Movements after the clinical diagnosis of brain death: supraspinal motor responses or spinal reflexes
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KeywordsCompute Tomography Angiography Brain Death Accessory Nerve Jugular Foramen Spinal Nerve Root
Computed tomography angiography.
In a recent issue of Critical Care, Wu and Orizaola Balaguer  hypothesized that nociceptive head turning after brain death (BD) is a spinal reflex. We argue that it can be a supraspinal response, which would invalidate a diagnosis of BD.
The sternocleidomastoid and trapezius are innervated by the spinal nucleus of the accessory nerve extending from the lower medulla to the ventral horn of the spinal cord (C1-C4) . Lower motor neurons from the lower medulla to C2 project to the sternocleidomastoid , contributing to the reported motor responses.
The spinal nerve roots of the accessory nerve ascend through the foramen magnum and descend through the jugular foramen. Compression of the vertebral-basilar arteries (causing intracranial circulatory arrest) and the spinal nerve roots by cerebellar tonsillar herniation at the foramen magnum would abolish the spinal accessory nerve reflex as well as cause cervicomedullary infarction.
The pyramidal tract projecting from the telencephalon controls voluntary movements. Subcortical nuclei in the diencephalon, mesencephalon, and rhombencephalon control non-voluntary movements. Complex movements are generally explained as spinal reflexes rather than supraspinal motor responses, despite an incidence of 40% to 50% in heart-beating donors . Dismissal of supraspinal motor responses is incongruent with the finding  that, on histopathological examination, about 60% of heart-beating donors have normal or minimal ischemic injury to the brainstem. If (as these histopathological findings show) the subcortical nuclei are possibly uninjured, then the supraspinal origin of movements cannot be excluded .
The absence of brainstem injury at autopsy raises doubt that all movements in BD are spinal motor reflexes. Additional histopathological data are needed to determine whether movements originate from supraspinal or spinal nuclei.
Yunfen Wu and Pedro Orizaola Balaguer
Nevertheless, we agree with Rady and Verheijde that a supraspinal origin of head-turning movements in our patient cannot be ruled out. In regard to the involved source of such movements in BD, we suggested in our previous report that further studies (including hispatological examination) are needed for this to be clarified.
YW and POB thank the Radiology Department of Hospital Universitario de Marqués de Valdecilla for technical and analytical support with the CTA images. Written consent to publish was obtained from the patient’s next of kin.
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