Specificity of radionuclide brain blood flow testing in brain death: case report and review

Brain blood flow tests with diffusible radiopharmaceuticals are often done as an ancillary test in brain death (BD). We report a case of an infant with absent brain blood flow on an anterior planar image despite persistent breathing and extensor posturing. We reviewed the literature from 1980 to 2008 using MEDLINE and PubMed to determine the sensitivity and specificity of these tests in the diagnosis of BD. Search terms were any combination of: brain death; and single photon emission computed tomography (SPECT), radiopharmaceuticals, technetium Tc 99m exametazime, or organotechnetium compounds. The sensitivity of absent brain blood flow on planar imaging for clinically confirmed BD is 119/153 = 77.8% [95% CI 70.5%-83.7%]; and the specificity is 41/41 (100%) [95% CI 92.6%-100%]. For clinically confirmed BD, the sensitivity of SPECT is 107/121 (88.4%) [95% CI 81.4%-93.1%], and specificity is 12/12 (100%) [95% CI 78.4%-100%]. For contrast angiography confirmed BD, the sensitivity of SPECT is 34/34 (100%) [95% CI 91.2%-100%]; the specificity could not be estimated as there were no patients without clinical BD having both tests. Case reports emphasized the possibility of isolated posterior-fossa blood flow, which would not be detectable using non-diffusible radiopharmaceuticals, or without a lateral view using diffusible agents. We conclude that patients having an ancillary radiopharmaceutical brain blood flow test for BD should have anterior and lateral views without exception. Larger numbers of patients both with and without BD (but with severe brain injury) must be studied to determine the sensitivity and specificity of these tests