Transrectal ultrasound

Transrectal ultrasound (TRUS) is a technique that is used most commonly to evaluate

• the prostate gland, including ultrasound-guided prostate biopsies
• depth of invasion of colon/rectal cancer (for staging purposes)

It can also be used for guidance in placing a transrectal drain, or in rare problem-solving situations in which pelvic organs are inadequately evaluated with a transabdominal approach and the transvaginal approach is not possible or not preferred.

Its utility in evaluating the prostate gland is analogous to transvaginal imaging in women. The ultrasound probe is placed as close as possible to the organ of interest, allowing a higher frequency probe to be employed with a subsequent improvement in spatial resolution.

Procedure

Equipment

Transrectal imaging usually employs a higher-frequency 8-10 MHz probe with a long transducer length, similar to a transvaginal probe.

Technique

A typical diagnostic prostate scan usually involves

1. many institutions ask a patient to use a suppository before the exam to ensure that his or her rectum is empty before scanning
2. immediately before the exam, counseling the patient about the reason for the technique and what they can expect
   • even if this is a routine procedure for the radiologist, this is very often an unwelcome and invasive procedure for the patient and a little discussion beforehand is often very helpful
   • a chaperone in the room is useful
3. correct patient positioning: patient in a decubitus position with knees tucked up toward the chest
4. visually inspect the anus and perineal area before introducing the transducer, looking for anything that may hinder the procedure (hemorrhoids, anal issue, dermatologic conditions, etc.). Some advocate a quick preliminary digital rectal exam
5. the transducer will be covered with a plastic sheath (with gel on the inside). Use a liberal amount of gel on the transducer end outside of the plastic sheath as well.
6. introduce the transducer slowly through the anus, using gentle pressure. There will likely be a small amount of resistance at the anal sphincter, but one should not have to shove the transducer, and if you are encountering too much resistance, the transducer tip may be mispositioned against the perineum
7. the prostate should be visible relative quickly after passing the anal sphincter i.e. do not put too much of the transducer into the rectum.
8. one passing the anal sphincter and visualizing the prostate, you do not have to apply as much pressure, and too much pressure may actually make it difficult to visualize the peripheral zone of the prostate. Once you see the prostate, try easing off on the pressure to see if the image improves

Prostate biopsy transrectal ultrasound shares many of the similar techniques, but they may be modified to fit difference in patient positioning, urologist preference, etc.