Acute tubular necrosis (ATN) is a medical condition involving the death of tubular epithelial cells that form the renal tubules of the kidneys. ATN presents with acute kidney injury (AKI) and is one of the most common causes of AKICommon causes of ATN including low blood pressure and use of nephrotoxic drugs. The presence of "muddy brown casts" of epithelial cells found in the urine during urinalysis is path gnomonic for ATN. Management relies on aggressive treatment of the factors that precipitated ATN (e.g. hydration and cessation of the offending drug). Because the tubular cells continually replace themselves, the overall prognosis for ATN is quite good if the underlying cause is corrected, and recovery is likely within 7 to 21 days. ATN may be classified as either toxic or ischemic. Toxic ATN occurs when the tubular cells are exposed to a toxic substance (nephrotoxic ATN). Ischemic ATN occurs when the tubular cells do not get enough oxygen, a condition that they are highly sensitive and susceptible to, due to their very high metabolism.Acute tubular necrosis is classified as a "renal" (i.e. not pre-renal or post-renal) cause of acute kidney injury. Diagnosis is made by a FENa (fractional excretion of sodium) > 3% and presence of muddy casts (a type of granular cast in urinalysis. On histopathology, there is usually tubulorrhexis, that is, localized necrosis of the epithelial lining in renal tubules, with focal rupture or loss of basement membrane. Proximal tubule cells can shed with variable viability and not be purely "necrotic Ischemic ATN can be caused when the kidneys are not sufficiently perfused for a long period of time (i.e. renal artery stenos is) or during shock. Hypo perfusion can also be caused by embolism of the renal arteries. Given their importance in massive nutrient and electrolyte reabsorption, the proximal tubule and medullar thick ascending limb require significant ATP and are most susceptible to ischemic damage. Thus, ischemic ATN specifically causes skip lesions through the tubules