Computed tomography of the prostate

One of the most important advantages of prostate CT is the relatively low operator dependence of the method: the results of an examination performed using a standard method can be reviewed and interpreted by different specialists without the need for a repeat examination.

Advantages of multispiral computed tomography of the prostate:

• high spatial resolution;
• high research speed;
• the possibility of three-dimensional and multi-planar reconstruction of images;
• low operator dependence of the method;
• possibility of standardization of research;
• relatively high availability of equipment (in terms of the number of devices and cost of examination).

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The purpose of performing a computed tomography scan of the prostate

The main purpose of performing CT of the pelvis is to determine the stage of regional spread of prostate cancer (primarily this concerns the detection of metastatic lesions of the lymph nodes).

Indications for computed tomography of the prostate

The main indications for performing MSCT of the pelvic organs:

• detection of regional lymphadenopathy in patients with verified prostate cancer;
• detection of tumor spread to the pelvic organs in patients at high risk of local spread of the oncological process (PSA level >20 ng/ml, Gleason score of 8-10);
• radiation therapy planning.

To identify distant metastases, CT scans of the lungs, brain, liver, and adrenal glands are performed.

Preparation for a CT scan of the prostate

Preparation of patients for MSCT of the pelvic and abdominal organs includes oral contrast of the small and large intestines with a positive or negative substance, which is necessary for accurate differentiation of lymph nodes and intestinal loops. A 3-4% solution of sodium amidotrizoate (urografin) or hypaque (40 ml of contrast agent per 1000 ml of water) is used as a positive contrast agent; it is divided into 2 parts of 500 ml and taken in the evening before the examination, as well as in the morning on the day of the examination. Water can be used as a negative contrast agent (1500 ml 1 hour before the examination), which is especially important when performing MSCT with intravenous contrast and three-dimensional reconstruction of the image.

MSCT of the pelvis is performed with a full bladder. Some researchers suggest filling the rectum with a contrast agent or an inflatable balloon. MSCT of the abdominal organs and retroperitoneal space can be performed at least 3-4 days after X-ray examinations of the digestive tract with barium sulfate due to possible artifacts in CT.

MSCT with intravenous contrast in patients with risk factors for contrast-induced nephropathy (diabetic nephropathy, dehydration, congestive heart failure, age over 70 years) can only be performed after appropriate preparation in the form of intravenous or oral hydration (2.5 liters of fluid within 24 hours before the examination). If possible, the intake of nephrotoxic drugs (non-steroidal anti-inflammatory drugs, dipyridamole, metformin) should be discontinued 48 hours before MSCT with intravenous contrast.

Methodology of prostate computed tomography examination

When performing MSCT, the patient is placed on his back with his arms raised. The examination of the pelvic organs and retroperitoneal space (scanning range - from the diaphragm to the ischial tuberosities) is performed with collimation of the X-ray beam of 0.5-1.5 mm, reconstruction of thin sections of 1.5-3 mm in three planes, viewing tomograms in soft tissue and bone windows.

Intravenous contrast is necessary to clarify the tumor boundaries and identify invasion of surrounding structures. The contrast agent (concentration of 300-370 mg iodine per 1 ml) is administered using an automatic injector in a volume of 100-120 ml at a rate of 3-4 ml/s, followed by the introduction of about 50 ml of physiological solution. The examination of the pelvis begins with a delay of 25-30 s from the start of intravenous administration of the contrast agent, which allows obtaining images in the early arterial phase of contrast. Additionally, the interstitial phase of contrast can be used (delay of 60-70 s), which is more informative for assessing the tumor boundaries.

Contraindications to computed tomography of the prostate

There are no absolute contraindications for prostate CT. Patients with a history of severe allergic reactions to iodine-containing contrast agents are contraindicated to undergo CT with intravenous contrast.

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Interpretation of the results of computed tomography of the prostate

Normal prostate gland

On MSCT, it has a uniform density (sometimes with small calcifications) without zonal differentiation.

The volume of the gland is calculated using the ellipse formula:

V (mm3 ^or ml) = x • y • z • π/6, where x is the transverse dimension; y is the anterior-posterior dimension; z is the vertical dimension; π/6 - 0.5.

Normally, the seminal vesicles have a tubular structure, are symmetrical, up to 5 cm in size, and are separated from the urinary bladder by a layer of fatty tissue, the absence of which serves as a criterion for tumor invasion.

Benign prostatic hyperplasia

An increase in the volume of the prostate gland (more than 20 cm ³ ) is revealed due to the proliferation of nodes in the paraurethral zone, which in some patients is accompanied by intravesical growth. In addition, when performing MSCT with intravenous contrast in the excretory phase (5-7 minutes after the drug is administered), it is possible to detect an elevation of the distal ureters (due to an increase in the volume of the prostate gland), trabecularity of the wall and diverticula of the bladder due to hypertrophy of the muscle that pushes out urine in response to partial obstruction of the urethra. When performing micturition multispiral cystourethrography after filling the bladder with a contrast agent, it is possible to visualize the urethra and identify its strictures.

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Adenocarcinoma of the prostate gland

Foci of adenocarcinoma inside the prostate gland can be identified by active accumulation of contrast agent in the arterial phase (25-30 sec from the moment of intravenous administration). Extraprostatic spread of prostate cancer can be identified by the presence of local bulging, often with an asymmetric enlargement of the seminal vesicle and the disappearance of liquid contents. CT sign of invasion of adjacent organs and structures (bladder, rectum, muscles and walls of the small pelvis) is the lack of differentiation of layers of fatty tissue.

Evaluation of pelvic and retroperitoneal lymph nodes using MSCT is based on determining their quantitative and qualitative changes. The method allows visualizing the most typical areas of their lesion in prostate cancer (obturator, internal and external iliac groups). Obturator lymph nodes belong to the medial chain of the external iliac group; they are located along the lateral wall of the pelvis at the level of the acetabulum. The main CT sign of lymphadenopathy is the size of the lymph nodes. The upper limit of the CT norm is the transverse (smallest) diameter of the lymph node, equal to 15 mm. However, the sensitivity and specificity of CT in detecting lymphadenopathy varies from 20 to 90%, since the method does not allow detecting metastases in non-enlarged lymph nodes and often gives false-negative results.

Analysis of tomograms of the pelvis and retroperitoneal space necessarily includes viewing images in a bone window, which allows identifying hyperdense foci of osteosclerosis corresponding to typical osteoblastic metastases of prostate cancer in the bones of the pelvis, lumbar and thoracic spine, femurs, and ribs.

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Operating characteristics

MSCT does not allow differentiation of zonal anatomy and visualization of the prostate capsule, which limits the capabilities of this method in detecting prostate cancer and determining the local prevalence of the oncoprocess. The high frequency of false-negative MSCT results in staging prostate cancer is due to the fact that stage T3 is established only in the presence of a large tumor with extraprostatic growth and involvement of the seminal vesicle. Detection of stage T3a, especially with limited extracapsular tumor growth, or initial involvement of the seminal vesicles using MSCT is almost impossible. MSCT is not informative enough in assessing the effectiveness of prostate cancer treatment and detecting local relapse.

Complications of Prostate CT Scan

Modern MSCT of the prostate is a virtually safe diagnostic method acceptable for most patients. The development of iodine-containing contrast agents and the emergence of non-ionic agents (iopromide, iogexol) have resulted in a 5-7-fold decrease in the incidence of severe adverse reactions. Due to this, MSCT with intravenous contrast has become an accessible outpatient examination technique. Despite the lower cost of ionic contrast agents compared to non-ionic agents, the latter have become the drugs of choice for MSCT by the end of the 1990s. When using non-ionic contrast agents in cases of moderate allergic reactions in the anamnesis, premedication with prednisolone (30 mg per os 12 and 2 hours before the examination) can be administered.

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Aftercare

Intravenous or oral hydration should be continued for 12-24 hours after the study.

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Prospects for Prostate CT Scanning

Prospects for the development of CT diagnostics of prostate cancer are associated with the use of multi-slice (64-256) tomography, which allows for a study with a slice thickness of about 0.5 mm, isotropic voxels and image reconstruction in any plane. Due to the increase in tomography speed, it will be possible to perform perfusion MSCT of the prostate gland with the detection of foci of tumor neoangiogenesis. Currently, its perfusion is assessed using MRI with intravenous contrast or ultrasound.