To study the spatial structures among the bony structures, muscles, nerves, and arteries in the cranio-orbital region by microdissection, and to provide anatomical basis for neurosurgery in this area.

A total of 8 adult (16 sides) cadaveric head specimens were selected. The cranio-orbital region was exposed layer by layer using a curved incision via the frontotemporal orbito-zygomatic approach. The anatomical structure of the cranio-orbital junction region was observed and the data related to the supraorbital fissure were documented. The bone structures, muscles, nerve courses ophthalmic arteris anatomy and their position relationship were obserred. The diameters of the nerves entering the orbit through the supraorbital fissure were measured as well.

The cranio-orbital junction region was located below the anterior clinoid process. The optic canal connected the cranial fossa and the orbit. The supraorbital fissure connected the orbit to the middle cranial fossa. The lengths of lateral, medial, and superior margins of the supraorbital fissure in the eight cadaveric head specimens were 18.4±6.2 mm, 7.7±1.6 mm, 16.4±5.6 mm respectively. The widths of the supraorbital fissure on the left side and right side were 3.64±0.86 mm and 3.69±0.88 mm respectively. The widths of the left and right supraorbital fissures were 3.64±0.86 mm and 3.69±0.88 mm respectively. The orbital wall consisted of 7 bony structures: frontal bone, zygomatic bone, ethmoid bone, lacrimal bone, pterygoid bone, palatine bone and maxillary bone. The orbit had a roof, a floor, a medial wall and a lateral wall. Except for the medial wall, the other walls had symmetrically arranged bony structures. The extraocular muscles included 7 muscles: levator palpebrae, rectus superioris, rectus inferioris, rectus medialis, rectus externus, obliquus superioris and obliquus inferioris. The intraorbital nerves mainly consisted of 7 nerves: the optic nerve, the trochlear nerve, three branches of the ophthalmic nerve (frontal, lacrimal and nasociliary nerves), the abducens nerve and the oculomotor nerve (upper and lower branches). Except the optic nerve passing through the optic canal, other 6 nerves (7 branches in total) entered the orbit through the supraorbital fissure and their diameters were 0.86±0.42 mm, 1.51±0.53 mm, 0.71±0.36 mm, 0.82±0.47 mm, 1.23±0.41 mm, 1.29±0.48 mm and 1.82±0.48 mm respectively. The ophthalmic artery which was located below the optic nerve entered the orbit through the optic canal. A total of 16 ophthalmic arteries were observed in 8 specimens. In 1 case there was a duplicated trunk and the distance between the upper and lower trunks was 11.2 mm. In the remaining 7 cases, there were single-trunk ocular arteries. The intraorbital segment of ophthalmic artery was divided into 3 segments according to the angle and curvature of ophthalmic artery. The spatial correlations of the bony structures, muscles nerve courses, and ophthalmic arteries were basically constant.

The anatomy of the cranioorbital region is complicated and its space is narrow. Proficiency in the microanatomy and spatial correlations of the region would help physicians protect important anatomical structures during surgery and particularly lower duplicate ophthalmic artery.

Orbit; Optic nerve; Ophthalmic artery; Superior orbital fissure; Ophthalmic artery microanatomy