The histologic section of this patient's lung shows an aggregate of fat globules, hematopoietic cells, and organizing thrombus lodged inside the pulmonary vasculature.  This is consistent with bone marrow embolism, which occurs in fat embolism syndrome (FES).

FES classically presents with the triad of respiratory distress, neurologic impairment, and petechial rash within 24-72 hours following a long-bone or pelvic fracture.  Severe skeletal injuries can cause fat globules to be dislodged from bone marrow into the bloodstream, where they form aggregates with platelets and red blood cells.  These aggregates occlude pulmonary microvessels and impair gas exchange.  Some fat emboli may be small enough to pass through the pulmonary circulation and cause microvascular occlusion in the systemic circulation, leading to the neurologic manifestations (eg, confusion) and petechial rash characterizing the condition.  Release of toxic inflammatory mediators (eg, cytokines, free fatty acids) may also contribute to the neurologic manifestations and rash.  Thrombocytopenia can occur due to platelet adherence and aggregation to circulating fat globules.