Sphenoidal artery: review of the literature and analysis of a dissected arterially injected fetal orbit

Abstract

Purpose: The sphenoidal artery is considered a component of the complex and dangerous arterial anastomoses of the human orbitocranial region, particularly with the advent of interventional neuroimaging. The objective of this publication was to analyze the various descriptions of the sphenoidal artery in the literature as related to relevant photographs of a dissected arterially injected fetal middle cranial fossa and orbit.

Methods: Publications dealing with middle meningeal-ophthalmic arterial anastomoses, focusing on the sphenoidal artery, were reviewed. A relevant dissection of a fetal specimen was analyzed.

Results: The literature dealing with the sphenoidal artery is at times not in agreement. The nomenclature and anatomy of its passage through the superior orbital fissure or Hyrtl canal have variable descriptions. Photographs of the skull base of a dissected arterially injected fetal specimen show bilateral prominent orbital branches of the middle meningeal arteries. These branches entered both orbits in a course similar to the diagrammatic representations of the sphenoidal artery, and give rise to several major intraorbital arteries. This study provides the only photographic image in the literature of this variation in a human fetal anatomic dissection.

Conclusions: Review of the literature dealing with the sphenoidal artery shows inconsistent nomenclature and conflicting descriptions of its anastomotic connections, and varying evolutionary and embryologic theories. Analysis of the dissected fetal skull base indicates that the sphenoidal artery is not a distinct artery but just a middle meningeal orbital arterial branch, an important component of the complex and dangerous arterial anastomoses of the human orbitocranial region.

Keywords: Hyrtl canal; Middle meningeal artery; Ophthalmic artery, orbit; Sphenoidal artery; Superior orbital fissure.

Fig. 1

Photograph of the skull base of an 18 weeks’ gestational age specimen, with a crown–rump length of 150 mm and occipito-frontal diameter of 50 mm. The dissection demonstrates the anterior branch of the middle meningeal artery (MMA), injected with a barium–gelatin contrast agent, exiting the foramen ovale (FO) in both middle fossae. The anterior branches divide into the orbital branches (OB) which pass anteriorly to disappear below the posterior edge of the lesser wing of the sphenoid bone. A dashed arrow points to a segment of transparent ruler. The distance between two black lines on the ruler is 1 mm

Fig. 2

Photograph of the same specimen as in in Fig. 1. Following further dissection of the partially ossified sphenoid bone and removal of the orbital roofs, the prominent orbital branches of the middle meningeal arteries (yellow short arrows) course though the dissected sphenoid bones and enter both orbits, in a course similar to the diagrammatic representations of the so-called sphenoidal artery. The middle meningeal orbital branches divide within the orbit. On the left side, following removal of the roof of the optic canal, an extremely thin ophthalmic artery (white short arrows) originating from the internal carotid artery (ICA), passes underneath the main orbital middle meningeal branch towards the region of the left lacrimal gland (LG). Also visible are a number of small branches (dashed small yellow arrows) originating from the intra-sphenoid middle meningeal orbital artery, coursing towards the region of the lacrimal gland (LG). No ophthalmic artery was identified on the right side. The dashes white arrow points to the dissected anterior clinoid. As the sphenoid bone is partially ossified at this developmental stage, the SOF and HC could not be identified. The distance between two blue lines on the white ruler segment is 1 mm, indicating the small size of some of the visualized vasculature