An unusual cause of fixed dilated pupils after cardiac surgery.

BACKGROUND: The presence of fixed, dilated pupils after cardiac surgery is an ominous sign, typically indicating severe diffuse hypoxic-ischemic brain injury. Rarely, however, this finding can be seen as a result of focal midbrain ischemia. It is important to differentiate between these syndromes, as the latter might be amenable to acute stroke treatments, and because they affect consciousness very differently. CASE: A 46-year-old man with diffuse atherosclerosis underwent coronary artery bypass grafting and closure of an incidentally discovered patent foramen ovale. He underwent neurologic evaluation on post-operative day 6 because he was not speaking and appeared to have a new right hemiparesis. Eye movements, pupillary, and lid function were all normal at this time. MRI showed multiple posterior circulation infarcts, involving both cerebral peduncles. On post-operative day 12, he became unresponsive, quadriplegic, and had bilaterally fixed, dilated pupils. CT showed low attenuation in nearly the entirety of both cerebral peduncles. DISCUSSION: Midbrain infarction is rare. Bilateral midbrain infarction is even rarer and typically presents as locked-in syndrome with preservation of pupillary function and at least vertical eye movements. In our review of the literature, we found only three other cases of midbrain infarction associated with bilateral mydriasis. As in our case, these characteristically involved the anteromedial midbrain bilaterally.
CONCLUSIONS: Fixed, dilated pupils after cardiac surgery can rarely be caused by bilateral anteromedial midbrain infarctions. It is important to differentiate this from the much more common diffuse hypoxic-ischemic injury.