Morphology and morphogenesis of cerebral ring hemorrhages in anemic monkeys

Cerebral ring hemorrhages were observed in four species of monkeys with various forms of anemia. The lesions resembled those described in humans with a variety of diseases, including pernicious anemia. The pale centers of most lesions were surrounded by rings of erythrocytes. Also observed were petechiae, pale foci without hemorrhage, and glial nodules. Ultrastructural study revealed that the pale cores were foci of degenerating neurites associated with infiltration of fibrin into the finest interstitial spaces. Leakage of firbinogen and erythrocytes apparently occurred from capillary sized vessels. A few of these were thrombosed, some were normal and some had only small fibrin thrombi in apparent apposition to damaged endothelial tight junctions. These findings suggest that a primary effect of anemia and other insults associated with ring hemorrhages is damage to tight junctions. Consequent fibrinous exudation clogs the interstitium and results in neuritic degeneration.