RESUMO
OBJECTIVE: During anterior clinoidectomy for aneurysms of ophthalmic artery or paraclinoidal lesions, not only optic nerve but also cranial nerves passing through the superior orbital fissure (SOF) can be damaged by mechanical or thermal injury. Particularly, revision for paraclinoidal lesions can give further damage to the cranial nerves because of the obscure anatomical structure resulting from the tight fibrous adhesion. Thus, to reduce the damage of the cranial nerves passing through the SOF during the anterior clinoidectomy or optic canal decompression via the extradural or intradural route, morphometric relationship of juxta-clinoidal cranial nerves were studied. MATERIALS AND METHODS: Using 15 adult formalin fixed cadavers, the anatomical landmarks for measurements were chosen as follows: lateral entry point of optic nerve into the optic canal (LON), tip of anterior clinoid process (ACP), tip of posterior clinoid process (PCP), upper border of lesser wing of sphenoid bone, and lateral end of SOF. The measurements were carried out as follows: 1) distance from the LON to the dural entry point (DEP) of the third (III), fourth (IV), and ophthalmic branch of the fifth (V1) nerves into the tentorium, 2) distance from the tip of PCP to the DEP of III and VI cranial nerves, 3) distance from the LON to the cranial nerves within intradural space before passing through SOF, 4) The shortest depth from the tip of ACP and the edge of lesser wing to the cranial nerves passing through the cavernous sinus, 5) distance from the lateral end of SOF to the cranial nerves just before passing through the annular tendon. RESULTS: The mean distance from the LON to the DEP of the III, IV, and V1 cranial nerves were 10.4 mm, 18.8 mm, and 23.4 mm, respectively. The mean distance from the tip of PCP to the DEP of the III and VI cranial nerves were 5.4 mm and 18.6 mm, respectively. DEP of the III cranial nerve was corresponded with the just anterior coronal plane of PCP. The mean distance from the LON to the III, IV, and V1 cranial nerves passing through the SOF were 7.2 mm, 10.0 mm, 10.5 mm and 10.6 mm, respectively. The III cranial nerve located at a mean depth of 3.4 mm from the tip of ACP. The IV, V1 , and VI cranial nerves located at a mean depth of 2.1 mm, 2.4 mm and 7.4 mm from the upper border of lesser wing of sphenoid bone, respectively. The III cranial nerve splitted into superior and inferior divisions at a mean distance of 1.51 mm from the lateral end of SOF, just before where it passes through the SOF. The mean distance from the lateral end of SOF to the lateral margins of the III, IV and frontal nerves of V1 were 12.5 mm, 11.0 mm and 10.2 mm, respectively. CONCLUSION: DEP of the III cranial nerve was corresponded with the just anterior coronal plane of PCP and was about a half distance from PCP than from LOP. DEP of the IV cranial nerve looks like same site as that of V1 cranial nerve, but IV cranial nerve located at just superior to V1. From the LON, III, IV, V1 , and VI CNs latero-inferiorly passed through the SOF. The III cranial nerve located at the most medial portion of SOF with a mean distance of 7 mm, and the IV, V1 and VI cranial nerves were arranged in the same order as vertical arrangement with a mean distance of 10 mm. The cranial nerves just before passing through SOF were located at a range of 7.8 to 20 mm from the lateral end of SOF. This study facilitates an understanding of the anatomy of juxta-sellar region and may help to reduce the cranial nerve injury at the surgery around juxta-clinoidal CNs.