meningens

The meninges are a series of protective membranes that enclose the brain and spinal cord. They provide structural support, contribute to the circulation and containment of cerebrospinal fluid (CSF), and participate in immune defense of the central nervous system.

The three principal layers are the dura mater, arachnoid mater, and pia mater. The dura mater is the tough outer layer, which in the brain consists of an outer periosteal layer that lines the skull and an inner meningeal layer. The two layers form folds (such as the falx cerebri, tentorium cerebelli, and diaphragma sellae) that partition portions of the brain and create dural venous sinuses, which drain venous blood from the brain. The arachnoid mater is a delicate, web-like membrane beneath the dura. The pia mater is a thin, tightly adherent layer that closely follows the contours of the brain and spinal cord.

Between the arachnoid and pia maters is the subarachnoid space, which contains CSF and cerebral blood vessels. The subdural space, located between the dura and arachnoid, is a potential space that can become a real space in pathology. CSF circulates within the subarachnoid space and is reabsorbed into the venous system via arachnoid granulations projecting into the dural venous sinuses.

Clinical relevance includes meningitis, an inflammation of the meninges due to infection, and meningiomas, tumors originating from arachnoid cap cells. Meningitis presents with headache, fever, neck stiffness, and altered mental status, while meningiomas are typically slow-growing and may cause focal neurological symptoms depending on their location.