Instrumental methods of renal examination

Ultrasound imaging: US and Doppler

Ultrasound examination is a basic non-invasive tool. Using it, the physician determines the location, contours, and size of the kidneys, assesses the condition of the pelvicalyceal system (PCS), and detects mass lesions (tumors, cysts, abscesses) or calculi.

Specific ultrasound signs of chronic kidney disease (CKD) include increased echogenicity of the cortical layer and loss of corticomedullary differentiation—the disappearance of the clear boundary between the cortex and medulla.

Doppler ultrasound is used to analyze renal blood flow in both major and intrarenal vessels. An important parameter here is the resistive index (the ratio of peak systolic to diastolic velocity). Its increase is characteristic of acute kidney injury (AKI) or transplant rejection. This method is also indispensable for detecting renal artery stenosis (manifested by weakened intrarenal blood flow) and venous thrombosis.

Radiological methods and tomography

Plain radiography has limited value: in asthenic individuals, it allows the visualization of kidney contours, but it is more commonly used to search for radiopaque stones. Much more informative is intravenous (excretory) urography—the injection of a contrast agent followed by a series of images. This is the "gold standard" when urolithiasis is suspected.

The urography protocol includes a plain radiograph, a 5-minute image (nephrographic phase — parenchyma is visible), and images at 20 and 45 minutes (assessment of excretory function and ureteral patency). In cases of renal blockade or decreased function, delayed images are taken after 6–12 hours.

Normally, the kidneys lie at the level of Th11–L3, with the right kidney lower than the left. The thickness of the parenchyma at the poles (3–4 cm) is greater than in the center (2.5 cm). If the reverse pattern (thinning at the poles) is observed in chronic pyelonephritis, this is called Hodson's sign.

Computed tomography (CT) is the priority method for diagnosing renal mass lesions, as it provides a more detailed picture of the retroperitoneal space and adrenal glands. Magnetic resonance imaging (MRI) and MR angiography are actively developing as high-precision alternatives.

Angiography and vascular assessment

Invasive contrast methods (angiography) involve vascular catheterization.

• Arteriography: contrast is injected selectively into the renal artery. Indicated when renovascular hypertension (stenosis) is suspected, for diagnosis and embolization in bleeding, and for tumors when CT cannot be performed. A huge advantage of arteriography is its therapeutic potential: the ability to immediately perform balloon dilation and stenting of the narrowed segment. The main risk of the procedure is cholesterol embolization in patients with atherosclerosis.
• Venography: performed by passing a catheter from the femoral vein through the inferior vena cava to the renal veins. The main goal is to confirm renal vein thrombosis.

It is important to remember the risks of using contrast agents. Allergic reactions and contrast-induced nephropathy are possible, the risk of which increases manifold in diabetes mellitus, multiple myeloma, and pre-existing renal pathology. To prevent complications, one must avoid dehydration, carefully use diuretics, and meticulously select the type of agent.

Radionuclide diagnostics

The methods are based on the ability of renal tissue to take up and excrete administered radiopharmaceuticals. The process is recorded by a gamma camera. The main value is the ability to assess the split function of each kidney, which cannot be done with a routine blood test.

• Diagnosis of arterial stenosis: when a vessel is narrowed, the radiopharmaceutical accumulates longer, peak activity is delayed, and excretion is slowed down. To detect hidden perfusion abnormalities, captopril renography is used—an ACE inhibitor relieves the spasm of the efferent arteriole, revealing the hemodynamic problem.
• Diagnosis of obstruction: if the radionuclide is retained in the renal pelvis, a diuretic test is performed. In the presence of a mechanical obstacle, the administration of diuretics does not accelerate the excretion of the drug.
• Cortex visualization: has high sensitivity for detecting early nephrosclerosis.

Morphological diagnostics (Biopsy)

Percutaneous puncture (less often semi-open) biopsy is necessary for precise histological verification. Main indications: selecting therapy by clarifying the type of glomerulonephritis and diagnosing amyloidosis (although amyloid can also be sought in the gums or rectal mucosa).

The procedure is strictly contraindicated in:

1. Hemostatic disorders (thrombocytopenia, anticoagulant therapy, bleeding diathesis).
2. Inability to communicate with the patient (psychosis, coma).
3. Severe uncontrolled arterial hypertension.
4. Presence of only a single functioning kidney.
5. Shrunken kidneys.

Class and exam questions

What else to study on this topic

• Laboratory markers of immuno-inflammatory activity (ANCA, ANA, antibodies)
• Blood electrolyte changes in CKD staging
• Specific laboratory diagnostics of lupus nephritis and Goodpasture syndrome
• Cryoglobulins and their association with virus-associated glomerulonephritides
• Prevention of contrast-induced nephropathy

Other topics in the "Urinary System" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.