Findings on Tc-99m HMPAO brain imaging in brain death.

Abstract

Tc-99m hexamethylpropylene (HMPAO) brain imaging for brain death has been well established and criteria for brain death include: absent flow through internal carotid, middle cerebral and anterior cerebral arteries on flow study, and absence of uptake in the cerebrum and cerebellum in the static images. However, the scintigraphic findings of the brain death determined brain death in the first radionuclide study, which is not always straightforward. A second study was required 24 hours later. Three unusual scintigraphic presentations on the first radionuclide study are illustrated. Patients with presence of perfusion in one part of the brain such as a lack of supratentorial perfusion and preservation of intratentorial perfusion, supratentorial and intratentorial blood flow dissociation, or presence of perfusion in one cerebral hemisphere, indicated preservation of one portion of brain function. Accordingly, it cannot yet be considered dead, although the prognosis is poor and death may occur within a short time. In such a situation a repeated study is necessary. A six-year-old boy with a motor vehicle accident injury shows normal cerebral flow with a small defect on the right cerebral hemisphere. The linear defect in one cerebral hemisphere was unexpected. The accurate and timely assessment of brain death is critical decision-making from medical, legal, ethical, and financial perspectives. Tc-99m HMPAO cerebral flow study and static brain images are reliable noninvasive methods for confirmation of brain death. Initial Tc-99m HMPAO brain imaging in a patient after a motor vehicle accident showed only a minor reduction of cerebral perfusion in the right cerebral hemisphere. Repeat imaging 48 hours later showed absent cerebral and cerebellar blood flow. In another patient, cerebellar flow was initially seen, but 24 hours later there was no cerebral or carebellar flow, A third patient shows an even more pronounced dissociation of initial and 24-hour images. Thus, serial imaging is important for the monitoring of patients suspected to be brain dead on the basis of radionuclide imaging.