Meninges | Brain Parts

Meninges

Ashley Davidoff MD

Definition

The meninges represent the outer covering of the consisting of three layers; duramater pia mater and the arachnoid.

The meninges contain the brain and the meninges themselves are secured in position through attachments with the skull. During movement of the head and body, the brain is protected from moderate degrees of acceleration/deceleration injury. They function to secure the shape and situation of the brain and its components.

The duramater (meaning hard mother) is the outer most layer and it also forms the falx cerebri

The arachnoid (meaning spider like since it contains many small vessels)is middle layer and assists in the circulation of the CSF

The pia mater (meaning delicate mother) is a delicate membrane that is intimately adherent to the brain.

arachnoid villi produce CSF reabsorbed through dural sinuses

General Organization of the Meninges

The coronal drawing reveals the three layers of the brain. The inner layer (maroon) is the pia mater and it is in intimate contact with the brain and faithfully follows the sulci and gyri. The second layer is the arachnoid (pink) which is a slightly thicker membrane and follows the pia in a general fashion but does not extend into the sulci. It is intimately attached to the inner layer of the dura (bright green) The space between the pia and the arachnoid is the subarachnoid space, and it is in this space that the CSF is present and surrounds the brain. The next layer is the dura which is a double layer. The inner layer (bright green) is intimately attached to the arachnoid and the outer layer (also bright green) is attached to the bone and functions as the inner periosteum. There is a potential space between the arachnoid (pink) and the inner layer of the dura (green). This space is called the subdural space. (combination pink and green) The CSF (light blue) is seen in the subarachnoid space and in the lateral ventricles (gray blue)

The Piamater, Subarachnoid Space, and the Arachnoid

The histological section of the cortex at 10X magnification reveals two of the three meninges of the brain. The inner layer (maroon) is the pia mater and it is in intimate contact with the brain and faithfully follows the sulci and gyri. At this magnification it is barely visible since it is very thin. The second layer is the arachnoid (pink) which is a slightly thicker membrane and follows the pia in a general fashion but does not extend into the sulci. It is intimately attached to the inner layer of the dura The space between the pia and the arachnoid is the subarachnoid space, and it is in this space that the CSF is present and surrounds the brain. A small blood vessel likely a vein is seen entering the brain via the subarachnoid space.

Image Courtesy of Thomas W.Smith, MD; Department of Pathology, University of Massachusetts Medical School. 97377b04.9

Dura and Arachnoid and Subarachnoid Space

MRI T1 Weighted Coronal View

The coronal T1 weighted MRI reveals demonstrates some of the anatomical features of the meninges and their relations The sulci are seen as T1 dark CSF containing fissures in the brain substance. The pia is too thin to see but would be adherent to the brain surface. The space that contains the CSF is called the subarachnoid space (light blue). The very fine T2 bright membrane seen on the surface of the brain is a combination of arachnoid (pink) adherent to the two layers of the dura (green). The outer layer of the dura acts as the inner periosteum and is adherent to the skull. The dura splits at the vertex to encompass the superior sagittal sinus and then extends down in the interhemispheric fissure to form the falx. The thin black T1 dark layer after the arachnoid and dura is the inner cortical bone, and is followed by the T1 bright fat containing marrow of the skull. Next is the thin black T1 dark outer cortical bone, followed by a thick layer of T1 bright subcutaneous fat, and then a thin layer of isointense (to soft tissue) skin layer.

Dura and Arachnoid and Subarachnoid Space

MRI T1 Weighted Coronal View

The coronal image of the brain using T1 weighted MRI sequence reveals the three layers of the brain. The inner layer (maroon) is the pia mater and it is in intimate contact with the brain and faithfully follows the sulci and gyri. The second layer is the arachnoid (pink) which is a slightly thicker membrane and follows the pia in a general fashion but does not extend into the sulci. It is intimately attached to the inner layer of the dura (bright green) The space between the pia and the arachnoid is the subarachnoid space, and it is in this space that the CSF that surrounds the brain is housed. The next layer is the dura which is a double layer. The inner layer (bright green) is intimately attached to the arachnoid and the outer layer (also bright green) is attached to the bone and functions as the inner periosteum. There is a potential space between the two layers of the dura. The CSF (light blue) is seen in the subarachnoid space and in the lateral ventricles (gray blue)