Norm of Kidney Ultrasonography (Kidney Echography, Kidney Ultrasound)
Bilateral kidneys are properly located and are of normal size and shape. The outer contour is smooth. The kidney is surrounded by echoes reflected from perirenal fat. Intense echoes are reflected by the renal sinus. Absence of calculi, cyst, hydronephrosis, obstruction, or tumor.
Usage of Kidney Ultrasonography (Kidney Echography, Kidney Ultrasound)
Alternative to renal dye imaging tests for clients with allergy to radiographic dyes. Used for detection of hydronephrosis; diagnosis and localization of renal cysts, tumors, or calculi; evaluation of status after renal transplantation; and guidance for antegrade pyelography, biopsy, aspiration, or nephrostomy tube insertion. Also used to screen for preanal hydronephrosis. Although this procedure is inferior to intravenous pyelography when used alone, its advantages include the ability to detect some stones without the use of ionizing radiation. Disadvantages include risk of inaccurate measurement of calculus diameter, poor differentiation of true obstruction from nonobstructed dilatation, and inability to demonstrate the ureteral jet phenomenon at the uterovesical junction.
Description of Kidney Ultrasonography (Kidney Echography, Kidney Ultrasound)
Evaluation of the kidney structure by the creation of an oscilloscopic picture from the echoes of high-frequency sound waves passing over the flank area (acoustic imaging). The time required for the ultrasonic beam to be reflected back to the transducer from differing densities of tissue is converted by a computer to an electrical impulse displayed on an oscilloscopic screen to create a three-dimensional picture of the kidney. The kidney is imaged by use of the liver or spleen as an acoustic window. Renal cysts appear smooth, sonolucent, and spherical, with well-defined borders. In contrast, solid masses are of irregular shape with poorly defined borders and higher attenuation. Inflammatory cysts have thicker walls, have less well-defined borders, and contain low-level echoes. Early hematomas look like cysts and become more echogenic over time. Hydronephrosis is demonstrated by a large extrarenal pelvis, with renal parenchyma not detectable. In multicystic disease, the kidney is smaller than normal size, and the renal pelvis cannot be visualized. In polycystic disease, irregularly shaped cysts >1 mm in diameter are present in variable shapes and sizes. Because ultrasound cannot pinpoint obstruction, the presence of hydronephrosis requires additional confirmatory testing such as computed tomography, intravenous pyelography, or magnetic resonance urography.
Professional Considerations of Kidney Ultrasonography (Kidney Echography, Kidney Ultrasound)
Consent form NOT required.
- The client must be hydrated before the procedure.
- This test should be performed before intestinal barium tests or after the barium is cleared from the system.
- The client should disrobe below the waist or wear a gown.
- Obtain ultrasonic gel or paste.
- The client is positioned prone in bed or on a procedure table. Very young children are positioned supine.
- The flank area is covered with ultrasonic gel, and a lubricated transducer is passed slowly over the flank area at a variety of angles and at intervals about 1–2 cm apart.
- Photographs are taken of the oscilloscopic display.
- Remove the lubricant from the skin.
- If a biopsy is performed, see Biopsy, Site-specific—Specimen ; Kidney biopsy—Specimen.
- If an antegrade pyelography or a nephrostomy tube insertion is performed with this test, see Antegrade pyelography.
Client and Family Teaching
- The procedure is painless and carries no risks (if kidney ultrasonography is not performed with invasive procedures).
- This procedure takes about 30 minutes.
Factors That Affect Results
- Dehydration interferes with adequate contrast between organs and body fluids.
- Intestinal barium obscures results by preventing proper transmission and deflection of the high-frequency sound waves.
- The more trunk fat present, the greater the attenuation (reduction in sound-wave amplitude and intensity), which interferes with the clarity of the picture. A lower frequency transducer should be used if a great deal of fat surrounds the kidney.
- Magnetic resonance urography, while much more costly, is superior to kidney ultrasonography in identifying pathology for clients with kidneys that do not opacify (such as those with renal transplants) during excretory urography.
- Proper hydration is essential for best detection. In clients who are not properly hydrated, up to 30% of obstructions and 25%–65% of hydronephrosis may not be detected.
- Further studies may include tomography or other radiographic imaging. Computed tomography is becoming the test of choice to detect kidney stones.
- Contrast-enhanced ultrasonography of the kidney is being used investigationally and shows promise as an inexpensive test for detection of lesions, lacerations, hematomas, and infections of the kidney, pancreas, and liver.
- See also Antegrade pyelography.