The functional basis for nephrographic patterns in acute tubular necrosis.

There is considerable evidence that the principal functional abnormality in patients with acute reversible renal failure (ARF, or "acute tubular necrosis") is reduced cortical perfusion with diminished glomerular filtration. However, in such patients, high-dose intravenous urograms most commonly show an immediate obvious nephrogram. Since nephrographic density is believed to depend on the filtration of contrast medium into the tubular lumen, it is difficult to reconcile the early development of the nephrogram if glomerular filtration is reduced. Extensive experiments with both mercuric chloride and glycerol rat models of ARF have confirmed rapid intraluminal accumulation of contrast medium, albeit in reduced amounts. Studies using the normally filtered compound sodium nitroprusside and its precipitation as "prussian blue" suggest rapid transtubular diffusion from peritubular capillaries in kidneys with ARF. This, it is suggested, is also the mechanism for the rapid intraluminal ingress of contrast media and explains the early appearance of nephrogram. The less common intravenous urogram finding in ARF of a slowly developing and increasingly dense nephrogram may then represent cases with only slight tubular necrosis with predominant reduction in glomerular filtration.