The normal anteroposterior diameter of the aorta is 3 cm or less when measured from outer wall to outer wall. Most aneurysms are fusiform or show uniform dilatation of the entire circumference of the vessel. Aneurysms usually arise below the level of the renal arteries and are left of the midline. Their anterior expansion usually creates a good sonographic window because they push the bowel aside. The gallbladder is identified as a sonolucent, oblong, pear-shaped sac that is normally posteromedial to the right lobe of the liver.
Gallstones usually lie in the most dependent part of gallbladder.
Acute cholecystitis Cholelithiasis alone does not represent acute cholecystitis. Asymptomatic stones are common. The renal parenchyma has uniformly low echogenicity, which usually is less than that of the adjacent liver and spleen. Ultrasonography can help in the difficult differentiation of renal colic from an aneurysm. Ultrasonography also can aid in determining the number of kidneys and the presence of anatomic anomalies.