Meninges & Cisterns PDF

Meninges & Cisterns Prof Dara M Cannon Meninges • The meninges are the layers surrounding the brain, inside the skull that provide attachments and fluid filled spaces for protection of the brain and spinal cord Different layers of the meninges • Coverings of the brain that lie immediately deep to...

Meninges & Cisterns Prof Dara M Cannon Meninges • The meninges are the layers surrounding the brain, inside the skull that provide attachments and fluid filled spaces for protection of the brain and spinal cord Different layers of the meninges • Coverings of the brain that lie immediately deep to the cranium • Protect and enclose the brain and spinal cord in a fluid filled cavity • Provide a framework for vessels: arteries, veins and venous sinuses A fold of one of the layers, separating the cerebral hemispheres Objectives • To describe and be able to identify the anatomical location, structure, folds and features of the coverings of the CNS as well as their anatomical relations, spaces, contents and the significance of those features Meninges – Layers • Composed of three connective tissue layers • Dura mater • thick external fibrous layer, tough • Arachnoid mater • Thin intermediate layer Dura • Pia mater Dura • Delicate internal vascular layer Dura Mater • Periosteal layer (periosteum) covers and adheres to the internal cranium surface • Meningeal layer is a strong fibrous membrane that is continuous at the foramen magnum with the dura covering the spinal cord (one layer of dura) • These layers fold which results in incomplete dividers between brain regions and spaces such as the venous sinuses • Meningeal arteries and veins (anterior, middle and posterior) • Trigeminal (CN V) branches innervate the dura mater Arachnoid & Pia Mater • Continuous with one another, leptomeninx • Arachnoid avasular • Pia highly vascularized • Form the subarachnoid space between them: CSF • Arachnoid (web-like) trabeculae traverse the space • Arachnoid granulations • Collections of arachnoid villi • Protrude through the meningeal layer of the dura • Pass CSF into the venous blood system • Pia is a thin membrane adheres to the surface of the brain Meninges – Spaces • Epidural / Extradural • Not a natural space between the cranium and the periosteal layer of the dura • Tightly adhered to cranium • Subdural • Between the meningeal layer of the dura and the arachnoid mater, not a natural space • No attachments, CSF pressure usually keeps arachnoid mater against the dura • Subarachnoid (SA) space • A real space between the arachnoid and the pia mater, contains CSF, trabecular cells, cerebral arteries, bridging veins • Cisterns, expanded areas of SA space: quadrigeminal, cisterna magna Cisterns • Cisterns are subarachnoid spaces filled with CSF Bleeding (Haemorrhage or Stroke) into the Meningeal Spaces Folds of Dura Dura • Note the attachments in the lab • The meningeal layer folds on itself to form dividers • One lies between the two hemispheres of the brain – this one is therefore sagittal in orientation • Another divides the space containing the cerebrum from that containing the cerebellum it is more horizontal in orientation Dura • Periosteal layer attaches firmly to the skull Folds of Dura • Falx cerebri • Largest, separates the hemispheres of the cerebrum • Tentorium cerebelli • • • Separates the cerebrum from the cerebellum Tentorial notch, brainstem passes through this space Supratentorial and infratentorial e.g. tumors Most childhood tumors are infratentorial, while most adult tumors are supratentorial. • Falx cerebelli • Separates right and left cerebellar hemispheres • Diaphragma sellae • Smallest, covers clinoid processes and folds around pituitary gland Posterior Brainstem Identify the Folds of Dura C This is a key to show you the level of each of the CT slices A through E in these axial images • For your clinical interest, have a look at a condition called Petalia: Cerebral dominance and asymmetry of the dural partitions E is a key to show you the level of each of the CT slices A through D in these coronal images Check your knowledge using these questions • Meninges • • • • How many layers are there, do some have sublayers? Can you name them in order of superficial to deep? Between which specifically do the venous sinuses lie? What do the venous sinuses carry, can you name each region on the route of the venous sinus system back to the heart? • Can you name the spaces, from superficial to deep relative to each layer from superficial to deep? • What does each space contain if anything? Test yourself Test yourself For your clinical interest, have a look at a condition called Petalia: Cerebral dominance and asymmetry of the dural partitions