Transrectal ultrasound (TRUSI)

Transrectal ultrasound examination (TRUS) is currently considered the main method for recognizing prostate diseases. Transrectal sensors operate at frequencies of 6 MHz and higher, which ensures high image quality and allows for detailed visualization of the structure of the prostate gland and surrounding organs and tissues. The transrectal sensor is compact, has a working part length of 12-15 cm and a diameter of up to 1.5 cm.

According to various authors, TRUS provides more accurate and detailed information about the condition of the prostate; visualization of the entire volume of the prostate and its capsule with good image quality, the best conditions for accurate measurement of its size, the possibility of performing ultrasound micturition cystourethroscopy, which makes this method mandatory in prostate examination.

The only drawback of the technique is the limitation of its use in certain diseases of the rectum and after perineal surgery.

Transrectal sensors are divided into three types: those operating in one plane; biplane, having two transducers (allowing to obtain an image of the prostate in the transverse and longitudinal planes); multiplane - with the ability to change the scanning plane by 180°.

Indications for transrectal examination of the prostate

Clinicians identify the following indications for TRUS:

• elevated levels of prostate-specific antigen (PSA), detection of prostate cancer;
• assessment of the volume of brachytherapy before its start;
• brachytherapy direction;
• tumor, palpable formation, enlargement of the prostate gland during physical examination (per rectum);
• determination of the site of prostate biopsy;
• infertility, diagnosis of obstruction or cyst of the spermatic cord;
• hematospermia, detection of stones;
• abscess, prostatitis, infectious lesion;
• difficulty urinating (infravesical obstruction);
• evaluation of therapy effectiveness.

Preparation for TRUS

Before TRUS, the patient must be explained the procedure technique and warned about possible discomfort. It is recommended to give the patient a cleansing enema before the examination, but this is not necessary for a diagnostic examination. In cases of planned transrectal biopsy, careful preparation of the rectum is necessary. A mandatory condition for transrectal ultrasound examination is sufficient filling of the bladder (150-200 cm ³ ), providing conditions for examining its walls.

During the examination, the patient lies on his left side with his knees drawn up to his stomach. The depth of insertion of the sensor should not exceed 15-20 cm, which minimizes the risk of rectal injury. If necessary, the examination can be performed in a lying position on the right side or on the back with the knees apart. The latter position is used when performing a prostate biopsy using perineal access.

How is TRUS performed?

It is recommended to start transrectal ultrasound examination with an image in the transverse plane. This allows for a quick assessment of the general condition of the prostate gland. At the first stage, the sensor is inserted into the rectum to the level of the seminal vesicles and the bottom of the bladder. By moving the sensor back approximately 0.5 cm, the most complete cross-section of the prostate gland is obtained. Changing the operating frequency of the sensor in the range from 6 to 12 MHz allows for adjusting the depth of penetration of ultrasound waves and obtaining not only an image of the smallest structures of the prostate gland, but also assessing the condition of surrounding organs and tissues.

Just like with TAUSI, TRUS evaluates the following quantitative and qualitative characteristics of the prostate gland:

• type of prostate growth;
• the degree of prostate invasion into the bladder;
• prostate shape;
• prostate symmetry;
• dimensions (width, thickness, length) and volume of the prostate;
• volume of the middle lobe (if any);
• volume of hyperplastic prostate tissue;
• echostructure of the prostate.

It should be noted that for assessing the type of growth, shape, degree of invasion into the bladder and symmetry of the prostate, TAUSI has an advantage over TRUS, due to the large angle of the prostate gland scanning zone and the ability to display the entire prostate on the ultrasound monitor. This is especially important when examining large prostates (more than 80 cm ³ ). Unlike TAUSI, there are significantly fewer reasons for insufficient visualization of the prostate with TRUS.

• Pronounced intravesical and mixed growth forms with a middle lobe (the intravesical part of the prostate is not determined).
• A decrease in bladder capacity to less than 60 ml in patients with intravesical and mixed forms of prostate growth with a middle lobe.

The hyperplastic prostate gland is defined on echograms as a homogeneous formation, varying in shape and size, but always with clear, even contours and a well-defined capsule. Hyperplastic prostate tissue can develop unevenly and create asymmetry during frontal echoscanning.

When assessing the echostructure of the hyperplastic prostate gland using TRUS, it should be noted that this method is highly informative. The following changes in the echodensity of the prostate were revealed:

• hyperechoic areas with a clear acoustic path (stones);
• hyperechoic areas without an acoustic path (areas of sclerotically altered tissue);
• anechoic areas (cysts);
• decreased echo density of the prostate gland,
• increased echo density of the prostate;
• heterogeneity of the echostructure of the prostate due to the combination of areas of increased and decreased echo density;
• visualization of adenomatous nodes and their clear differentiation from unchanged prostate tissue.

The difference in measuring the size and volume of the prostate between TAUSI and TRUS is small and averages 5.1%. It should be noted that the thickness of the prostate differs the most, which is explained by the not always correct choice of the angle of transverse scanning of the prostate gland with an abdominal sensor (a slightly oblique cut is obtained, which leads to an increase in its diameter). However, there is a tendency to reduce the volume of the prostate calculated with TRUS in relation to TAUSI. This is due to better visualization of the prostate capsule and, accordingly, a more accurate determination of its measurement points.

It should be noted that no significant difference was found when comparing the results of prostate measurements using different ultrasound machines. On average, they were 0.32 ± 0.04 cm for width, 0.39 ± 0.07 cm for thickness, and 0.45 ± 0.08 cm for prostate length. However, the prostate sizes of the same patient measured by different researchers were more different. They were on average 0.68 ± 0.08 cm for width, 0.74 ± 0.12 cm for thickness, and 0.69 ± 0.09 cm for prostate length. Such results can be explained by the fact that each ultrasound specialist has his or her own preferences in choosing measurement points and prostate scanning angles, which is especially noticeable when measuring thickness (anterior-posterior size).