On the fifth day postoperatively, visual acuity was light perception in the right eye and 20/100 in the left eye. Automated visual field testing revealed a temporal defect in the left eye (Fig. 3A). The patient underwent transthoracic echocardiography and carotid Doppler examination, both of which failed to demonstrate a possible source of emboli.
Perioperative visual loss among patients undergoing nonocular surgery occurs in less than 0.001% of cases (3,4), whereas the prevalence of visual loss after cardiac surgery is estimated to be 100 times greater (5-7). The most commonly affected site is the optic nerve with the mechanism being ischemic in origin. If the optic chiasm is involved, it may be the result of an expanding sellar or parasellar mass, such as pituitary apoplexy or a rapidly expanding adenoma (8). An ischemic insult to the chiasm is a rare event due to the fact that the chiasm is supplied by an extensive network of collateral cerebral blood vessels originating from the circle of Willis.
Our patient experienced loss of vision following AVR surgery under general anesthesia. MRI showed multiple ischemic foci in the brain, as well as a right-sided chiasmal infarct involving the prechiasmal portion of the right optic nerve. Visual field examination confirmed a right anterior junction syndrome (9). Although no definite source was found, we assume that the insult is most likely embolic in nature. Cerebral emboli have been reported to occur frequently following cardiopulmonary bypass procedures and confirmed both with fluorescein angiography (10) and autopsy studies (11,12).
Anatomic studies have detailed the complex blood supply of the chiasm and visual pathways (1,2). This rich vascular network includes 2 major components, a superior group and an inferior group. The superior group of vessels emanate from the anterior cerebral arteries and occasionally anterior communicating arteries, whereas the inferior blood supply is derived from branches of the internal carotid artery, basilar, posterior cerebral, and posterior communicating arteries. The complex nature of this network is characterized by numerous anatomical variations, collateral feeders, and crossing-over phenomenon (1). Based on the location of the chiasmatic infarct in our case, we propose involvement of branches arising from the A1 segment of the right anterior cerebral artery or from the distal right internal carotid artery.
In conclusion, MRI, and DWI in particular, may play a valuable role in evaluating patients with perioperative visual loss due to ischemia of the anterior visual pathways.
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