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Secondary Brain Stem Hemorrhage

Secondary brain stem hemorrhages are caused by a rapid increase in axial pressure produced by supra-tentorial space-occupying processes such as dura hemorrhages, intracerebral hemorrhages or severe cerebral edema (cf. Chap. 7, p. 123). Those expanding processes can unilaterally or bilaterally compress, displace, and distort the brain stem (Fig. 9.23b, c; see also Figs. 4.8a, 4.11a, 7.10e). Stretching of the upper pontine arteries and veins results in ischemia. Additional distortion leads to rupture and hemorrhage into the rostral portion of the pons and the midbrain. Sudden decompression of the intact ischemic pons may cause bleeding into the necrotic tissue. Lesions or masses that slowly expand or decompress permit adaptive reactions that may prevent subsequent massive hemorrhage. A further factor may also play a role, namely structural degeneration secondary to mechanical loading at a distant portion of the cerebrum, a supratentorial hemorrhage for example. A non-mechanically induced increase in axial pressure with a space-occupying process such as edema, tumor or spontaneous hemorrhage may also result in brain stem hemorrhage (an American type of "Duret hemorrhage").

Pathogenically, secondary brain stem hemorrhage is explained as follows:

— Venous congestion leads to bleeding in the middle portions of the brain stem. The hemorrhages are often located between the caudal parts of the substantia nigra and aqueduct. They occur if the arterial blood supply remains intact while venous drainage is impeded by the arrested supratentori-al circulation (Matakas 1975). The morphology is characterized by bleeding and/or necrosis in the center of the brain stem, including lateral parts

Fig. 9.20a-c. Intracerebral hemorrhages - two cases. a, b Extensive subarachnoid hemorrhage associated with an intracerebral hemorrhage, originating from a mechanically induced cortical hemorrhage at the frontal basis. c Two centers of hemorrhage -in the white matter (left) and in the basal ganglia (right)

Fig. 9.20a-c. Intracerebral hemorrhages - two cases. a, b Extensive subarachnoid hemorrhage associated with an intracerebral hemorrhage, originating from a mechanically induced cortical hemorrhage at the frontal basis. c Two centers of hemorrhage -in the white matter (left) and in the basal ganglia (right)

of the pons (Fig. 9.23b), or of the periventricular tissues (Fig. 9.23c).

— The herniation process leads to tonsile strain of the horizontal running small arteries which supply the brain stem by pressure and capillaries will rupture.

Fig. 9.21a-c. "Gliding contusions" in three cases as demonstrated by cleft-like hemorrhages in the white matter of the first frontal gyrus

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