The brain mass commonly is increased (1.6-1.8 kg), but the increase is definitely a function of time on the respirator (Schneider 1970; Walker 1985).
Depending on the primary cause of ischemia and time on the respirator, the following macroscopic changes are observed: a distinct swelling of the total brain (Fig. 15.1a); the cerebrum may be well-preserved and gray-colored (Fig. 15.1b) or a nondescript friable or mushy mass; the swollen and congested cerebral hemispheres have a dusky hue; the
Fig. 15.1a-c. Gross external findings in respirator brain. a Extreme brain swelling (autopsy specimen); b the external surface may be well preserved, and is gray colored with indications of different regional no-reflow phenomena (formalin-fixed specimen); c distinct indications of herniation with uncal and tonsillar necrosis are seen
Fig. 15.1a-c. Gross external findings in respirator brain. a Extreme brain swelling (autopsy specimen); b the external surface may be well preserved, and is gray colored with indications of different regional no-reflow phenomena (formalin-fixed specimen); c distinct indications of herniation with uncal and tonsillar necrosis are seen leptomeninges often show a quantitatively different extent of congestion and fibrin precipitation as an indication of different regional no-reflow phenomena (Fig. 15.1b); transtentorial herniations are com mon (Fig. 15.1c). Gross sections of the brain show a lead-colored, grayish cortex, a partly extreme compressed ventricular system, and sometime focal hemorrhages in white and/or gray matter, which is demonstrated in Fig. 15.2a, b in comparison with a normal-colored edematous brain section after formalin fixation. The brain stem is often torn and is characterized by congestion and hemorrhages; the softened herniated cerebellar tonsils are commonly necrotic (Fig. 15.3b), with necrotic tissue of tonsil-lar cerebellum lodged along the spinal cord anywhere from the cervical segment to the cauda equina (Fig. 15.3c-e). This phenomenon is considered characteristic of brain death lasting more than 36 h (Schneider and Matakas 1973) and may be one neu-ropathologic-diagnostic sign of brain death (Sayer et al. 1981). In addition, hemorrhagic softening of the upper few segments of the cervical spinal cord occurs, but is often overlooked if that part of the cord is not dissected. In about 10% of cases, the cut sections appear grossly normal, but in more than half of brains the white matter is edematous and soft (Fig. 15.3f).
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