Tc-99m hexamethylpropylene amine oxime scintigraphy in the diagnosis of brain death and its implications for the harvesting of organs used for transplantation.

PURPOSE

Diagnosing brain death is important in managing the comatose patient for whom the continuation of life support is being questioned and when organ harvesting is being considered. The virtual immediate localization of Tc-99m HMPAO to cerebral and cerebellar tissue provides an index of blood perfusion, and its absence denotes brain death. Other methods for assessing brain death include cerebral angiography, MRI, CT imaging after inhalation of stable xenon, electroencephalography, and clinical examination. The contrast material used for angiography may damage harvested organs, and the other studies have significant errors. MRI, CT imaging, and angiography are unsuitable for bedside use.

METHODS

Twenty-three patients, who presented with head trauma, prolonged anoxia or intrinsic brain disease (e.g., glioblastoma multiforme) and who were brain-dead by clinical examination criteria, were referred to the nuclear medicine division for verification of brain death. For adults, approximately 25 mCi Tc-99m hexamethylpropylene amineoxime (HMPAO) was administered intravenously. All patients but one were imaged using a mobile scintillation camera at the bedside.

RESULTS

We demonstrated (1) both cerebral and cerebellar perfusion, (2) neither cerebral nor cerebellar perfusion, (3) cerebral without cerebellar perfusion, and (4) cerebellar without cerebral perfusion. Patients without cerebral perfusion were diagnosed as brain-dead. The significance of a viable cerebellum in the absence of cerebral viability was not fully appreciated, although organs were harvested from such patients. We determined how well the clinical examination criteria held up in the diagnosis of brain death against the new gold standard of Tc-99m HMPAO scintigraphy: Clinical examination criteria correctly predicted brain death only 83% of the time compared with HMPAO scintigraphy.

CONCLUSIONS

Brain death assessment by Tc-99m HM-PAO scintigraphy has proved to be a reliable, safe, and cost-effective bedside method and may have practical application in the assessment of brain death in potential cadaveric donors.