Transrectal Ultrasound (TRUS)

July 1, 2024

This page was reviewed under our medical and editorial policy by Wesley Yip, M.D., assistant professor, Division of Urology and Urologic Oncology, Department of Surgery, City of Hope^® Cancer Center Duarte

A transrectal ultrasound (TRUS) is a key tool for evaluating the prostate gland. During the procedure, high-energy sound waves are bounced off the body’s internal organs. The echoes of these sound waves help to form a sonogram, or picture of the inside of the body.

A TRUS may also be called a prostate ultrasound, endorectal ultrasound or ERUS.

The imaging test typically takes about 10 minutes to perform in a doctor’s office or outpatient clinic.

Transrectal ultrasound may be used to help diagnose prostate cancer or during or after prostate cancer treatment.

Why Is a Prostate Ultrasound Performed?

A transrectal ultrasound may be ordered for several reasons including:

• Abnormal results on a prostate-specific antigen (PSA ) test (a blood test used to screen for prostate cancer)
• An abnormality that was felt during a digital rectal exam (DRE)
• A suspected inflammation or infection of the prostate
• Lower urinary tract symptoms that might indicate prostate overgrowth (benign prostatic hyperplasia)
• Abnormalities seen on imaging of the abdomen that require investigation

A prostate ultrasound allows medical providers to evaluate the gland’s size, shape and the way it reflects sound waves. It is also used to assess structures and blood vessels around the prostate for anything unusual and to guide a needle during a biopsy of the prostate.

TRUS With Biopsy

A transrectal ultrasound alone does not reliably show the difference between normal tissue and cancerous tissue, so health care providers often perform a biopsy during the ultrasound to obtain samples of the prostate tissue.

During a biopsy, the doctor uses ultrasound to look at the prostate and then inserts a thin, hollow needle into the gland through the wall of the rectum. When the needle is withdrawn, it brings with it a small sample of prostate tissue.

In other cases, the care team may recommend a transperineal biopsy, which uses a transrectal ultrasound, but then the biopsy needles pass through the skin under the scrotum and not through the rectal wall.

Typically, about 12 samples from different areas of the prostate are collected. A pathologist then examines these samples under a microscope, looking for abnormal cells.

A TRUS with biopsy may take 20 to 30 minutes in a doctor’s office or outpatient clinic.

Preparing for a Transrectal Ultrasound

Typically, little to no advance preparation is required before a transrectal ultrasound. Some providers may have patients use a suppository or an enema before the procedure to remove stool from the rectum. This preparation is not universal, however.

If a biopsy is planned, the patient may be asked not to eat or drink for a few hours before the procedure. Patients may also be directed to avoid medications or dietary supplements that could increase the risk of bleeding. To reduce the risk of infection, the patient may be prescribed antibiotics to take before the biopsy and possibly for a few days afterward.

How Is an Ultrasound of the Prostate Performed?

At the ultrasound appointment, patients are asked to sign consent forms and will have an opportunity to ask any questions they have. Then, they will be asked to remove their clothing from the waist down or change into a hospital gown. This is what patients may expect during the procedure:

• They will be asked to lie on an exam table on their left side, with knees pulled up toward their chest.
• A digital rectal exam will be performed to ensure there is nothing, such as a mass or hemorrhoids, that might interfere with the test.
• The ultrasound probe is covered in a plastic sheath and well lubricated with a clear gel.
• The probe is inserted gently into the rectum.
• The provider uses the probe to scan the prostate from several angles.
• When the provider has finished scanning, the probe will be removed. The patient will be able to wipe off any excess gel and get dressed.

Is Transrectal Ultrasound Painful?

Patients who have a prostate ultrasound may feel some discomfort, similar to that felt during a digital rectal exam, but it is typically not painful. In some cases, the area may be numbed before the procedure. There are no known complications from a transrectal ultrasound.

If the patient is scheduled to have a prostate biopsy at the same time as the TRUS, they may receive a local anesthetic to block any pain in the area during the procedure. After the biopsy, there is a small risk of minor bleeding or infection, which may cause discomfort or pain.

What to Expect After TRUS

Patients typically leave soon after the test.

The provider will give the patient follow-up instructions. After a transrectal ultrasound, patients may drive and return to their usual activities.

If a biopsy is performed, the patient may be instructed to take antibiotics to reduce the risk of infection. After a biopsy, there may be some soreness and light bleeding. The patient may also have rust-colored semen when ejaculating for a few weeks.

If a biopsy was performed during the transrectal prostate ultrasound, a pathologist will issue a report stating whether any abnormal or cancerous cells were found. This typically takes a few days, but it may be longer.

Once the provider receives the results of the transrectal ultrasound and biopsy (if any), they will meet with the patient to discuss them and go over treatment options or next steps.