The pathologic entity called brain purpura (pericapillary encephalorrhagia), incorrectly referred to as “hemorrhagic encephalitis,” consists of multiple petechial hemorrhages scattered throughout the white matter of the brain. The clinical picture is that of a diffuse encephalopathy, but diagnosis is essentially a pathologic one. Blood does not appear in the CSF, and the condition should not be confused with a stroke. The pathologic appearance is highly characteristic. The lesions in brain purpura are small, 0.1 to 2.0 mm in diameter, and are confined to the white matter, particularly the corpus callosum, centrum ovale, and middle cerebellar peduncles. Each lesion is situated around a small blood vessel, usually a capillary. In this para-adventitial area, both the myelin and axis cylinders are destroyed, and the lesion is usually though not always hemorrhagic. Fibrin exudation, perivascular and meningeal infiltrates of inflammatory cells, and widespread necrosis of tissue are not observed. In these respects, brain purpura differs fundamentally from acute necrotizing hemorrhagic leukoencephalitis. Usually the patient becomes stuporous and comatose without focal neurologic signs.
The etiology of brain purpura is quite obscure and there may be several causes. It may complicate viral pneumonia, uremia, promyelocytic leukemia, arsenical intoxication, and, rarely, metabolic encephalopathy and sepsis, or there may be no associated disease. Amyloid angiopathy and an uncharacterized cerebral small vessel disease also have caused this picture of a multiplicity of small hemorrhages. Primary or secondary thrombotic thrombocytopenic purpura (TTP) may be the final common pattern for this entity.
A degree of brain hemorrhage is to be expected in acute hemorrhagic leukoencephalitis (Hurst type), which represents an extreme form of acute disseminated encephalomyelitis (see Chap. 35), and in herpes encephalitis (see Chap. 32). The other rare types of hemorrhages, listed in Table 33-8, are self-explanatory.
Hemorrhages of intraspinal origin, all of them rare, may be the result of trauma, AVM (the usual cause of nontraumatic hematomyelia), dural AV fistula, anterior spinal artery aneurysms, or bleeding into tumors such as hemangioblastoma. Spinal subarachnoid hemorrhage from an AVM may simulate an intracranial subarachnoid hemorrhage, causing a stiff neck, headache, and even subhyaloid hemorrhages. Subarachnoid hemorrhage in which interscapular or neck pain predominates should raise the suspicion of an aneurysm of the anterior spinal artery or of a spinal AVM or cavernous angioma. Angiographic study of the radicular spinal vessels and the origins of the anterior spinal arteries from the vertebral arteries may disclose the source of bleeding. Extradural and subdural spinal extravasations may be spontaneous (sometimes in relation to rheumatoid arthritis) but are far more often a result of trauma, anticoagulants, or both. Extradural spinal hemorrhage causes the rapid evolution of paraplegia or quadriplegia; diagnosis must be prompt if function is to be salvaged by surgical drainage of the hematoma. These entities are discussed further in Chap. 42.