Ultrasound

Ultrasound is a rapid, painless method to visualize the urinary tract. The patient requires no preparation and is not exposed to the potentially harmful effects of radiation or contrast material. The limitations of this modality include poor visualization of the ureter and difficulty in imaging obese patients. The quality of the study is both operator- and equipment-dependent. Ultrasound is an anatomic study and provides no data regarding kidney function. Renal ultrasound can document the presence, location, and size of the kidneys and detect focal parenchymal lesions such as cysts and tumors. Hydronephrosis and on occasion dilated ureters and calculi can be demonstrated (Fig, 97-1). Fluid collections surrounding the kidney can also be seen. With Doppler flow capability, vascular problems in the kidney can be identified.

Gerotas Fascia Ultrasound

FIG. 97-1. Sonogram, right uterovesicular stone with hydronephrosis. (Photograph courtesy of David Frager, M.D.)

Ultrasound is performed using a 3.5-MHz transducer. With the patient in a supine position, the transducer is placed subcostally from the lateral approach. The operator sweeps the ultrasound plane to locate the kidney. Rotation of the probe permits documentation of the longitudinal and transverse renal axes. The liver is usually used as an acoustic window to visualize the right kidney and the spleen to visualize the left. Images on the right are technically superior to those on the left because the liver provides a better acoustic window than the spleen. An air-filled stomach and dilated loops of bowel can hinder visualization. The kidneys move with respiration, and having patients hold their breath after a maximal inhalation often enhances visualization.

Gerota's fascia, the renal cortex, the collecting system, the renal sinus, as well as proximal and distal calculi can be visualized. Gerota's fascia is associated with perinephric fat and is visualized as a bright area surrounding the kidney. The renal cortex is homogeneous in appearance and more reflective (brighter) than the renal medulla. The renal pelvis is centrally located and appears echogenic. Dilation of the collecting system by fluid (echo-free) is thus readily apparent. The normal ureter is not visualized, but the dilated ureter can sometimes be seen. In the longitudinal plane, the normal kidney is football-shaped and measures 9 to 12 cm. In the transverse plane, the normal kidney is C-shaped and measures 4 to 5 cm. The kidneys normally measure within 2 cm of each other in the longitudinal axis.

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