Transrectal ultrasound (TRUS) of the prostate is performed for volume measurement, guided biopsy, treatment planning (brachytherapy), and evaluation of prostate pathology. While many institutions have moved toward MRI-guided biopsy for cancer detection, TRUS remains common for volume assessment and biopsy guidance. Here's what sonographers need to know.

Indications

Prostate volume measurement (for PSA density calculation, BPH management, brachytherapy planning)
TRUS-guided prostate biopsy (elevated PSA, abnormal DRE, suspicious MRI lesion)
Evaluation of prostate abscess, seminal vesicle pathology, or ejaculatory duct obstruction
Evaluation of hematospermia

Equipment and Patient Preparation

Probe: Biplane endorectal (end-fire and side-fire) transducer, 7–10 MHz

Patient preparation:

Fleet enema 1–2 hours before the procedure (clears the rectal vault of stool, which impairs visualization)
NPO not required unless sedation planned
Antibiotic prophylaxis if biopsy planned (per institutional protocol, often a fluoroquinolone or other broad-spectrum agent given 30–60 min before)
Anticoagulants: Aspirin and NSAIDs often held several days before biopsy (discuss with ordering provider)

Patient position: Left lateral decubitus with hips flexed to 90° or greater (fetal position). This opens the anal canal and allows comfortable probe insertion.

Probe Insertion and Patient Communication

Explain the procedure clearly before insertion. The patient will feel pressure but should not feel sharp pain. Use generous amounts of lubricating gel on the probe cover (use a probe cover — sterile condom-style cover with sterile gel inside).

Insert gently, rotating as needed to navigate the rectal curve. The prostate will be anterior to the probe once properly positioned.

Normal Prostate Anatomy

Zonal anatomy (McNeal model):

Peripheral zone (PZ): 70% of prostate glandular tissue. Most prostate cancers arise here. Appears isoechoic, homogeneous, surrounding the central gland.
Central zone (CZ): Surrounds the ejaculatory ducts, base of prostate. Resistant to disease.
Transition zone (TZ): Periurethral glands. Site of BPH. The TZ grows with age. Appears as the inner gland, often heterogeneous due to BPH nodules.
Anterior fibromuscular stroma: Non-glandular, anterior surface.

Seminal vesicles: Paired structures superior to the prostate base. Normally hypoechoic, lobulated, with thin walls. Measure approximately 3 cm in length and 1–1.5 cm in width.

Ejaculatory ducts: Run through the central zone to the verumontanum. Normally not visible unless dilated.

Normal Echogenicity

Peripheral zone: Homogeneously isoechoic to slightly hyperechoic compared to the transition zone. Uniform texture.

Transition zone: More heterogeneous — BPH nodules cause mixed echogenicity (hypo and hyperechoic areas). This is normal in older men.

The boundary between TZ and PZ is called the "surgical capsule" — echogenic in some patients, best seen in the sagittal plane.

Prostate Volume Calculation

Volume is calculated using the prolate ellipse formula:

Volume (cc) = Length × Width × Height × 0.523

Where:

Length = AP dimension (measured in the sagittal plane)
Width = transverse diameter (measured in transverse plane at widest point)
Height = craniocaudal dimension (measured in the sagittal plane, from base to apex)

Normal prostate volume: < 30 cc in men under 50. Volume increases with age — 30–50 cc is common in older men; > 80 cc is significantly enlarged.

PSA density = PSA / prostate volume. PSA density > 0.15 is considered elevated and associated with higher cancer risk.

Systematic Scanning Protocol

Sagittal plane: Begin in midsagittal and sweep laterally to each side. Evaluate the central gland, urethra, peripheral zone in sagittal.

Transverse plane: Begin at the base (seminal vesicles come into view), sweep inferiorly through the mid-gland to the apex. The transverse plane is most useful for volume calculation (width and height).

Key images to document:

Sagittal midline (with length measurement)
Transverse at widest point (with width and height measurements)
Seminal vesicles bilaterally
Any focal lesion (two perpendicular planes, with size)

Pathological Findings

BPH (Benign Prostatic Hyperplasia):

Enlarged transition zone with heterogeneous, nodular texture
Well-defined echogenic "BPH nodules"
Enlarged prostate volume (> 30 cc, often 60–100+ cc in symptomatic patients)
Median lobe hypertrophy may protrude into the bladder — document if present

Prostate cancer:

Classic appearance: hypoechoic lesion in the peripheral zone
However: up to 30–40% of prostate cancers are isoechoic and not visible on TRUS
Hypervascular lesion on Doppler (asymmetric vascularity in PZ)
Any PZ lesion, particularly if associated with asymmetric vascularity, warrants biopsy correlation

Prostate cyst:

Utricle cyst: midline, near verumontanum — congenital
Müllerian duct cyst: midline, extends superior to prostate
Ejaculatory duct cyst: paramedian, associated with ejaculatory duct obstruction

Prostatitis:

Acute: hypoechoic, enlarged, hyperemic on Doppler, periprostatic fluid
Chronic: heterogeneous, calcifications common, no specific TRUS findings

Prostate abscess:

Hypoechoic or complex fluid collection within the gland
May have internal echoes, debris
TRUS-guided drainage may be performed

Color Doppler

Asymmetric vascularity in the peripheral zone can indicate malignancy. However, Doppler has limited sensitivity and specificity for cancer detection and should not be used as the primary cancer detection tool.

For abscess: hyperemia surrounding the collection; internal vascularity absent (necrotic).

TRUS-Guided Biopsy Basics

If your department performs TRUS-guided biopsies, you may assist or perform the biopsy portion:

Template: Traditional 12-core systematic biopsy samples from base, mid-gland, and apex bilaterally in the PZ. MRI-fusion systems add targeted cores to suspicious lesions.

Needle path: A biopsy guide attaches to the probe. The 18-gauge spring-loaded biopsy needle fires along the guide channel.

Your role: Maintain probe position during needle firing, document core locations, label cores in formalin containers correctly.

Post-biopsy: Patient may experience hematuria, hematospermia (may persist for weeks — warn the patient), and rectal bleeding for a day or two. Fever within 24 hours = possible infection → urgent evaluation.

Reporting

Document:

Prostate volume (three measurements, calculated volume)
Zonal anatomy description
Any focal lesion (location using clock position and zone, size, echogenicity)
Seminal vesicle appearance
Color Doppler findings
If biopsy: number of cores, locations, any complications

Prostate volume calculations are available in SonoBuddy's Calculators tab — use it to quickly calculate volume from your three-axis measurements.

Prostate Ultrasound (TRUS): Protocol, Measurements, and Key Findings