| Part Ⅰ microsurgical anatomy of posterior communicating artery an its adjacent arachnoid membraneBackground:intraoperative preserve of arterial feeders of hypothalamus is utmost important for protection of hypothalamus. Although the information of arterial feeders of hypothalamus is much, there is little information on its relationship to adjacent arachnoid membranes from present literature.Objectives:to identify the microsurgical anatomical characteristics of posterior communicating artery and its adjacent arachnoid membranes.Materials and methods:10cadaveric heads perfused via internal carotid artery with red silicone were dissected under microscope. Large bilateral frontotemporal craniotomies were taken, and brains were removed piece by piece under microscope with high magnification, and with much attention paid to preserve arachnoid membrane and pial intact. Medial carotid membrane, intracarotid membrane, and Liliequist’s membrane, and perimesencephalic membrane, and posterior communicating artery, and premamillary artery were identified and photographed. Posterior communicating artery was removed and measured.Results:posterior communicating artery had2-5branches. Premamillary artery originated from the lateral wall of posterior communicating artery, and coursed posteriorly laterally. The origination of premamillary artery located5.42-15.3mm from the terminal of internal carotid, with average diameter0.64mm.18/20of the origination of premamillary artery situated anterior to the diencephalic leaf of Liliequist’s membrane. The upper limit of Liliequist’s membrane was attached to the front of mamillary body, and the lateral limit was attached to posterior communicating artery, and the lower limit was to fuse with basal membrane covering the sellar dorsum. The arachnoid sleeves enveloping pituitary stalk was formed by fusion of the diencephalic leaf of Liliequist’s membrane, medial carotid membrane and basal membrane. Perimesencephalic membrane, also called the mesencephalic leaf of Liliequist’s membrane, was extension of the diencephalic leaf of Liliequist’s membrane at the level of sellar dorsum, with the width of2-3mm, and attached to basilar artery, posterior cerebral artery and superior cerebellar artery via arachnoid trabecular, and the distance to basilar artery was3-4mm. Perimesencephalic membrane, which was3mm wide, extended laterally to adhere to oculomotor nerve, then inferior to tentorium. Intracarotid membrane was found in3sides, and its occurrence was3/20in our study. Intracarotid membrane attached medially to optic chiasm, and laterally to hippocampus, and superior to posterior communicating artery, and inferior to anterior choroids artery. The average length of Intracarotid membrane was5mm, and the average thickness was0.2mm, and the anterior and posterior borders were free. Medial carotid membrane, which was paired intracranial inner arachnoid membrane, was found to be continuous with basal membrane covering anterior clinoid process, stretched between anterior optic pathway and ipsilateral internal carotid artery, and attached to pituitary stalk posteriorly. There were two anatomical types of medial carotid membranes, one with intact outer membrane and abundant arachnoid trabecular medially, and the other with porous outer membrane and abundant arachnoid trabecular medially too.Conclusion:the anatomical characteristic of posterior communicating artery and its important branch, premammillary artery are identified. Furthermore, the anatomy of their adjacent arachnoid membranes is identified as well.Among three different types of posterior communicating arteries, premamillary arteries originate mostly from the lateral wall of posterior communicating arteries and course posterior superiorly and enter posterior perforated substance. The origination of premamillary artery is situated mostly anterior to the diencephalic leaf of Liliequist’s membrane. This may be regarded as intraoperative reference to identify premamillary artery. There is potential narrow interspace among the diencephalic leaf of Liliequist’s membrane, oculomotor nerve, the uncus and parahippocampus. Posterior communicating artery and its branches, intracarotid membrane and much arachnoid trabecular occupy this interspace. Open this narrow interspace, removal posterior clinoid process, incision of Liliequist’s membrane, open medial oculomotor triangle of cavernous sinus and division of perforator free segment of posterior communicating artery can be applied gradually to expose the lesion in prepontine and interpeduncular cisterns. Part Ⅱ microanatomical characteristic of superior hypophyseal artery and its adjacent arachnoid membraneObjectives:The purpose of this study was to review the anatomic features of superior hypophyseal artery and its adjacent arachnoid membrane, based on microsurgical dissection of cadaveric specimens.Materials and methods:10cadaveric heads perfused via internal carotid artery with red silicone were dissected under microscope. Large bilateral frontotemporal craniotomies were taken, and brains were removed piece by piece under high magnification with preserving arachnoid membrane and pial intact. The anatomical borders of superior hypophyseal artery and its adjacent arachnoid membrane were photographed. And superior hypophyseal artery was removed and measured.Results:In our study, each internal carotid branched superior hypophyseal artery. Majority of them were groups of minor arteries. Superior hypophyseal arteries supply ipsilateral optic nerves, chiasm, pituitary stalk, ipsilateral optic tract and infundibulum of hypothalamus. The average diameter of superior hypophyseal arteries was0.16-0.20mm in our study. In our study, the average distance between the origins of the first branches of superior hypophyseal arteries to the origins of ophthalmic arteries was0-2.05mm, and the average distance between the origins of the second branches of superior hypophyseal arteries to the origins of ophthalmic arteries was2.48-3.16mm.In this group of a total of10cadaveric heads, there were18medial carotid membranes in the total of20sides. Medial carotid membrane was found to be continuous with basal membrane covering anterior clinoid process, stretched between anterior optic pathway and ipsilateral internal carotid artery, and attached to pituitary stalk posteriorly. Arachnoid membrane enveloping pituitary stalk was found to be fusion of basal membrane, medial carotid membrane and the diencephalic leaf of Liliequist’s membrane. There were two types of medial carotid membranes, one with intact outer membrane, and the other with porous outer membrane.Stepwise removal of medial carotid membrane revealed superior hypophyseal artery coursed medially to medial carotid membrane and inferiorly to anterior optic pathway. Numbers of arachnoid trabecular were also found connecting superior hypophyseal artery and optic nerve and internal carotid artery.Conclusion:microanatomy of superior hypophyseal artery and its adjacent arachnoid membranes has been identified. Numerous arachnoid trabecular adhere to superior hypophyseal artery and medial carotid membrane. Consequently, gentle manipulation or sharp dissection of medial carotid membrane may be mandatory. Part Ⅲ microanatomy of hypothalamus artery and its adjacent arachnoid membraneObjectives:to review the anatomic features of hypothalamus artery and its adjacent arachnoid membrane, based on microsurgical dissection of cadaveric specimens.Materials and methods:10cadaveric heads perfused via internal carotid artery with red silicone were dissected under microscope. Large bilateral frontotemporal craniotomies were taken, and brains were removed piece by piece under high magnification with preserving arachnoid membrane and pial intact. The anatomical borders of anterior communicating artery complex and hypothalamus artery and its adjacent arachnoid membrane were photographed. And anterior communicating artery complex and hypothalamus artery were removed and measured.Results:hypothalamus artery with diameter of0.55-0.63mm, originated from posterior wall of anterior communicating artery or confluence of anterior communicating artery and A2segment of anterior cerebral artery, containing1to3branches. It coursed posteriorly and superiorly or inferiorly to enter anterior part of hypothalamus.Lateral lamina terminalis membrane attached superiorly to rectus gyrus, inferiorly to optic chiasm, laterally to olfactory membrane, and medially to medial lamina terminalis membrane. It separated lamina terminalis cistern and carotid cistern. It was very thin, incomplete and in most specimen absent.Medial lamina terminalis membrane was very thin and incomplete inner arachnoid membrane, attached anteriorly to A2segment of anterior cerebral artery, superiorly to rectus gyrus, inferiorly to optic chiasm. It was found in16/20specimen. Hypothalamus artery situated medially to medial lamina terminalis membrane and no arachnoid trabecular was found between them.Conclusion:microanatomical features of anterior communicating artery and hypothalamus artery, medial lamina terminalis membrane, lateral lamina terminalis membrane are identified. Division of medial lamina terminalis membrane may make manipulation of anterior communicating artery complex more safely and add the exposure. |
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