Interdural origin of the ophthalmic artery at the dural ring of the internal carotid artery. Report of two cases.

The authors report two cases in which the ophthalmic artery (OA) originated from the interdural portion of the internal carotid artery at the carotid dural ring and coursed within the dura. This configuration was observed during surgeries performed in 82 cases of juxta-dural ring aneurysms. In surgery for such an aneurysm, if the OA is not seen intradurally, an attempt should be made to find this kind of variation by using a Doppler flowmeter before sectioning the dural ring.