The meninges in human development

The brain and cranial meninges were studied in 61 serially sectioned embryos of stages 8-23. Much earlier stages than those examined by previous authors provided a more comprehensive view of meningeal development. As a result, the possible and probable sources of the cranial and spinal meninges are believed to be: (a) prechordal plate, (b) unsegmented paraxial (parachordal) mesoderm, (c) segmented paraxial (somitic) mesoderm, (d) mesectoderm (neural crest), (e) neurilemmal cells (neural crest), and (f) neural tube. Some of these sources (a, b, d) pertain to the cranial meninges, others (c, d, e) to the spinal coverings. The first of the future dural processes to develop is the tentorium cerebelli, which, at the end of the embryonic period proper, differs considerably in shape and composition from the later fetal and postnatal tentorium. The embryonic dural limiting layer (Duragrenzschicht) probably corresponds to the interface layer of the adult meninges. The appropriate literature was reviewed and summarized.     

A study on the microvasculature of the cerebellar cortex

Summary The arterial structure of the cerebellar cortex was studied by vascular stain and in diaphanized specimens after intra-arterial barium injection. A scanning electron microscope study on the corrosion cast of the arteries was also performed. Arteries distributed in the cerebellar hemisphere are classified into cortical, subcortical, and medullary arteries. The patterns of arterial distribution are similar to those in the cerebral cortex. The cortical arteries are subclassified into superficial, middle, and deep cortical branches. The superficial branches are very fine, forming capillary networks in the molecular layer. The middle cortical branches terminate in the Purkinje cell layer, by dividing into several branches extending parallel to the plane of this layer. These branches connect with capillaries in both the molecular and the granular layers. The deep cortical branches give off some collaterals along the Purkinje cell layer and terminate in the granular layer, by breaking up into capillary networks. The Purkinje cell layer is marked by arterial branches ramified from the middle and deep cortical branches and no particular dense capillary networks are formed in the Purkinje cell layer. The brains of older patients show intertwining of the middle and deep cortical branches, some forming rope-like appearance. These patterns are similar to those seen in the cerebral cortex, but they were found, in older people, in the cerebrum.Supported in part by a grant from the Ministry of Education, Science and Culture, Japan     

Microvasculature of the human cerebral meninges

In the present study, the human cerebral meninges were rich in blood vessels, but no capillaries were noted. The meningeal arteries ran over the veins where they crossed. Several arterial anastomoses existed on the cortical surface. The meningeal arteries were classified into four parts; the conducting artery approximately 700 µm in diameter, distributing artery approximately 200 µm in diameter, precortical artery approximately 60 µm in diameter and cortical artery approximately 30–40 µm in diameter. A single distributing artery supplied the area of approximately 3.5 × 2.0 mm on the brain surface. They further ramified into precortical arteries which stemmed cortical arteries. These precortical arteries had the distributing area of 1 mm² and this distributing area was the same size as the width of human ocular dominant column of the visual cortex. Constriction, like a sphincter, was observed at the bifurcation of the distributing arteries. The cerebral blood vessels, which regulated the blood flow and reacted to autonomic nerve stimuli, seemed to correspond to the distributing arteries.     

The microvasculature of the spinal cord in the human adult

The microvasculature of the human spinal cord have been studied with scanning electron microscopy (SEM) on the corrosion casts of blood vessels, and light microscopy on the transparent after intra-arterial injection of Indian ink and vascular staining specimens. On the surface of the cord, the density of the pial venous plexus was higher than the pial arterial plexus. The anterior spinal artery and vein gave off central arteries and veins, which ran posteriorly within the anterior median fissure. The number of the central arteries and veins per centimeter in length is highest in the lumbosacral cord, followed by the cervical and then the thoracic cord. In this study, the central arteries and veins were classified into types; type 1 dominated the arterial system and type 2 the venous system. The central arteries and veins sent long branches both rostrally and caudally along the axis of spinal cord. The order of their length was as follows: thoracic, cervical, lumbar and sacral cord. These blood vessels overlapped each other. The peripheral arteries terminated in the periphery of the gray matter while the peripheral veins originated within the different depth of the gray matter. The posterior spinal artery supplied the posterior horn and the substantia gelatinosa. The posteromedial veins arose in the deep posterior horns and posterior funiculus, and were occasionally connected with the anterior spinal vein within the cord. Overlapped zone which was supplied by both the central and peripheral vascular system was seen within the cord, and its extent was variable at different levels. The overlapped zone of the venous supply was broader than the arterial one. The peripheral veins appeared to drain blood not only from the white matter but also from the gray matter. The distribution of the capillary networks in the gray matter was slightly denser and showed more horizontal arrangement in the lumbosacral cord, and more sparse and longitudinal in the cervicothoracic cord. The distribution of the capillary networks in the white matter was parallel to nerve fibers which run longitudinal in the whole cord. Based on the result of present study, it was considered that the circulatory disturbances are prone to occur in the thoracic cord, and the circulatory block in the arterial system of the cord tends to cause a lesion in the gray matter, whereas the circulatory disturbances in the venous system tends to cause a lesion in the white matter.     

The vascularization of the human cerebellar cortex

The blood vessels of the cerebellar cortex were studied by two methods of injection: india-ink and low viscosity resin (Mercox). The study is divided into two parts: (a) Pial vessels; few in number at the cerebellar surface, the pial vessels are quite dense, forming vascular laminae, within the sulci. Pial vessels do not frequently anastomose. (b) Intracortical vessels closely resemble those of the cerebral cortex. They may be divided into three categories: short, middle and long. There exist three vascular layers within the cerebellar cortex: superficial, middle and deep. The superficial vascular layer is situated within the molecular layer, the middle within the Purkinje cell layer, and the deep within the granular layer. It is therefore possible to establish a correlation between these vascular layers and the cortical cytoarchitecture. We accorded particular attention to the vascularization of the Purkinje cells. Arteries parallel to the cerebellar surface (parallel arteries) are in close relationship to the Purkinje cells whereas capillaries and veins are scarce. It is highly probable that the majority of Purkinje cells obtain nutritive elements by these parallel arteries. Possible implications in physiology and pathology are subsequently discussed.     

Development of the meninges of the human embryonic optic nerve

From 8 to 14 weeks post-conception the human embryonic optic nerve is surrounded by loosely packed layers of connective tissue. From 8 weeks onwards the innermost layers of this sheath consist of fibroblast-like cells whereas the cells of the middle and outer layers, although similar in appearance, contain increasing amounts of glycogen, until by 14 weeks very large amounts of glycogen are present in these cells. A collagen-rich dural layer first appears at 15 weeks post-conception. This layer contains few cells. The outer-most cells have the appearance of fibroblasts and are joined to each other by long sheet-like processes. Cell in the middle of the dura are glycogen-containing cells, apparently actively engaged in collagen production. These cells are similar to those found in the adjacent arachnoid. By 18 weeks of age the meninges are well-differentiated. The endothelial cells of all capillaries found in the meninges from 8 weeks post-conception, including dural capillaries, are sealed by zonulae occludentes. At 15 and 18 weeks a few fenestrated capillaries were observed at the junction of the dura and the surrounding loose connective tissue. Peripheral nerves are closely related to the meninges from 8 weeks post-conception and peripheral nerve bundles are present in the dura from 15 weeks. At 18 weeks the first signs of myelination were observed in these bundles.     

人体皮肤微血管构筑的三维可视化*

背景：常用的血管解剖学研究方法如逐层解剖、血管染色、造影摄片可以确定血管的位置、大至供血范围等,但难以显示皮肤微血管立体构筑。 目的：建立三维的皮肤微血管构筑模型,以评估和设计穿支皮瓣。 方法：选取2具新鲜成人尸体标本,以羧甲基纤维素明胶氧化铅灌注标识血管,CT扫描获取标本灌注前后及剥离皮肤序列图像数据,利用Mimics13.1软件进行皮肤微血管三维重建和穿支皮瓣设计。 结果与结论：实验成功重建了骨骼、血管、皮肤三维数字模型,并选择性设计了旋股外侧动脉皮瓣和旋肱后动脉的主要穿支皮瓣。构建的皮肤微血管模型不仅可显示皮穿支的长度管径、立体位置、走行方向、分布范围、毗邻关系,还可追踪其来源血管,与来源血管、骨骼、皮肤等搭配显示。说明皮肤微血管构筑可揭示穿支皮瓣的范围和扩张方向,有利于穿支皮瓣的设计发掘、血供评估。     

The growth and development of microvasculature in human cerebral cortex

Sections of the occipital cortex from 31 fetuses, infants and children, ranging in age from 15 weeks gestation to ten years postnatal, were stained to demonstrate alkaline phosphatase activity in intracortical vessels. At 15 weeks gestation intracortical positively staining vessels, assumed to be arterial precursors, were radially oriented, originating from leptomeningeal arteries. Most radial vessels coursed through the cerebral cortex without branching to vascularize the subcortical tissue. By 20 weeks gestation horizontal branches arose from radial vessels, most frequently in the lower half of the cortex. Occasionally, recurrent collaterals ascended from these horizontal branches to more superficial cortex. From 20-27 weeks gestation, the number of horizontal branches and recurrent collaterals increased in the lower half of the cortex, horizontal branches appeared in the upper half. From 27 weeks to term, shorter radial vessels, terminating in the more superficial cortical laminae increased in number. After birth a network of fine vessels, presumable precursors of capillaries, increased, particularly vascular layer 3 (neuronal lamina IV and Va). The number of radially oriented vessels per mm2 of pial surface (NA) decreased throughout development, with the most dramatic decrease occurring prenatally. In five cases of trisomy values of NA decreased less rapidly than in the normal.     

Lymphatic capillaries in the meninges of the human optic nerve.

OBJECTIVE: Although many anatomical studies of the orbit and the optic nerve have been performed, lymphatic capillaries in the dura of the human optic nerve have never been reported. This study was performed to determine whether or not lymphatic capillaries are present in the dura of the human optic nerve. MATERIALS AND METHODS: This postmortem study was carried out in seven subjects without ocular disease. The subjects were obtained no later than 6 hours after death, following qualified consent for autopsy. The dura of the human optic nerve was studied with light microscopy, scanning electron microscopy, and transmission electron microscopy. In some cases, india ink was injected into the subarachnoid space as a marker. RESULTS: Lymphatic capillaries in the dura of the human optic nerve were morphologically demonstrated with histological criteria (fenestrated endothelium, lack of a basal membrane, and absence of blood cells in the lumen of the vessels). The highest concentration of lymphatic capillaries was found in the bulbar part of the dura behind the ocular globe. Using light microscopy and transmission electron microscopy, ink was seen within the lumen of the lymphatic capillaries. The dura itself was not stained with the marker. CONCLUSION: The presence of lymphatic capillaries in the dura of the human optic nerve was demonstrated with light microscopy, transmission electron microscopy, and scanning electron microscopy.     

Chondrosarcoma of the meninges

Summary A case of chondrosarcoma of the meninges in a 32 year old male is reported.     

Reduced thrombomodulin in human peripheral nerve microvasculature

Thrombomodulin (TM), a vascular endothelial receptor, terminates the actions of thrombin and accelerates activated protein C formation. TM is ubiquitous throughout the systemic microcirculation but is reduced in brain regions predisposed to lacunar infarction. We investigated whether TM is present within human nerve and differentially expressed according to vessel caliber and proximity to the blood-nerve barrier. Vascular endothelial TM was detected on sural nerve biopsies with immunohistochemistry. The proportion of TM-positive microvessels was expressed relative to total von Willebrand factor (vWF)-positive vessels. Although vWF was detectable in all microvessels, TM expression was absent from the perineurial vessels. TM was detected in 47% (15-80%, 95% confidence level) of larger epineurial arterioles, in 43% (30-61%) of smaller epineurial vessels, and in 30% (19-47%) of endoneurial vessels. These findings demonstrate that TM is present in human nerve microvasculature but is regionally deficient in proximity to the blood-nerve barrier, which may predispose nerve to microvascular ischemia in inflammatory/prothrombotic conditions.     

Presence of SSAO in human and bovine meninges and microvessels

In spite that SSAO enzyme is widely distributed in almost all tissues, specially in vascularized ones, its presence in brain microvessels is still controversy. Our results resolve this question showing that both human and bovine cerebrovascular tissues do contain the SSAO enzyme. This was achieved biochemically, using benzylamine and methylamine as substrates, and by immunoblot analysis, using polyclonal antibodies anti-SSAO that recognized a 100 kDa single band in tissue homogenates.     

Marijuana alters the human cerebellar clock

The effects of marijuana on brain perfusion and internal timing were assessed using [15O] water PET in occasional and chronic users. Twelve volunteers who smoked marijuana recreationally about once weekly, and 12 volunteers who smoked daily for a number of years performed a self-paced counting task during PET imaging, before and after smoking marijuana and placebo cigarettes. Smoking marijuana increased rCBF in the ventral forebrain and cerebellar cortex in both groups, but resulted in significantly less frontal lobe activation in chronic users. Counting rate increased after smoking marijuana in both groups, as did a behavioral measure of self-paced tapping, and both increases correlated with rCBF in the cerebellum. Smoking marijuana appears to accelerate a cerebellar clock altering self-paced behaviors.     

Cytokeratin expression in human spinal meninges and ependymal cells.

The expression of intermediate filament protein in human spinal cord arachnoid cells and ependyma was studied by immunohistochemistry and immunoblotting. Monoclonal antibodies specific for individual cytokeratin polypeptides indicated a developmental change in the presence of cytokeratin 8 and 18 in spinal leptomeninx and tanycytes of the spinal cord ependyma. While in fetal material cytokeratin 8 and 18 were abundant in arachnoid cells, in adults immunoreactivity was restricted to a few cells. Immunoblots prepared from adult as well as fetal arachnoid membranes showed significant amounts of cytokeratin 8. These findings indicate that although cytokeratin is represented in both fetal and adult arachnoid cells there is development regulation of its specific localization.     

Ultrastructural parameters of limbic microvasculature in human psychomotor epilepsy

Temporal lobe tissues from seven patients with drug refractory complex partial seizures were extensively examined using both light and electron microscopy in combination with certain computer techniques. Four of these cases had mesial sclerosis, whereas three cases had no demonstrable lesions in the hippocampus as determined by intermittent serial sections. Transverse sections of hippocampus were made and rapidly fixed in the operating theatre. Blocks were taken after orientation to a close-up photograph of the fixed unstained hippocampus. Cross sections of capillaries at a level where the nuclear outline was largest were photographed at low magnification in the electron microscope. Enlarged prints allowed the use of a computer-assisted planimetry and stereology system for determining capillary thickness, mean basal laminar thickness, mitochondrial incidence, and mitochondrial area of both endothelial and perithelial cells and numbers of light junctions occurring in the capillaries. Comparison of sclerotic tissues versus control showed a significant increase in laminar thickness of the sclerotic endothelia and perithelia. In endothelial cells of the disordered cortex there were fewer mitochondria than in controls; also these same endothelial cells had greater numbers of tight junctions. These changes are related to ongoing hippocampal neuron degeneration, dysregulations of the blood-brain barrier because of possible resistance to perfusion, and interference with transcapillary transport in relation to [K+] levels in neuronal milieu.     

Primary malignant melanoma of the meninges

A case of primary malignant melanoma of the meninges is described in which the clinical presentation is that of visual loss and limb weakness. Clinically a diagnosis of carcinomatous meningitis was made and subsequently malignant cells were found in the cerebrospinal fluid (CSF). At autopsy the diagnosis of primary malignant melanoma of the meninges was made.     

Solitary fibrous tumor of the meninges

Intracranial fibrous tumors are unusual growths that occur almost exclusively in young individuals. Most of these lesions are intra-axial, however, on extremely rare occasions they arise from the leptomeninges and compress the adjacent brain. The authors report the case of a benign solitary fibrous tumor of the meninges in a 14-year-old girl who presented with a 5-month history of generalized headaches. NMR imaging displayed a left parietal mass, which mimicked a meningioma.