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Bilateral Posterior Cerebral Artery Occlusions: Cortical Blindness

Cortical blindness

Visual cortex infarction
The lucent (blacker) areas in the occipital region of this computed tomographic (CT) study reflect loss of tissue.

The distribution of the abnormal tissue conforms perfectly to the territory supplied by the calcarine arteries, branches of the posterier cerebral arteries.

There are many causes of infarction in this region, among them emboli from the vertebral arteries or heart and, as in this case, a subdural hematoma that caused the brain to herniate and compress both posterior cerebral arteries.

Cortical blindness
This patient might well have been completely blind ("cortically blind"), because the visual cortex lies in the medial occipital region that has been infarcted. Pupils would have reacted normally to light and the eyeballs would have looked normal.

Actually, this patient was not completely blind. The posterior visual cortex was spared in both eyes, owing to collateral supply from the middle cerebral arteries—a common phenomenon. He had small islands of central vision in both visual fields which allowed him normal visual acuity. But he groped about like a blind man because his eccentric vision was gone. Because of his normal visual acuity and normal ocular examination, yet groping navigation, he was thought to be malingering!

What to do?
Any patient with acute persistent hemifield or binocular vision loss should undergo immediate brain imaging. MRI is preferable to CT.

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