meninges, Dural sinuses and CSF circulation.pptx

meninges, Dural sinuses and CSF circulation

1. Practical anatomy Meninges, DVS & CSF circulation Lab; C.O.A Session; 10 th session; pages; 519-582-640-645-710 References; C.O.A By Richard Snell & Frank Netters atlas

2. The meninges refer to the membranous coverings of the brain and spinal cord. There are three layers of meninges, known as the  dura mater, arachnoid mater and pia mater. These coverings have two major functions: Provide a supportive framework for the cerebral and cranial vasculature.

3. Dura Mater The dura mater is the  outermost  layer of the meninges and is located directly underneath the bones of the skull and vertebral column! . It is thick, tough, and inextensible ( non-stretchable ). The dura mater consists of two  layered  sheets of connective tissue: Periosteal layer  – lines the inner surface of the bones of the cranium. Meningeal layer  – located deep to the periosteal layer. It is continuous with the dura mater of the spinal cord. The  dural venous sinuses  are located between the two layers of dura mater. They are responsible for the venous drainage of the cranium and empty into the  internal jugular  veins. The dura mater receives its own vascular supply – primarily from the  middle meningeal  artery and vein. It is innervated by the trigeminal nerve (V1, V2 and V3).

4. Dural Reflections The meningeal layer of dura mater folds inwards upon itself to form four   dural reflections. These reflections project into the cranial cavity, dividing it into several  compartments  – each of which houses a subdivision of the brain. The four dural reflections are: Falx cerebri  – projects downwards to separate the right and left cerebral hemispheres. Tentorium cerebelli  – separates the occipital lobes from the cerebellum. It contains a space anteromedially for passage of the midbrain – the tentorial notch. Falx cerebelli  – separates the right and left cerebellar hemispheres. Diaphagma sellae  – covers the hypophysial fossa of the sphenoid bone. It contains a small opening for passage of the stalk of the pituitary gland.

5. DVS D.V.S refer to multiple venous channels within the cranial cavity, which are sandwiched between the two layers of the dura mater ( the outermost layer of the meninges ). Multiple venous channels within the cranial cavity, which are sandwiched between the two layers of the dura mater ( the outermost layer of the meninges). This venous system represents the main pathway of returning venous blood from the brain into the circulation via the  internal jugular vein .

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7. Pia mater   It is the innermost of the meninges, closely adhering to the surface of the brain and spinal cord . The term “pia mater” means “tender matter.” It is composed of delicate connective tissue and has many tiny blood vessels. The pia mater accompanies the vessels that enter the nervous tissue from the subarachnoid space, forming the outer wall of the perivascular spaces. Cerebral arteries and veins travel in the subarachnoid space, completely enveloped by pia mater.

8. Denticulate ligaments  (also known as  dentate ligaments ) are  lateral  projections of the spinal  pia mater forming triangular-shaped  ligaments  that anchor the spinal cord along its length to the dura mater on each side .  There are usually 21 denticulate ligaments on each side, with the uppermost pair occurring just below the  foramen magnum , and the lowest pair occurring between  spinal nerve roots  of T12 and L1. The denticulate ligaments are traditionally believed to provide stability for the spinal cord against motion within the  vertebral column . Their tooth-like appearance originates the word which derives from Latin  denticulatus , from  denticulus  (meaning ‘small tooth’).

9. The main difference between cranial and spinal meninges ; C ranial  meninges are the protective coverings of the brain, consisting of channels in the dura mater between various parts of the brain called  dural  folds, whereas spinal meninges are the protective coverings of the  spinal cord  whose dura mater acts as a  dural  sheath.  Cranial meninges contain two layers in the dura mater while the spinal meninges contain a single layer in the dura mater. In addition, cranial meninges may not produce an epidural space while spinal meninges produce an epidural space filled with fat .  

10. Clinical significance Injuries involving the meninges, can result in a  hemorrhage  and /or   hematoma . A  subarachnoid hemorrhage  is acute bleeding under the arachnoid; it may occur spontaneously or as a result of trauma . A  subdural hematoma  is a  hematoma  (collection of blood) located in a separation of the  arachnoid  from the  dura mater . The  bridging veins  that connect the  dura mater  and the  arachnoid  are torn, usually during an accident, and blood leaks into this area. An  epidural hematoma , bleeding between the dura mater and the  skull , may arise after an accident or spontaneously. Other medical conditions that affect the meninges include  meningitis  (usually from a  fungal ,  bacterial , or  viral   infection ) and  meningiomas  that arise from the meninges, or from  meningeal carcinomatoses  ( tumors ) that form elsewhere in the body and  metastasize  to the meninges.

11. Meningitis refers to  inflammation  of the meninges. It is usually caused by pathogens, but can be drug induced .   The immune response to the infection causes  cerebral oedema , consequently raising intra-cranial pressure. Part of the brain can be forced out of the cranial cavity – this is known as  cranial herniation . A cerebrospinal fluid (CSF) rhinorrhoea   occurs when there is a fistula between the dura and the skull base and discharge of CSF from the nose. CSF rhinorrhea or liquorrhoea commonly occurs following head trauma ( fronto -basal skull fractures), as a result of intracranial surgery, or destruction lesions.