Quantitation of and measurements utilizing the sphenoid ridge

The sphenoid ridge (posterior aspect of the lesser wings) is encountered in many intracranial procedures. Increased knowledge of its morphology and relationships is, therefore, of importance to the neurosurgeon and clinician who appreciate imaging of this anatomical region. We have quantitated this part of the sphenoid bone in dry human skulls (35) and made cadaveric (15) measurements between its parts and surrounding neuroanatomical structures in all three cranial fossae. The length of the left and right lesser wings was on average 4.2 and 4 cm, respectively. The mean widths of this bony part at its midline, midpoint, and lateral point (crista alaris) were 1.5 cm, 2.0 cm, and 2 mm, respectively. From the crista alaris the mean distances to the crista galli, V3 at its exit through the foramen ovale, entrance of the occulomotor nerve into the cavernous sinus, middle meningeal artery at its emergence from the foramen spinosum, and the facial and vestibulocochlear nerves at the internal auditory meatus were 4.9, 4.5, 5, 4.7, and 6.1 cm, respectively. From the midpoint of the lesser wing, the mean distances to the crista galli, V3 at its exit through the foramen ovale, entrance of the occulomotor nerve into the cavernous sinus, middle meningeal artery at its emergence from the foramen spinosum, and the facial and vestibulocochlear nerves at the internal auditory meatus were 4.2, 2.9, 3, 3.4, and 4.7 cm, respectively. From the anterior clinoid process of the lesser wing, the mean distances to the crista galli, V3 at its exit through the foramen ovale, entrance of the oculomotor nerve into the cavernous sinus, middle meningeal artery at its emergence from the foramen spinosum, and the facial and vestibulocochlear nerves at the internal auditory meatus were 4.3, 2.8, 1, 3.3, and 4.1 cm, respectively. Additional measurements between the parts of the sphenoid ridge and surrounding anatomical structures may assist the surgeon who operates in this region or the clinician who view imaging of this anatomy.