The most important histopathologic pattern in lung disease is Acute Injury.  When a lung biopsy shows 1) Fibrin, 2) Edema, 3 Focal organization and 4) reactive type 2 cell proliferation, all other patterns and observed changes are subordinate.  Acute injury is associated most often with acute respiratory distress. When such distress is recalcitrant to empiric therapy, a lung biopsy may be required.  Addressing the potential causes of Acute Injury is therefor the primary goal for the pathologist.  The Litany of causation is "First look for bugs (infection), then rule out drugs (toxicity), if no results, get an ANA, CRP, and Erythrocyte Sedimentation Rate to rule out acute automimmune disease and finally, consider the idiopathic form of acute lung injury "Acute interstitial pneumonia".