4.1.1 Hemodynamic ATN

Definition: Morphological lesions of the kidney with acute renal failure due to hypoperfusion.

The morphological lesions are patchy at least in the beginning. The straight part of the proximal tubule and the ascending limb of Henle`s loop are mostly affected. Light microscopy at low power magnification shows nothing but a slight dilatation of the tubular lumens accompanied later by a thinning of the tubular epithelium.  High power magnification exhibits a focal, rarely diffuse, loss of the brush border in the proximal tubules and  blebs (desquamated apical cell fragments) in the tubular lumens. In the distal tubules hyaline casts (Tamm Horsfall protein casts) are present in variable numbers and may even be found in the interstitium (often surrounded by some lymphocytes and histiocytes). Slight interstitial edema may be present as well. In  the outer medulla blood stasis in the vasa recta may be prominent and mononuclear cells (myeloid precursor cells) may be found in the medulla, which is rarely seen in biopsies.

In later stages scattered but always sparse interstitial infiltrates mainly on the cortico-medullary junction are present. Plasma cells, eosinophils and neutrophils are mostly absent. In patients with longstanding acute renal failure of more than three weeks a more prominent widening of the interstitial space with minimal interstitial fibrosis very poor in cells may ensue.