ABSTRACT
The present study has been undertaken to investigate the ultrastructure of the dura mater so as to correlate its structure with its mechanical function. This study aimed also to contribute further to the understanding of the functional morphology of the barrier formed by the mesothelial lining of the arachnoid mater to find a satisfactory explanation of the mechanism of bulk outflow of cerebrospinal fluid from the subarachnoid space into the dural sinuses. The clinical implication of this study in lumbar puncture procedure is also discussed. Six young adult sheep, eight rats, and four monkeys were used in this study. Specimens of 7 human lumbar dura and arachnoid were obtained during surgical treatment of disc herniation. Dura and arachnoid specimens were prepared for light and electron microscopy. Human Lumbar dura mater is divided into three parts: outer, middle and inner. In the outer part of the dura, collagen appears to be running in a longitudimal direction. Few elastic fibers and nerve fibers are also present. In the middle part, the collagen fibers are arranged in various directions with few elastic fibers in between. The inner part is less dense with collagen running mainly in a longitudinal direction. Numerous fibroblasts are present. The outer arachnoid is lined by a single layer of mesothelial cells. Below this are dark cells. The inner spinal human arachnoid is composed of groups of clear cells As regards spinal dura and arachnoid in the sheep, collagen fibers appear, in the outer dura, to be running in a longitudinal direction. In the middle dura, collagen is arranged in various directions. The inner dura is composed of collagen fibers running longitudinally and obliquely. Dark and light cells are present in the arachnoid. The collagen in the rat's dura is running mainly in a longitudinal direction in the outer part of the dura and in various directions in the inner part. The dural-arachnoid interface is readily identified by the presence of electron-dense granular material. At places, the arachnoid cells approximate that dense band thus diminishing the subdural space. The arachnoid is composed of fibrous connective tissue with numerous trabeculae. The arachnoid dark cells are characterized by dark nuclei with abundant heterochromatin. The dura of the monkey is composed of dense fibrous connective tissue consisting of collagen bundles and fibroblasts. The inner dura is highly cellular containing elongated fibroblasts. The collagen is loosely arranged in the inner dura. The subdural space is observed at the dural arachnoid interface in places however, this space was obliterated by the close approximation of the dural and arachnoid walls. The arachnoid is composed of two types of cells, clear and dark. The dura is composed of dense flbroblastic connective tissue and the collagen fibers are its major structural component. They have the strongest mechanical properties. Thus, the orientation of collagen fibers may explain the mechanical properties observed in different tissues. It has been previously indicated that the collagen fibers are arranged in a longitudinal and this explains the strong mechanical properties of the dura when subjected to stretching and deforming forces during movements and postural changes. Hopefully, increased understanding may open the way for new approaches in the evaluation of dural lesions produced by different needle bevels and the relationship of dural lesions to the production of postural headache