Transrectal Prostate Ultrasound
Transrectal ultrasound (TRUS) images the prostate, seminal vesicles, periprostatic tissue and the rectal wall with a high frequency (6 to 12 MHz) end fire or biplane endorectal probe. The patient lies in the left lateral position with the knees flexed.
The probe, covered by a sheath and lubricating gel, is passed into the rectum, and the gland is scanned in transverse and sagittal planes from the base to the apex. Prostate volume is calculated by the ellipsoid formula (length x width x height x 0.52). Colour and power Doppler show vascularity, and elastography or contrast enhanced ultrasound may add information on stiffness and perfusion.
The examination takes 10 to 20 minutes. Its commonest use today is to direct systematic or targeted biopsy, often fused with prior multiparametric MR images, and to measure gland volume before treatment.
Prostate cancer is the commonest cancer in men in many countries, and benign prostatic enlargement affects more than half of men over 60 years. TRUS alone cannot reliably separate cancer from benign tissue: up to 40% of cancers are isoechoic, and only 20 to 30% of hypoechoic peripheral zone lesions are malignant. Its value lies in measuring volume, directing tissue sampling, and detecting complications and abscess.
Indications. Elevated or rising prostate specific antigen, or abnormal digital rectal examination, for biopsy. Measurement of gland volume and prostate specific antigen density. Planning of surgery for benign enlargement or of brachytherapy. Ultrasound control of focal therapy and of seed placement. Suspected prostatic abscess, cysts, utricle or ejaculatory duct cysts and stones.
Male infertility with low volume or azoospermic semen (seminal vesicle and ejaculatory duct obstruction, absent vas deferens). Haemospermia of uncertain cause. Staging of local extension in selected cases (limited accuracy; MR is preferred). Follow up after radiotherapy or ablation.
Contraindications and precautions. Acute prostatitis or active urinary tract infection (relative; abscess is an exception when drainage is intended), anal stenosis, painful anal fissure or rectal surgery (consider transperineal route), bleeding disorders and anticoagulant use (the plan is made with the prescribing doctor and the local rule), and prosthetic heart valve or immunosuppression (prophylactic antibiotics).
Latex allergy needs a latex free sheath. A urine dipstick is checked before biopsy. Prophylactic antibiotic is given before biopsy, with a single dose of a fluoroquinolone sparing regimen where resistance is common. A rectal enema may be used to clear faeces.
Informed consent covers pain, bleeding (haematuria, haemospermia, rectal bleeding), infection (up to 1 to 3% sepsis, higher where fluoroquinolone resistant bowel flora are common), urinary retention (under 1%) and erectile effects.
Preparation and technique. The bladder should be partly full for volume views. A digital rectal examination is done first. The probe is inserted gently and the gland is scanned from the seminal vesicles to the apex.
Zones are identified: peripheral zone (70% of the gland, the main site of cancer), transition zone (enlarges in benign hyperplasia), central zone and anterior fibromuscular stroma.
For biopsy, a periprostatic nerve block with local anaesthetic reduces pain, and 10 to 12 cores are taken systematically from the peripheral zone (laterally directed cores from base, mid-gland and apex on each side), with extra targeted cores from suspicious MR or ultrasound lesions. The transperineal route has a lower infection rate and better access to the anterior zone and apex.
