Anatomical Observation Of Opticocarotid Space Through Pterional Approach

Objectives: To dissect the four surgical spaces around saddle area via the simulation of pterion approach,carefully observe and measure the second space especially.Describe the relations of the second space with surrounding nerves and vessels,and also the fields at different angles of operational view.The angle between internal carotid artery and optic nerve will be measured as well as the side length value of the second space.This study may provide useful data for the operations that across the second space via pterion approach.Methods: The simulative craniotomy via pterional approach was deployed on 7 cadaveric head(14 sides).The cadaveric head was fixed on the operational desk via a head holder.The position was kept as leaned back with 10° and rotated toward the contralateral side with 30°,which was deployed to make sure the zygomatic process was placed in the highest position.A curve skin incision was made from 1.0cm in front of the tragus and 0.5cm above the zygomatic arch,and ended at the middle line.During this procedure,the trunk of the superficial temporal artery was protected.The scalp was dissociated and turned over.Make sure close to the temporalis intrinsic fascia when dissociate around the temporalis area.Then turn the sclap together with the superficial temporal fascia and galea aponeurotica to the temporal side to insure that the frontal branch of facial nerve was intact.The flap was dissociated until the zygomatic process of frontal bone and the superior border of the zygomatic arch were exposed.The temporalis muscle and fascia was cut through around the zygomatic process of frontal bone and the superior border of the zygomatic arch.Dissociating and retracting the temproralis muscle backward in order to expose the skull adequately.Then the first bone hole,which was also named as the key hole,was drilled on the zygomatic process of frontal bone using an electric drill.The following bone hole was drilled on the parietal bone posterior the coronal suture as the second and on the squamous bone as the third respectively.The bone flap was milled by an electric milling cutter and the sphenoid ridge was removed by rongeur to get to the anterior cranial fossa level,which could relieve the retraction of the frontal lobe during the operation.Cutting and fixing the dura,then dissociating the sylvian cistern,carotid cistern,optic chiasm cistern and lamina terminalis cistern under the microscope.Dissecting the anterior space of optic chiasma(space I),the opticocarotid space(space II),the space between internal carotid artery and tentorium cerebelli(space III)and the space of terminal lamina(space IV)respectively,microexamination and measuring space II especially at different view angles such as 0°,30°,60°.The length of optic nerve,internal carotid artery,and the A1 segment of anterior cerebral artery that composed space II were measured and analyzed as well as the angle of internal carotid artery and optic nerve.Results: The anterior space of the optic chiasm(space I)was composed by the interior margin of the optic nerve and the posterior margin of the sphenoid platform.The structure that could be seen through space I include: the interior side of contralateral internal carotid artery,the initial segment of ophthalmic artery and superior hypophyseal artery that close to the superior posterior of the sellae diaphragma and distributed to the optic nerve,pituitary stalk and the sellae diaphragm.The pituitary stalk and superior hypophyseal artery could be seen pass through the foramen of diaphragm sellae.When retracting the optic nerve to the ipsilateral side,the superior hypophyseal artery and its branch could be seen clearly.The opticocarotid space(space II)was composed by the optic nerve/ periphery optic chiasm,the interior of the supraclinoid carotid artery and the A1 segment of the anterior cerebral artery.The conformation and size of space II was determinated by the tortuosity of the internal carotid artery and the level of the internal carotid artery bifurcation.The length of the same side was also variable when was seen at different view angles.The length of the interior edge(ab)was 6±2.2mm,7.2±2.0mm,7.9mm±2.3mm,when was observed at 0°,30° and 60° respectively.The length of the lateral edge(ac)was 6.3±2.0mm,7.5±2.1mm,8.0mm±2.2mm,when was seen at 0°,30° and 60° respectively.The length of the bottom edge(bc)was 4.3±2.1mm,3.2±1.8mm,2.7mm±2.0mm when was seen at 0°,30° and 60°.The angles between the inner and outer sides at different angles of view were as follows: 0°,19.4±5.5°,30°,16.5±4.9°,60°,13.5±3.8°.The gap area was the largest when was seen at 30° angle.Space III was composed of the outboard of the supraclinoid carotid artery,the medial margin of the basilar part of the temporal lobe and tentorium cerebelli.The structures that could been seen from this space were as follows: the oculomotor nerve,the posterior communicating artery,the anterior choroidal artery,and LM.When the LM is dissected,the BA bifurcation and PCA could be visible.The IV operation clearance,was formed by the posterior margin of the optic chiasm,the posterior edge of the end plate,and the medial edge of the bilateral optic tracts.The bilateral anterior cerebral artery A1 segment,the anterior communicating artery and the Heubner recurrent artery with its perforating branches could be seen under the microscope.Conclusions: The cadeveric head simulating pterional approach,microscopic pterional approach can clearly reveal the four operating spaces in the sellar region under the microscope anatomy.Under different visual angle,the exposed structures,the areas and the shapes of the four gaps are different.Neurosurgeons should grasp the four gaps of the microsurgical anatomy,improved the safety and reliability of the operation area.