Microsurgical Anatomy And Operative Approaches Of The Region Of The Tentorial Incisura

Part IMicrosurgical Anatomy of the Middle Incisural Space of the Region of the Tentorial IncisuraObjectiveTo study the neural, cisternal, ventricular, arterial and venous relationship of the middle incisural space of the region of the tentorial incisura, as well as the cranial nerves and tentorial artery. To search the anatomical landmarks of these important neurovascular structures. Materials and methodsTwenty adult cadaveric heads were examined using ×6 to ×40 magnification after perfusing the arteries and veins with colored latex. In each, the relationship of the neural structures, cisterns, ventricles, arteries, veins and the tentorial artery were observed. The distances separating the important neursovascular structures and landmards were measured. ResultsThe important cranial nerves related to the middle incisural space of the tentorial incisura are the oculomoter, the trochlear and the trigeminal nerves. And the important arteries related to the middle incisural space are the anterior choroidal, posterior cerebral and superior cerebellar arteries. Superior cerebellar artery, the medial posterior choroidal artery and the long circumflex branches of posterior cerebral artery course middle incisural space parallel to the posterior cerebral artery. The important veins in this region is basal vein. The entrance site of oculomotor nerve to the roof of the cavernous sinus located at 11.2 ± 4.3mm posterior to the anterior clinoid process, 4.4 ± 1.4mm laterally posterior to the posterior clinoid process. The entrance site of trochlear nerver located at 23.3 ± 3.0mm posterior to anteriorclinoid process, 14.5 ± 3.9mm laterally posterior to the posterior clinoid process. The entrance site of oculomotor nerver located at 6.3 ± 1.6mm posterior to the sheath of internal carotid artery, while entrance site of the trochlear nerve 17.9 ± 3.5 to the sheath of internal carotid artery. The entrance site of trochlear nerve located at 17.9 ± 3.5mm posterior to the entrance site of oculomotor nerve. Before entering the cavernous sinus, one part of the trochlear never courses the middle incisura space 1.9 ± 0.4mm medial to the free edge of the tentorium. Superior cerebellar artery usually passes below the level of the free edge with the distance 5.1 ± 2.3mm away from the level of the free edge. The main trunk of the posterior cerebral artery is usually 3.3 ± 1.7mm higher than the level of the free edge. The tentorial artery (Bernasconi-Cassinari artery) is existed at the 90% of the total cadaveric heads. In four sides of the specimens, besides the meningohypophyseal trunk, the artery that supplies the tentorium is also aring from the posterior cerebral artery.ConclusionsAnterior clinoid and posterior clinoid process - the two main points that construct the oculomotor trigone are the important landmarks for the surrounding important neurovasuclar structures. The sheath of internal carotid artery is also the landmark for the entrance site of the oculomotor and trochlear nerve. In the middle incisural space of the region of the tentorial incisura, the trochlear nerve is usually hided under the free edge of the tentorium. Then it should be very cautious when incising the tentorium. Besides the anterior and posterior clinoid process, the entrance site of the oculomotor can be used as the lankmark for the entrance site of the trochlear nerve during operation. The superior cerebellar artery, the posterior cerebral artery with its important branches, which are the medial posterior choroidal artery and the long circumflex branch are all closely related to the middle incisural space, and should not be injured during operation. The tentorial artery (Bernasconi-Cassinari artery) is still the major artery that supplies the tentorium. There are varied origins for the arteries that supply the tentorium.