Opening the Arachnoid

Very gentle retraction is applied to the frontolateral orbital aspect of the frontal lobe to demonstrate the carotid cistern. The latter is usually opened between the optic nerve and internal carotid artery using a round-bladed 

The arachnoid over and lateral to the internal carotid artery and A-1 segment are opened next, releasing more CSF and enabling the surgeon to check the size, position and variations of the PcoA, AchoA, uncal artery and oculomotor nerve. 

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