The fine anatomy of the human spinal meninges

A light and scanning electron microscopy study

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✓ The fine anatomy of the human spinal meninges was examined in five postmortem spinal cords taken within 12 hours after death from patients aged 15 months to 46 years. Specimens of spinal cord were viewed in transverse section and from the dorsal and ventral aspects by scanning electron microscopy. Transverse sections of spinal cord and meninges were also examined by light microscopy. The arachnoid mater was seen to be closely applied to the inner aspect of the dura. An intermediate fenestrated leptomeningeal layer was observed attached to the inner aspect of the arachnoid mater and was reflected ventrally to form a series of dorsal septa. As it arborized laterally over the surface of the cord to surround nerves and blood vessels, the intermediate layer became highly fenestrated but remained distinct from the pia and arachnoid mater.

The pia mater appeared to form a continuous layer which was reflected off the surface of the cord to coat blood vessels within the subarachnoid space in a manner similar to that described in the leptomeninges over the human cerebral cortex. Each dentate ligament consisted of a collagenous core which was continuous with the subpial connective tissue and was attached at intervals to the dura; pia-arachnoid cells coated the surface of the dentate ligaments. The present study suggests that the fine anatomy of the human spinal meninges differs significantly from that described in other mammals.

Article Information

Address reprint requests to: David S. Nicholas, M.B.,B.S., M.R.C.Path., Department of Pathology (Neuropathology), Level E, Laboratory and Pathology Block, Southampton General Hospital, Southampton SO9 4XY, England.

© AANS, except where prohibited by US copyright law.

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Figures

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    Scanning electron micrograph of the lumbar spinal cord of a 15-month-old child. An intermediate leptomeningeal layer (IL) is closely applied to the inner aspect of the arachnoid (A). It reflects to form the dorsal septum (S) and arborizes over the dorsal surface of the cord. The dentate ligaments (L) are seen on each side of the cord: that on the left merges with the dura (D). On the right, the free margin of the dentate ligament abuts upon the arachnoid mater.

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    Photomicrographs of the same spinal cord as shown in Fig. 1. H & E, × 42. Left: The dentate ligament (L) is shown crossing the subarachnoid space. The arachnoid (A) is reflected over the dentate ligament. The collagenous core is thickened laterally and fuses with the dura (D); medially it merges into the subpial collagen. Right: The free margin of the dentate ligament (L) is shown covered by a layer of leptomeningeal cells. Medially, the dentate ligament fuses with the subpial collagen (Coll).

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    Scanning electron micrograph of the thoracic spinal cord from a 45-year-old man. Toward the lower right of the picture the arachnoid (A) has become detached from the dura (D). Dentate ligaments (L) are present on each side of the cord. Septa traverse the subarachnoid space dorsally and dorsolaterally. × 3.

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    Scanning electron micrographs of the spinal cord shown in Fig. 3. × 44. Left: The fenestrated intermediate leptomeningeal layer (IL) is loosely attached to the inner aspect of the arachnoid mater (A). The dorsolateral septum (S) arises as a reflection of the intermediate layer. Right: The fenestrated dorsolateral septum is seen arborizing around dorsal nerve roots and blood vessels on the surface of the cord. COLL = subpial collagen.

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    Photomicrograph of the dorsal septum (S) from the spinal cord shown in Fig. 3. It consists of cells and collagen. The dura is shown at the top and the spinal cord at the bottom. H & E, × 130.

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    Scanning electron micrograph, dorsal view, of the thoracic spinal cord from an adult showing a series of the severed and collapsed dorsal septa (S) to the left of the midline. Arrow indicates the free margin of the septum. A smaller dorsolateral septal remnant is also present. Both dorsal and dorsolateral septa fuse with the intermediate layer (IL), which is highly fenestrated laterally, but forms a complete layer near the midline. × 12.

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    Scanning electron micrographs of the spinal cord shown in Fig. 6. Left: Magnified view of the right lateral aspect of Fig. 6 showing the intermediate leptomeningeal layer arborizing to form trabeculae. × 160. Right: View of the pia mater obtained by looking through fenestrations in the intermediate layer. Ridges in the pial surface (arrow) probably correspond to cell borders. × 3800.

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    Scanning electron micrograph, end-on view, of a transverse section of spinal cord showing the intermediate layer (IL) at the top of the picture and pia mater covering the spinal cord at the bottom. The severed end of a small blood vessel and a nerve rootlet are seen within the subarachnoid space. × 150.

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    Diagrammatic representation of the human spinal cord with surrounding meninges. The arachnoid mater (A) is closely applied to the thick outer dura (D). An intermediate leptomeningeal layer (IL) lies between the arachnoid mater and the pia mater. This layer is fenestrated and is attached to the inner aspect of the arachnoid mater. It is reflected to form the dorsal septum (S). The intermediate layer spreads over the surface of the cord and is connected to blood vessels, nerve roots, and pia mater by fine trabeculae. Dentate ligaments are present on either side of the cord and are covered by a layer of pia arachnoid. The collagenous core of the dentate ligaments fuses with subpial collagen medially and at intervals laterally with dural collagen, as shown on the left side of the diagram. Blood vessels (V) within the subarachnoid space are coated by a leptomeningeal sheath continuous with the pia mater.

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