What is the best imaging modality to ascertain prostate size?

From the Guidelines

Transrectal ultrasound (TRUS) is the best imaging modality to ascertain prostate size. This technique provides accurate measurements of prostate volume by capturing multiple cross-sectional images of the gland, which are then used to calculate its dimensions and overall volume. TRUS is preferred because it offers real-time imaging, is relatively inexpensive compared to other modalities, and does not expose patients to radiation 1. The procedure involves inserting a small ultrasound probe into the rectum, positioned close to the prostate gland, which typically takes only 10-15 minutes to complete under local anesthesia.

Key Points

• TRUS is a safe, inexpensive, effective, noninvasive, radiation-free imaging technique often used as the primary screening or diagnostic modality in men to evaluate the prostate gland and seminal tract 1.
• TRUS has shown utility in guiding transperineal aspiration of the seminal vesicles and has a high diagnostic accuracy when combined with transurethral seminal vesiculoscopy 1.
• The prostate volume is an important criterion for interventional treatment selection and can predict the risk of symptom progression and BPO-related complications 1.
• While MRI can also accurately measure prostate size and provides excellent soft tissue detail, it is more expensive, less accessible, and not necessary for basic size determination 1.
• Digital rectal examination can estimate prostate volume but is less accurate than ultrasonography (US) 1.

Clinical Practice

For clinical practice, TRUS measurements are typically reported in three dimensions (height, width, and length) with the volume calculated using the ellipsoid formula (length × width × height × 0.52), with normal prostate volume being approximately 20-30 cc in adult men. This information is crucial for guiding treatment decisions and predicting outcomes.

Recommendation

TRUS is the recommended imaging modality for ascertaining prostate size due to its accuracy, safety, and cost-effectiveness. It is essential to prioritize TRUS over other imaging modalities, such as MRI or CT scans, for basic size determination, unless specific indications require the use of these alternative modalities 1.

From the Research

Imaging Modalities for Prostate Size Measurement

• Transrectal ultrasonography (TRUS) is a commonly used imaging modality for measuring prostate size, as it provides detailed internal architecture and accurate measurements 2.
• TRUS has been compared to magnetic resonance imaging (MRI) in estimating prostate volume, with studies showing similar results between the two modalities 3, 4.
• TRUS is considered a preferred modality for follow-up of benign prostatic hyperplasia (BPH) patients due to its accuracy, cost-effectiveness, and user-friendliness 3.
• A study comparing TRUS and endorectal MRI (eMRI) found a strong linear relationship between the two modalities in estimating prostate volume, with TRUS being a reliable method for determining prostate-specific antigen (PSA) density 4.

Comparison of Ultrasound Modalities

• A comparison of transabdominal and transrectal ultrasound for sizing of the prostate found that transabdominal ultrasound (PUS) is interchangeable with TRUS for prostates ≤ 30 cm3, but TRUS or cross-sectional imaging is recommended for larger prostates 5.
• The use of MRI priors can improve prostate segmentation in TRUS images, particularly at the base and apex where the gland boundary is hard to define 6.

Key Findings

• TRUS is a reliable and accurate modality for measuring prostate size, with similar results to MRI 3, 4.
• TRUS is suitable for determining which patients should undergo active surveillance, based on prostate volume and PSA density 4.
• The choice of ultrasound modality (TRUS or PUS) depends on prostate size, with TRUS being recommended for larger prostates 5.