Meninges

The brain and spinal cord are covered with three membranes: (a) the dura mater, a thick outer fibrous membrane, containing large venous sinuses and separating the cranial cavity into a supratentorial and an infraten-torial compartment; (b) the arachnoid, beneath the dura, a thin avascular membrane covered with mesothe-lial cells; the arachnoid villi (granulations) are tufts of arachnoidal (meningothelial) cells that project into the venous sinuses and veins; and (c) the pia mater, a thin, inner fibrous membrane attached to the surface of the brain and spinal cord and connected to the arachnoid by delicate fibrous trabeculae. The arachnoid and the pia together form the leptomeninges. Between them is the subarachnoid space, filled with cerebrospinal fluid (CSF). The CSF is absorbed into the venous sinuses at the arachnoid villi. The pia mater contains blood vessels, accompanying them into the neural parenchyma and forming the perivascular or Virchow-Robin spaces filled with CSF. The Virchow-Robin spaces usually end at the

FIGURE 2.1 1

Meninges. A. Schematic drawing of the anatomic relationship between the dura, arachnoid, and pia. B. Leptomen-ingeal carcinomatosis extends into the cerebral cortex along the Virchow-Robin spaces (HE).

FIGURE 2.1 1

Meninges. A. Schematic drawing of the anatomic relationship between the dura, arachnoid, and pia. B. Leptomen-ingeal carcinomatosis extends into the cerebral cortex along the Virchow-Robin spaces (HE).

Pia Mater kull ura Arachnoid

Pia Mater kull ura Arachnoid

level of transition of arterioles to capillaries. They provide a route for the extension of inflammation or neoplasm from the subarachnoid space into the parenchyma (Fig. 2.11).

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