Ultrasound of kidneys and ureters

Where to do an ultrasound of the kidneys and how to properly prepare for this study, we will consider these issues in more detail. Ultrasound examination of the kidneys refers to the complex of diagnostics of the urinary system and is considered an effective and safe method for detecting pathologies. The procedure itself is minimally invasive and provides complete information about the size, shape and location of the kidneys. Ultrasound waves visualize the kidney, thanks to which it is possible to assess the blood supply and structure of the organ.

To perform the procedure, the patient lies on the couch on his side, a special gel is applied to the skin and an examination is carried out using a sensor. The main indications for ultrasound of the kidneys are: infectious and inflammatory diseases, preventive examinations and monitoring of organs after illnesses or surgery. Diseases of the endocrine system, changes in kidney function, abnormal urine tests, lumbar pain and many other symptoms are indications for ultrasound.

Indications for ultrasound of the kidneys and ureters

1. Pain in the kidneys or along the ureters.
2. Suspected renal tumor (large kidney).
3. A non-functioning kidney, according to urography.
4. Hematuria.

Indications for ultrasound of the kidneys and ureters

Preparation for ultrasound of the kidneys and ureters

1. Patient preparation. No preparation is required. If a bladder examination is required, the patient should drink water.
2. Patient position. Begin the examination with the patient lying on his back. Apply the gel randomly to the upper right abdomen.
3. Selecting a sensor: Use a 3.5 MHz sensor for adults, a 5 MHz sensor for children and thin adults.
4. Setting the required sensitivity level. Begin the examination by placing the transducer in the right upper abdomen. Tilt the transducer and adjust the sensitivity to obtain an optimal image of the renal parenchyma.

Preparation for ultrasound of the kidneys and ureters

Ultrasound of any organ should be multi-positional, i.e. scanning should be performed from all surfaces accessible for ultrasound visualization.

The examination of the kidneys begins with the lumbar region, scanning them from behind in the longitudinal direction. Then the sensor is moved to the lateral and anterior surface of the abdominal wall. After this, a series of transverse and oblique sections are made in the same sections, determining the topography, size, condition of the parenchyma, renal sinus and the calyceal-pelvic system (CPS).

In this case, attention is paid to the contour of the renal parenchyma, its thickness, homogeneity, the presence or absence of visualization of the renal pelvis and calyceal system and pathological formations, the size of the renal sinus, as well as the mobility of the kidney during breathing.

The right kidney is visualized with the patient in a supine position, using the liver as an acoustic window.

Scanning is always done with a deep breath hold: ask the patient to take a deep breath and hold it. Remember to tell the patient to relax and breathe normally afterwards.

Methodology for performing ultrasound examination of the kidneys and ureters

A normal kidney in longitudinal sections is a bean-shaped formation with a clear, even outer contour created by a fibrous capsule in the form of a thin (up to 1.5 mm) hyperechoic layer of tissue between the paranephrium and the parenchyma. The renal parenchyma is a tissue of uniform echostructure and usually of reduced echodensity (hypoechoic). Normally, its thickness is about 1.5-2.0 cm. Its inner part borders the renal sinus and has a slightly uneven contour due to the papillae protruding into the sinus. Sometimes, especially in young people, triangular pyramids are visible in the renal parenchyma, with their base facing the outer contour of the kidney and their apex facing the sinus, forming papillae. The pyramids have an even lower echodensity than the parenchyma. The echogenicity of the renal sinus is similar to that of the paranephric tissue. It is located in the center of the kidney and is surrounded by parenchyma during longitudinal echoscanning. During echography of a normal kidney, only some vascular bundles can be visualized in it. The calyceal-pelvic system is not normally determined. When examining patients with a water load or with a full bladder, the pelvis is visualized as an anechoic formation. Its anteroposterior size should not exceed 1.0-1.5 cm. Renal vessels are usually visible during transverse or oblique scanning from the anterior abdominal wall.

Normally, during breathing, the mobility of the kidney is 2-3 cm. The paranephric tissue has a homogeneous echostructure, increased echogenicity compared to renal tissue; does not have pathological formations.

Ultrasound is of great importance in the differential diagnosis of volumetric renal lesions. In this case, a tumor originating from the renal parenchyma is defined as a round or oval formation, varying in echo density. According to this feature, all tumors can be divided into two large groups: solid (dense) and liquid. The echo structure can be homogeneous and heterogeneous. Depending on the growth form and localization, the tumor can be extrarenal (changes the size and contour of the kidney), intrarenal (located in the sinus, deforming it) or mixed. With a large tumor occupying the entire kidney, the renal sinus may not be determined. With displacement and compression of the calyceal-pelvic system, its dilation is possible.

The diagnostic accuracy of ultrasound for kidney neoplasms reaches 97.3%.

When a volumetric formation in the kidney is detected during an examination, its nature (dense or liquid) is first determined.

Measurements taken during ultrasound examination generally have lower values than the same parameters obtained during radiography: they are more accurate.

Both kidneys should be approximately the same size in adults; a difference in kidney length of more than 2 cm is pathological.

Ultrasound signs of normal kidney and ureters

If any kidney is not visualized, repeat the examination. Adjust sensitivity for clear visualization of the liver and spleen parenchyma and scan in different projections. Determine the size of the visualized kidney. Renal hypertrophy occurs (at any age) several months after the removal of the other kidney or its cessation of functioning. If there is only one large kidney, and the second is not detected even with the most careful search, then it is possible that the patient has only one kidney.

Of all dense (echo-positive) neoplasms of the kidney, the most common is renal cell carcinoma (according to different authors, from 85 to 96%). Benign tumors (oncocytoma, angiomyolipoma, adenoma, leiomyoma, etc.) make up 5 to 9%.

It should be emphasized that it is impossible to judge the morphological structure of a tumor based on non-morphological research methods, which include ultrasound.

When a dense (solid) kidney formation is detected, the echogenicity of which may be lower, higher or close to the latter, attention is paid to its contours and homogeneity. Thus, in kidney cancer, a formation of non-uniform echostructure with alternating areas of reduced and increased echodensity is detected. Often, such formations contain echo-negative (liquid) inclusions caused by hemorrhages and necrosis. Echograms reveal the absence of the effect of amplification of reflected ultrasound waves (in contrast to liquid formations) or their weakening at the distal border of the tumor and underlying tissues. The outer contour of a multinodular formation is usually uneven, and in the case of invasion into adjacent tissues, it is unclear. However, it should be borne in mind that a similar echostructure is determined in xanthogranulomatous pyelonephritis, benign kidney tumors and fibrous-cavernous tuberculosis.

Of all solid benign kidney tumors, angiomyolipoma and lipoma have the most characteristic ultrasound picture, which on echograms look like homogeneous formations of increased echogenicity, similar in this feature to paranephric (fatty) tissue. However, more accurate methods used for differential diagnosis of solid kidney formations detected by ultrasound are computed tomography (CT) and MRI.

When an anechoic formation is detected in the kidney, attention is also paid to the homogeneity of its echostructure. A cyst is characterized by homogeneous anechoic contents, smooth contours, absence of internal structures, and amplification of reflected ultrasound waves at the distal border. Internal structures in the liquid medium of the formation may indicate a malignant process (sarcoma, cystic kidney cancer, tumor in the cyst) or such pathological conditions as hematoma, echinococcosis, kidney abscess, tuberculous cavern.

If there is any doubt about the solid or liquid nature of the formation, CT with contrast, MRI or ultrasound-guided puncture with subsequent cytological examination of the obtained fluid and cystography are performed to clarify the diagnosis. If no fluid is obtained during the puncture, then the solid structure of the formation can be assumed and its biopsy can be performed.

Quite often, especially if small, the neoplasm is practically no different in its acoustic properties from normal parenchyma. That is why the closest attention during ultrasound should be paid to irregularities of the kidney contour, deformations of the renal sinus, and thickening of the parenchyma. The minimum size of a renal parenchyma tumor that can be reliably detected during echography is 2 cm. With small formations, differential diagnostics with an additional lobe of the renal parenchyma is often necessary (especially with a "humpbacked" kidney). If ultrasound shows a suspicion of such a formation, then multispiral CT (MSCT) with contrast is used to clarify the diagnosis, the information content of which is significantly higher (especially with small formations) and approaches 100%.

Along with tumor detection, echography provides valuable information about the spread of the process. In addition to signs of germination into neighboring organs, it is possible to diagnose tumor thrombosis of the renal and inferior vena cava, enlarged regional lymph nodes located paraaortically, paracavally and in the artocaval space, but CT and MRI are considered more informative methods for determining the stage of the disease.

With the introduction of ultrasound in medicine, the frequency of detection of kidney cancer (especially asymptomatic forms) has increased significantly. This is due to the use of this method as a screening test during preventive examinations of the population. Asymptomatic course of kidney cancer and its accidental detection using ultrasound are noted in more than 54% of patients.

Ultrasound diagnostics of papillary tumors of the upper urinary tract is extremely difficult. If the papillary tumor of the renal pelvis is small and does not interfere with the outflow of urine from the calyceal-pelvic system, the echographic picture of the kidney may not differ from normal. Tumors of the calyceal-pelvic system appear mainly as hypoechoic formations of irregular shape in the renal sinus. They can easily be mistaken for an enlarged calyx or a cyst of the renal sinus.

Sometimes it is possible to detect and differentiate such a tumor only against the background of expansion of the renal pelvis (with a violation of the outflow of urine) or with the help of artificially created polyuria.

If a tumor of the renal pelvis and calyces infiltrates the renal pedicle or grows into the organ tissue, then its detection with a conventional ultrasound is simplified, but in this situation it is necessary to differentiate it from a tumor of the renal parenchyma.

The ureter is not determined by conventional ultrasound. Only with significant expansion is its partial visualization in the upper and lower third possible. Consequently, diagnostics of papillary formations of the ureter using conventional non-invasive ultrasound is impossible. A new invasive method developed in recent years - endoluminal echography - allows obtaining a high-quality image of the UUT along its entire length and diagnosing any disturbances in its structure (including tumors) with high accuracy. The essence of the method consists in conducting a miniature ultrasound sensor, mounted in a flexible probe, retrogradely along the urinary tract. In addition to detecting the tumor and determining the nature of its growth, this method allows determining the prevalence and degree of tumor invasion into the wall of the urinary tract and surrounding tissues, which is of great importance in determining the stage of the disease.

Ultrasound plays an important role in the comprehensive diagnostics of inflammatory processes in the urinary tract. Thus, in acute pyelonephritis, the presence or absence of visualization of the renal pelvis and calyces system determines the nature of pyelonephritis (obstructive or non-obstructive). Ultrasound also allows detecting edema of the paranephric tissue, which manifests itself not only by limiting the respiratory mobility of the affected kidney, but also by a kind of rarefaction halo around it. Renal carbuncle is a formation of reduced echo density with clear and not always smooth contours. Its internal structure may be heterogeneous, sometimes with small echo-positive inclusions. With purulent contents, the formation will be almost anechoic. At the location of the carbuncle, the kidney contour may be uneven and bulge. Its echographic picture should be differentiated from that of a tuberculous cavern. The latter has a dense echo-positive capsule and denser internal inclusions - calcifications (up to petrifications), which look like hyperechoic formations with a clear acoustic path.

In the initial stages of chronic pyelonephritis, ultrasound does not reveal any reliable signs of the disease. In advanced inflammatory processes resulting in kidney shrinkage, a significant decrease in its size is observed with a relative increase in the area of the renal sinus structures in relation to the parenchyma. The latter acquires a heterogeneous structure, uneven contours and a thickened capsule.

In the final stages of inflammation (pyonephrosis), one can detect an enlarged kidney, thickened capsule, compacted surrounding paranephric tissue, often limited mobility of the affected kidney, decreased parenchyma thickness with expansion and uneven contours of the cups and pelvis, the walls of which, due to cicatricial changes, acquire increased echogenicity. In their lumen, one can visualize a heterogeneous suspension (pus and necrotic tissue) and echo-positive formations with an acoustic shadow (calculi).

Ultrasound is of great help in diagnosing paranephric abscess and purulent changes in the retroperitoneal tissue. Usually, the abscess is located in close proximity to the kidney and looks like an echo-negative oval-shaped formation, almost completely devoid of internal structures. It usually has a clear external and internal contour. Purulent changes in the retroperitoneal tissue are less often encapsulated and more often resemble phlegmon. At the same time, ultrasound allows you to see the fuzzy contours of the muscles and the heterogeneous hypoechoic contents between them and in the retroperitoneal space.

With ultrasound, visualization of a kidney calculus larger than 0.5 cm does not present significant difficulties. A single stone on echograms is defined as a clearly defined, echo-positive (hyperechoic) formation located in the sinus with an acoustic track (shadow) distal to the calculus. Its presence is associated with the complete reflection of ultrasound rays from dense stone structures at the interface. Certain difficulties arise when surrounded by small and flat stones. Under experimental conditions, the minimum thickness of a kidney stone detected by echography is about 1.5 mm. Stones are most clearly visualized with dilation of the renal pelvis and calyces. Small hyperechoic areas of the renal sinus without an acoustic effect can be mistakenly interpreted as stones (cause of overdiagnosis).

Using ultrasound, it is possible to detect any stones, regardless of their chemical composition. That is why metol is used for differential diagnostics of urate lithiasis and papillary neoplasms, when it is necessary to exclude the presence of a radiolucent stone in the kidney when a filling defect in the calyceal-pelvic system is detected on urograms.

Non-invasive echography methods allow to detect stones in the calyces, pelvis, upper third (with its dilation) and intramural part of the ureter with a sufficiently full bladder. Stones in the middle and lower third of the ureter cannot be detected by non-invasive echography. This is due to the presence of gas in the intestine, which prevents the passage of ultrasound waves. Only in rare observations in the absence of gas in the intestine and a significantly dilated ureter is it possible to visualize it fragmentarily in all sections. Detection of a stone in any section of the urinary tract is possible using endoluminal echography if there is a way to pass an ultrasound probe between the stone and the wall of the ureter.

Ultrasound signs of kidney and ureter pathology

The use of ultrasound has significantly simplified the task of differential diagnostics of renal colic and acute processes in the abdominal cavity, as well as gynecological and neurological diseases. Thus, before the introduction of ultrasound diagnostic methods into widespread practice, the examination in the emergency department of hospitals was carried out according to the following scheme: plain radiography and excretory urography, chromocystoscopy, often - blockade of the round ligament of the uterus or spermatic cord. Currently, ultrasound is used to detect impaired urine outflow from the kidneys. If dilation of the renal pelvis and calyces is not detected during the examination of the kidneys, then the pain in the lumbar region of the patient is not associated with impaired urine outflow from the upper urinary tract. However, it should not be forgotten that in the absence of dilation, the renal genesis of pain and the presence of a urological disease cannot be completely excluded. Pain similar to renal colic is observed in thrombosis of the renal vessels, acute non-obstructive inflammatory diseases of the kidneys and urinary tract, etc.

Modern ultrasound diagnostics has a functional focus. Pharmacoechography is considered to be a method that allows assessing the functional state of the UMP. To perform it, after the initial examination of the kidneys and determination of the initial sizes of the calyces and pelvises, 10 mg of furosemide is administered intravenously. After which the examination and measurement of the calyces and pelvises is repeated every 5 minutes. Polyuria can lead to dilation of the calyceal-pelvic system, the degree of which is assessed by measurements. The study is repeated until its size returns to the original. Under normal conditions, dilation is not pronounced and is present for no more than 10 minutes. Its longer persistence (after the introduction of a saluretic during pharmacoechography) indicates the presence of an obstruction to the outflow of urine and / or functional failure of the proximal urinary tract.

You can do an ultrasound of the kidneys in almost any medical institution that has an ultrasound diagnostic device. Often, the procedure is carried out as prescribed by a doctor if there is a suspicion of pathologies and disorders in the functioning of the kidneys.