A transrectal ultrasound (TRUS) is a specialized medical imaging technique that uses sound waves to create detailed pictures of organs and structures located near the rectum. This procedure is most often performed to examine the prostate gland in men, which is situated directly in front of the rectum. By employing high-frequency sound, TRUS allows healthcare providers to visualize the size, shape, and internal structure of these tissues. It is a minimally invasive method for assessing conditions that cannot be adequately evaluated through external physical examination alone.
Understanding the Transrectal Ultrasound Mechanism
Transrectal ultrasound technology operates on the principle of sound wave reflection to generate real-time images. The procedure utilizes a specialized, finger-sized device called a transducer, which is gently inserted into the rectum. This transducer emits high-frequency sound waves, typically in the range of 8 to 10 megahertz, into the surrounding pelvic tissues.
When these sound waves encounter different tissue densities, they bounce back as echoes. The same transducer then captures these returning echoes, which are immediately processed by a computer system. This processing translates the echo patterns into a dynamic, two-dimensional image displayed on a monitor, allowing the clinician to observe the internal organs as the scan is performed.
The transrectal approach is chosen because it places the transducer in direct and close proximity to the structures of interest, most notably the prostate and seminal vesicles. This short distance allows the use of higher-frequency sound waves than those used in a traditional external ultrasound. Higher frequency waves provide superior resolution and image clarity, which is necessary for detecting subtle abnormalities within the prostate tissue.
Preparing for and Undergoing the Scan
Preparation for a transrectal ultrasound focuses on ensuring the rectum is clear for optimal image quality and reducing the risk of infection, particularly if a biopsy is planned. Patients are often instructed to perform a small cleansing enema one to four hours before the appointment to clear the lower bowel of stool and gas. Because of the potential for bacterial transfer during the procedure, a course of antibiotics may be prescribed to be taken before, and sometimes after, the scan.
Upon arriving for the procedure, patients are usually asked to empty their bladder immediately before the scan begins. This is done because a full bladder can sometimes obstruct the view of the prostate gland. The patient is typically positioned lying on their side, often the left, with their knees bent up toward their chest, a posture that helps relax the abdominal and pelvic muscles.
The clinician applies a clear lubricating gel and a protective cover to the transducer before gently inserting it a short distance into the rectum. Patients may feel a sensation of pressure or fullness, similar to needing a bowel movement, but significant pain is uncommon. The entire diagnostic scan is typically completed within a relatively short timeframe, often taking only 15 to 30 minutes.
Primary Diagnostic Indications
Transrectal ultrasound is frequently utilized as a diagnostic tool following abnormal results from initial screening tests, such as an elevated prostate-specific antigen (PSA) blood test or a suspicious finding during a digital rectal exam (DRE). It allows for a detailed visual assessment of the prostate gland. The scan provides a means to accurately measure the volume and size of the prostate, which is an important factor in diagnosing and monitoring benign prostatic hyperplasia (BPH), a common non-cancerous enlargement of the gland.
The procedure helps identify structural changes within the prostate tissue, such as the presence of masses, cysts, or calcifications. Clinicians look for areas that appear hypoechoic, meaning they produce fewer echoes than surrounding normal tissue, which can sometimes indicate the presence of a tumor. However, because the appearance of cancerous tissue can overlap with benign conditions, TRUS alone cannot definitively diagnose cancer.
TRUS is also employed to examine the seminal vesicles, which are glands located behind the bladder that produce fluid for semen. The high-resolution images can reveal inflammation, cysts, or signs of obstruction in these structures, which may be a factor in male infertility or other pelvic symptoms. Furthermore, the scan can be used to assess for suspected infection, such as prostatitis or a prostatic abscess, by observing changes in tissue texture and fluid collections.
Guiding Biopsies and Interventional Procedures
Beyond its purely diagnostic function, the real-time imaging capability of transrectal ultrasound makes it an effective navigational tool for various interventional procedures. The most common use is to guide a prostate biopsy, a procedure necessary to obtain tissue samples for microscopic examination. During a TRUS-guided biopsy, the ultrasound image is used to precisely direct a fine, hollow needle into specific regions of the prostate gland.
This guidance ensures that tissue is collected either from areas that appear suspicious on the ultrasound or from systematic locations across the gland to minimize the chance of missing a small tumor. In modern practice, this process is often refined by fusing the live TRUS image with a prior magnetic resonance imaging (MRI) scan. This fusion allows for highly targeted sampling of previously identified lesions. Typically, a local anesthetic is injected to numb the prostate area before the needle insertion to minimize discomfort.
TRUS also serves as a guide for therapeutic treatments for prostate conditions. For instance, it can be used to navigate the precise placement of radioactive seeds during brachytherapy, a form of internal radiation used to treat prostate cancer. Other interventional applications include guiding the placement of instruments for cryotherapy, which uses extreme cold to destroy abnormal tissue, or for the drainage of pelvic abscesses near the rectum.