Equipment
Transrectal ultrasonography (TRUS) of the prostate has made use of both side-fire and end-fire ultrasound probes. Understanding the differences between them is critical for mastery of TRUS, in that the 2 probe types yield entirely different view points that create confusion if one type is used in the manner that is appropriate for the other. The directions of imaging should be obvious from the names of the probe types, but the full implications for TRUS of the prostate may not be.
Side-fire probes project laterally. Thus, twisting the probe while keeping its axis neutral with respect to the sagittal plane laterally enables lateral visualization.
In contrast, end-fire probes project an imaging plane either directly or at a slight angle from the end of the probe. Thus, to visualize the lateral areas, the probe handle must be angled away from the side of interest, with the anus used as a fulcrum to gain accurate placement. For example, to visualize the right side of the prostate, the handle would be moved downward and toward the patient’s dependent left side.
The most widely used probe for TRUS is a 7-MHz transducer within an endorectal probe. This can produce images in both sagittal and axial planes.
Patient Preparation
Anesthesia
In the past, TRUS was performed without any infiltrative anesthesia. Currently, however, it is a common practice to infiltrate lidocaine into the periprostatic area.
Pareek et al, in a randomized, double-blind, placebo-controlled study using a technique of periprostatic nerve blockade, reported significant pain control during and after biopsy. [34] This technique involved injection of 2.5 mL of lidocaine on each side at the prostate base at the junction of the prostate and the seminal vesicle (using a 5-in, 22-gauge spinal needle through the ultrasound probe).
Alavi et al, in a study comparing the efficacy of intrarectal lidocaine gel with that of periprostatic nerve block, concluded that the nerve block was superior for pain control. [35] With this technique, saturation biopsies including as many as 20 cores could be performed.
Mutaguchi et al reported that local anesthesia with an intraprostatic block provided better pain control for prostate biopsy than the use of a periprostatic block. [36] In the intraprostatic block technique, 10 mL of 1% lidocaine was injected into 2-3 sites of each prostate lobe.
In the periprostatic block technique described by the investigators, 5 mL of 1% lidocaine was injected via a 7-in. 22-gauge spinal needle into the region of the prostatic vascular pedicle just lateral to the junction of seminal vesicles and the prostate. [36] The needle was slowly withdrawn to the prostatic apex, and an additional 5 mL of lidocaine was injected at the apex.
A randomized controlled trial comparing pelvic plexus block to periprostatic nerve block demonstrated better pain control with the former technique. While the procedure is more foreign to urologists, the patients experience less pain and this technique should be considered in men undergoing office prostate biopsy. [37]
Positioning
The left lateral, lithotomy, and knee-elbow positions have all been used for TRUS. If a patient is undergoing TRUS of the prostate with a side-fire probe, the probe should remain essentially in the midline and should be twisted to reach the lateral aspects. Thus, patient positioning is relatively unimportant, as long as the anus is accessible.
Conversely, if a patient is undergoing TRUS of the prostate with an end-fire probe, he must be positioned so that the ultrasound probe handle can be dropped far enough to reach beneath the plane of the examination table when the right lateral border of the prostate is being visualized. This is most readily accomplished if the patient’s buttocks are directly over the corner of the table, with his legs flexed toward his chest and held by the table extension.
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Transverse image of the prostate showing a hypertrophied transition zone (yellow arrows) and a compressed peripheral zone (blue arrows).
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Large hypoechoic area along the left peripheral zone, suggestive of carcinoma.
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Sagittal image of the prostate showing a hypoechoic area (white arrow). This area was a focus of cancer on biopsy findings.
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A large hypoechoic area in the left peripheral zone suggestive of prostate cancer.
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Axial and sagittal images of the prostate showing extensive hypoechoic areas. This patient had a prostate-specific antigen level of 17 ng/mL and digital rectal examination findings highly suggestive of cancer. Biopsy revealed granulomatous prostatitis.
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Axial image of a prostate. White arrows show the asymmetrical anterior prostate. This could only be appreciated on TRUS images.
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Sagittal image of a prostate. White arrows show darkly hypoechoic areas suggestive of periprostatic veins.
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Axial images of the seminal vesicles. White arrows indicate the ampulla of the vas deferens.
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Sagittal image of the prostate. White arrows indicate calcification in the prostatic urethra.
Tables
Table 1. PI-RADS Assessment Categories |
|
Assessment categories |
Likelihood for cancer |
PI-RADS1 |
Very low |
PI-RADS2 |
Low |
PI-RADS3 |
Intermediate |
PI-RADS4 |
High |
P-IRADS5 |
Very high |
