Approach to the urogenital system

Anatomy

The oval-shaped kidneys, measuring 9 to 15 cm in length and 4 to 6 cm in width, are located in retroperitoneum between the 12th thoracic and 4th lumbar vertebrae, just lateral to the psoas muscles. The kidneys are surrounded by the Gerota fascia (echogenic capsule) and a fat layer of variable thickness. Ultrasound examination, in both longitudinal and transverse planes, is performed using convex or microconvex (2.5-5 MHz) transducers and identifies the hilum, containing renal vessels and ureter; the pelvis, receiving two to three major calyces; and the cortex and the medulla, containing renal pyramids. Normal cortical echogenicity should be less than or equal to the echogenicity of liver ( Figure 42-1 ). The right and left kidneys are visualized in the right (midaxillary line) and left (posterior-axillary line) lower intercostal spaces, respectively. The right kidney is lower than the left one because of the right lobe of the liver. In the intensive care unit (ICU), intercostal ultrasound approaches as well as scans along both hypochondriac regions can be used.

The right and left main renal arteries (RAs) originate laterally from the abdominal aorta, inferior to the superior mesenteric artery (SMA). Segmental (lobar) arteries originate before or immediately after entering the kidney, and their branches (interlobar arteries) travel through the kidney parenchyma. The right and left renal veins (RV) originate off the inferior vena cava (IVC). Ureters travel retroperitoneally, crossing over the iliac vessels and along the pelvic sidewalls, before curving anteriorly and medially at the level of ischial spines, and thus entering the bladder at ureterovesical junction. Ureters are not well visualized by ultrasound but, when distended (hydroureter), appear as hypoechoic, tubular structures ( Figure 42-2 ). The round-shaped bladder is depicted by ultrasound just above the pubis. When not distended, its wall appears thickened. When fully distended, its wall should measure less than 0.4 cm thick. The trigone is a triangular region of the bladder base, formed by two ureteral orifices and the internal urethral orifice, which are identified by depicting ureteral jets, emanating from the ureters. In critical care patients, the balloon of the Foley catheter should be visible in the bladder (catheter is clamped to avoid bladder emptying, Figure 42 E-1 ). Inability to visualize the balloon should prompt a search for its location because extravesical inflation may result in local trauma and confusing appearances. The normal adult testis measures about 3 to 4 cm (longitudinal section) and is normally hypoechoic. The upper testicular pole is capped with the head of the epidydimis. A thin rim of anechoic fluid may be seen around the testicle.

Disorders