Technique

Patient preparation

TRUS can safely be performed as an office procedure. Some institutions advocate the routine use of a pre-procedure cleansing enema to decrease rectal content. TRUS is contraindicated in the presence of a UTI and patients on anticoagulants must be advised to stop therapy for 2-3 days. Given the high incidence of transient post-TRUS bacteraemia (up to 73%) and risk of sepsis, all patients must be given prophylactic antibiotics. Protocols may vary according to local policy, but a broad-spectrum antibiotic (e.g., three oral doses of a quinolone or a single dose of IV gen-tamicin) will usually suffice, but high-risk patients (e.g., valvular heart disease) must receive a penicillin-based antibiotic as well. The procedure can be performed with the patient in the lateral decubitus, lithotomy, or knee-chest position. A careful digital examination to assess anal tone, rectal contents, and prostatic morphology is mandatory.

Equipment

Most procedures are performed using a 6-7.5-MHz transrectal US transducer which can scan in the transverse as well as the longitudinal/sagittal plane. Transverse images better demonstrate prostatic symmetry and lateral capsular anatomy. The longitudinal is used for biopsies due to the easier visualisation of the prostate base and apex. A spring-loaded Tru-Cut type 18 G biopsy gun is used for prostate biopsy.

Anesthesia

Traditionally, six-core sextant biopsies were usually performed without anesthesia. More recently however, the discomfort associated with the general trends toward increased biopsy core numbers has resulted in greater use of local anesthesia. Various methods have been described, including—

• Peri-prostatic nerve blockade provides the best anesthesia (10 mL of 1% lidocaine)

• Intra-rectal 2% lidocaine jelly

• Entonox gas inhalation

• Oral anti-inflammatories

Interpretation

A real-time interpretation by an experienced physician provides greatest yield from a TRUS examination. A systematic approach is vital.

FIGURE 6.1. Zonal anatomy of the prostate gland—(A) sagittal and (B) transverse view (with permission from Campbell's Urology, Saunders, 2000, 3044-3045) (TZ = transitional zone, CZ = central zone, PZ = peripheral zone, U = urethra, EJD = ejaculatory ducts, AFS = anterior fibromuscular stroma)

Prostate zones (see Fig 6.1)

BPH is limited to the transitional zone (TZ) of the prostate which lies anteriorly. The increasing size of the TZ usually appears hypoechoic and compresses the more posteriorly placed central (CZ) and peripheral zones (PZ). While it is relatively easy to distinguish the TZ from the PZ, the CZ is not easy identified on TRUSS.

Prostate cancer

TRUS detects 50% more patients with CAP than DRE in asymptomatic patients. The appearance of CAP on TRUS is a hetero-genous phenomenon. Cancers usually arise within the PZ, but up to 20% can be located in the TZ. The classic hypoechoic area in the PZ is not always seen and many cancers are isoechoic and only detectable from systematic biopsies. Suspicious palpable nodules on rectal examination are more likely to appear as hypoechoic lesions. Generally, up to 70% of tumors are hypoechoic, while the rest are indistinguishable from surrounding prostatic tissue (isoechoic). TZ cancers are more likely to be isoechoic. There appears to be no relationship between the tumor echogenicity and the subsequent Gleason score. Prostatic inflammation, infarcts, atrophy, and hypertrophy can also result in the appearance of hypoechoic lesions.

Capsule

The normal prostate capsule is a symmetrical and well-defined, continuous structure which appears hyperechoic. Breaches or distortion of the capsule (e.g., secondary to local tumor extension) can usually be demonstrated on TRUSS.

Cysts

These can be seen as well-defined, smooth, spherical structures which are echo-poor and cast an acoustic shadow beyond the lesion. Puncture of these lesions with the biopsy gun will often result in obvious resolution.

Calcification

Calcification is frequently seen in the interface between the TZ and PZ and usually is a feature of BPH. Calcification can also be associated with prostatitis and prostatic malignancies, although this is generally regarded as a non-specific finding.

Seminal vesicles and ejaculatory ducts

The seminal vesicles (SV) can easily be seen on the posterior surface of the bladder, just superior to the prostate. Although usually symmetrical in appearance, asymmetry is a common non-diagnostic finding. Other causes of asymmetry or SV dilatation include ejaculatory duct obstruction and invasion by CAP. An A-P diameter >15 mm and a length >35 mm is typical of SV obstruction. The SV may be absent or atrophic in patients with congenital absence of the vas. TRUS-aided SV aspiration can help detect increased sperm concentration in the SV, which is suggestive of an obstructive pathology.

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