99mTc-HMPAO SPECT in the diagnosis of brain death

Objective: To evaluate the effectiveness of single proton emission tomography (SPECT) with ^99mTc-HMPAO in the diagnosis of brain death (BD). Design: Prospective study in comatose and brain-dead patients. Setting: Neurologic ICU. Patients and methods: Fifty comatose patients (age range: 10 days-75 years) were submitted to SPECT study. In 21 of them (42%) reversible factors (e.g., influence of drugs affecting the central nervous system) were present. Thirty-eight patients were clinically brain-dead, while the remaining 12 were tested both in pre-terminal conditions and after the clinical onset of BD. Interventions: Brain SPECT following i.v. injection of ^99mTc-HMPAO (300-1100 MBq), using a 4-headed gamma-camera (20 min, 360°, 88 images). Measurements and results: All patients tested in pre-terminal conditions showed preserved brain perfusion. Two of them had flat EEGs despite the absence of any reversible cause of coma; three patients survived, but remained in persistent vegetative states. SPECT confirmed the diagnosis of BD in 45 out of 47 patients (95.7%), clearly showing the arrest of brain perfusion (picture of 'empty skull'); in two clinically brain-dead children (aged 10 days and 12 months, respectively) weak perfusion of the basal ganglia, thalamus and/or brain stem was still present, precluding the diagnosis of BD; both of them died a few days later. Conclusions: Our results confirm the reliability of SPECT in the diagnosis of BD. A problem arises about its effectiveness in brain-dead children, but this seems to be a matter of definition of BD and cerebral viability, rather than a limit of SPECT.