device that fuses stored MRI with real-time ultrasound (MRI-US). Visual or cognitive MRI-US fusion have been described.
When MRI is used alone to guide prostate biopsy, it is done by an interventional radiologist. Correlation between biopsy and final pathology is improved between MRI-guided biopsy as compared to TRUS.
In the fusion MRI-US prostate biopsy, a prostate MRI is performed before biopsy and then, at the time of biopsy, the MRI images are fused to the ultrasound images to guide the urologist to the suspicious targets. Fusion MRI-US biopsies can be achieved in an office setting with a variety of devices.
MRI-guided prostate biopsy appears to be superior to standard TRUS-biopsy in prostate cancer detection. Several groups in the U.S., and Europe, have demonstrated that targeted biopsies obtained with fusion imaging are several times more likely to reveal cancer than blind systematic biopsies. The more suspicious the MRI, the greater the likelihood of cancer on targeted biopsy. Considerable experience is required by the reader of prostate MRI studies. MRI scoring systems, to assign degree of cancer suspicion, have been described and will undoubtedly evolve as experience with the new modality increases.
Up to 2013, indications for targeted biopsy have included mainly patients for whom traditional TRUS biopsies have been negative despite concern for rising PSA, as well as for patients enrolling in a program of active surveillance who may benefit from a confirmatory biopsy with the added confidence of more accurate staging. Increasingly, men undergoing initial biopsy are requesting targeted biopsy, and thus, the use of pre-biopsy MRI is growing rapidly.
NIH-funded studies are underway to further clarify the benefits of targeted prostate biopsy.
The tissue samples are then examined under a microscope to determine whether cancer cells are present, and to evaluate the microscopic features (or Gleason score) of any cancer found. Gleason score, PSA, and digital rectal examination together determine clinical risk, which then dictates treatment options.
Tissue samples can be stained for the presence of PSA and other tumor markers in order to determine the origin of malignant cells that have metastasized.