Anatomical variations in the origin of the human ophthalmic artery with special reference to the cavernous sinus and surrounding meninges.

The origin of the human ophthalmic artery (OA) and surrounding structures was investigated in 109 cadavers by three different methods: macroscopic, stereomicroscopic, and histological observations. The following results were obtained. (1) Macroscopic observation: In 39% of the specimens the origin of the OA was observable in the cranial cavity and defined as the intradural (i.d.) type. The other 61% were named the extradural (e.d.) type. (2) Stereomicroscopic observation: In 59% of the cases, the OA originated from the internal carotid artery over or on the cavernous roof and at least a part of the OA was exposed within the cranial cavity. In the other 41% the OA originated within the cavernous wall or cavity and entered directly the optic dural sheath, thus no part of the OA was visible in the cranial cavity. Therefore, approximately 20% of the origins of the OA might be of the i.d. type, although they could not be macroscopically identified in the cranial cavity since they might emanate from the internal carotid artery between the optic canal and the optic nerve, even above the cavernous roof. (3) Histological observation: The proximal portion of the OA runs alongside the optic nerve within the subarachnoid space in the cases of the i.d. type. In contrast, the corresponding portion of the e.d. type was embedded in the dense fibrous tissue which was continuous both with the dura mater of the cavernous wall and the periosteum of the sphenoid. These anatomical data may provide important information for understanding the variety of the pathology in this region and is also useful for designing operative strategies.