The kidneys (Figure 21) filter waste products from the blood. They also filter nutrients which are reabsorbed into the bloodstream. The important parts are the hilum, (containing the renal artery, vein, and pelvis) the outer cortex and the inner medulla. Unenhanced CT has proven useful in the detection of obstructing ureteral stones. The ureters descend retroperitoneally from the kidneys at the renal pelvis and enter the urinary bladder posteriorly. Unenhanced CT also requires no intravenous contrast and the examination time is very short. In addition, other conditions that can mimic ureteral obstruction can commonly be diagnosed on the exam (which would not be evaluated with an Intravenous Pyelogram, IVP). CTA appears to have a high degree of accuracy in the evaluation of renal arteries and is less invasive and costly than conventional arteriography.
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