During repair of a Type I or II Thoracoabdominal Aortic Aneurysm, it is inappropriate to monitor spinal cord motor function by recording neurogenic responses to stimulation of the cervical or high-thoracic spinal cord.
As early as 1988, it was documented in the animal data that responses to cervical cord stimulation were not mediated by the corticospinal tract (Zapulla, et al). In 1990, Machida et al showed that sensory pathway responses remained intact and motor responses were immediately abolished in the lower extremities after ligation of the arteria radicularis magna - the primary feeder from the aorta to the anterior spinal artery (J Spinal Disorders. 1990 Dec;3[4]:345-52). In 1992, Su et al asserted that neurogenic responses in the legs to cervical cord stimulation were mediated by antidromic "back-firing" of the dorsal columns. This would be analogous to a backwards SSEP.
In the human data, both Toleikis (2000) and Deletis (2001) independently showed that such responses in the legs could be cancelled by performing sensory collision studies. In 2001, Minahan et al reported a few cases in which patients had emerged from spinal cord surgery with paraplegia even after they had "normal" responses to cord stimulation (click on the title of this post). These findings suggest that stimulation of the cord results in responses mediated by antidromic sensory activation and do not represent orthodromic motor activity.
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