Spurious identification of critical intercostal arteries by evoked responses during aortic resection.

A patient with an acute dissection of the thoracic aorta is described. Intraoperative evoked-response evaluation suggested the presence of a critical intercostal vessel in the excluded segment, but no major vessel could be identified. Expedient grafting and reestablishment of flow led to prompt recovery of the evoked response, suggesting that mechanical distortion of the aorta by the distal cross-clamp led to a compromised flow through a subadjacent intercostal artery that was an important source of cord perfusion. Recognition of this possibility is important because it may prevent time-consuming attempts to implant small vessels in the excluded segment, which are not major contributors to spinal cord blood flow.