Neuroanatomy Atlas in Clinical Context

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and Related Hemorrhages 4

Meninges, Cisterns, Ventricles,

T he meninges consist of dura mater ( pachymeninx ), arachnoid mater , and pia mater; the latter two form the leptomeninx . The meninges are composed of fibroblasts modified in different layers to serve specific functions. The outer layers, the periosteal dura and men ingeal dura , are composed of elongated fibroblasts and large amounts of collagen and have great strength. Vessels in the pachymeninx are located at the dura-skull interface generally forming indentations/grooves in the inner table of the skull. The periosteal dura forms the periosteum on the inner table of the skull, is tightly adherent to the inner table particularly at suture lines, and is located external to the dural sinuses. The meningeal dura forms the dural reflections ( falx cerebri , tentorium cerebelli , dia phragma sellae , falx cerebelli ) that are located internal to specific venous sinuses. Extradural ( epidural ) hemorrhages or hematomas are sequestered between the inner table of the skull and the periosteal dura. The innermost part of the dura, the dural border cell layer , is attached to the externally located meningeal dura and to the internally located arachnoid mater. It is made up of sinuous elongated fibroblasts separated by extracellular spaces containing an amorphous material but no collagen; this layer has markedly few cell junctions. The dural border cell layer is a structurally weak plane at the dura-arachnoid interface; so-called subdural hemor rhages or hematomas are sequestered within this layer. There are no naturally occurring spaces between the inner table and the periosteal dura or external to, within, or internal to, the dural bor der cell layer. Consequently, epidural hematoma and the so-called sub dural hematoma , with their characteristic shapes, extents, and clinical sequelae are usually the result of a traumatic or pathologic event. There is a naturally occurring spinal epidural space between the spinal dural sac and vertebral column; the vertebrae have their own periosteum.

The arachnoid mater is composed of cells that are less elongate, tightly packed with little/no extracellular space, and attached to each other by desmosomes and tight junctions. The arachnoid membrane is located internal to the dural border cell layer and, along with the menin geal dura, forms the various dural reflections . This layer is generally two to four cells thick and forms a barrier against the movement of cerebrospinal fluid (CSF), hence its designation as the arachnoid bar rier cell layer . The naturally occurring subarachnoid ( leptomeningeal ) space ( SAS ) is located between the arachnoid and pia and provides for the egress of CSF from the ventricles, circulation around the brain and spinal cord, and reabsorption into the venous system particularly at the arachnoid villi . Arachnoid cap cells generally found in the vicinity of these villi are a primary source of cells that develop into meningioma . Blood within the SAS ( subarachnoid hemorrhage ) is most commonly seen following trauma and secondarily after rupture of an intracranial aneurysm. The causative agents for bacterial or viral meningitis may be found in the leptomeningeal space. The arachnoid trabeculae are com posed of numerous elongated sinuous fibroblasts that traverse the SAS. These have cell junctions with the arachnoid layer and with the pia and may contain collagen in folds of their cell membranes. The fibroblasts forming the pia mater are adherent to the CNS sur face and follow all of its various undulations, in some places forming a single layer. Taken together the pia mater and the glial limiting mem brane (protoplasmic astrocyte cell processes at the CNS surface) form the pial-glial membrane . Occasional small subpial spaces containing collagen fibers are found at the pia-brain interface. Large vessels located in the SAS may be partially, or totally, enveloped by pial cell and/or trabecular cell processes.

Skull

Location of epidural hematoma

Periosteal dura

Dura mater

Meningeal dura

Dural border cell layer

Location of subdural hematoma

Arachnoid mater Copyright © Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. 2024 Arachnoid barrier cell layer Basement membrane SAS SAS

Arachnoid trabeculae in SAS

Position of subarachnoid hemorrhage

Subarachnoid space (SAS)

Collagen

Pia mater

Pia–glia membrane (intima pia) Occasional subpial space

Pia–glia membrane (intima pia)

Basement membrane

Brain surface

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