What is the best ultrasound scan (USS) to assess prostate volume?

From the Guidelines

Transrectal ultrasound (TRUS) is the best ultrasound method to assess prostate volume. This technique involves inserting a specialized ultrasound probe into the rectum to obtain detailed images of the prostate gland from close proximity. TRUS provides accurate measurements of prostate dimensions (height, width, and length) which are used in the prolate ellipsoid formula (length × width × height × 0.52) to calculate the volume in cubic centimeters. The procedure typically takes 10-15 minutes and requires minimal preparation, though some practitioners may recommend an enema beforehand. TRUS is superior to abdominal ultrasound for prostate volume assessment because it eliminates interference from abdominal fat, bowel gas, and pelvic bones, resulting in clearer images and more precise measurements. This accuracy is crucial for clinical decision-making in conditions like benign prostatic hyperplasia, determining PSA density, and planning treatments such as radiation therapy or prostatectomy. While transabdominal ultrasound can estimate prostate size, it generally underestimates volume compared to TRUS, particularly for larger prostates.

Key Points

• TRUS is the preferred method for assessing prostate volume due to its accuracy and minimal interference from surrounding tissues 1.
• The procedure is relatively quick and requires minimal preparation.
• TRUS is essential for clinical decision-making in various prostate-related conditions, including benign prostatic hyperplasia and prostate cancer.
• The accuracy of TRUS is critical for determining PSA density and planning treatments such as radiation therapy or prostatectomy.

Comparison with Other Methods

• Transabdominal ultrasound can estimate prostate size but is generally less accurate than TRUS, particularly for larger prostates.
• Digital rectal examination can estimate prostate volume but is less accurate than ultrasonography (US) 1.
• Other imaging modalities, such as MRI, may be used in certain situations, but TRUS remains the gold standard for prostate volume assessment.

Clinical Implications

• Accurate assessment of prostate volume is essential for determining the best course of treatment for patients with prostate-related conditions.
• TRUS is a valuable tool for clinicians to make informed decisions about patient care.
• The use of TRUS can help reduce the risk of complications and improve patient outcomes.

From the Research

Comparison of Ultrasound Methods for Prostate Volume Assessment

• Transrectal ultrasound (TRUS) and transabdominal ultrasound are two common methods used to assess prostate volume 2.
• A study comparing TRUS and pelvic abdominal ultrasound (PUS) found that for prostates ≤ 30 cm3, PUS is interchangeable with TRUS in estimating prostate volume 2.
• However, for larger prostates, TRUS or cross-sectional imaging is recommended due to the potential for size to alter surgical management 2.

Accuracy of TRUS and MRI in Prostate Volume Measurement

• A study comparing TRUS and magnetic resonance imaging (MRI) found that MRI is more accurate than TRUS for determining prostate volume, but TRUS is almost as accurate and is less expensive and noninvasive 3.
• Another study found that prostate volume estimations with TRUS and endorectal MRI are highly correlated, and TRUS is an efficient and economical examination for estimating prostate size 4.
• A retrospective analysis comparing TRUS and MRI prostate volumes with prostate gross specimens found that MRI is more accurate than TRUS, but the difference is small, and TRUS remains an adequate imaging modality in patients with prostate cancer 5.

Formula for Estimating Prostate Volume

• A study evaluating different methods for estimating prostate volume found that the prolate spheroid formula is the most accurate method for estimating prostate weight, especially for glands weighing less than 40 gm or between 40-80 gm 6.
• The elliptical volume formula is also widely used, but it demonstrated a slightly lower correlation coefficient compared to the prolate spheroid formula 6.

Clinical Significance of Accurate Prostate Volume Measurement

• Accurate prostate measurements are key to preoperative planning of surgical interventions such as tissue resection or prostatectomy 5.
• A study highlighting the importance of accuracy in prostate measurements found that small differences in estimated prostate volume can have significant clinical implications 5.