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THE MENINGES - Central Nervous System ppt. Presentation
- 1. THE MENINGES BY DRNANNUNGI BRENDAH
- 2. Introduction • The brainin the skull is surrounded by three protective membranes, or meninges: a. The dura mater b. The arachnoid mater c. The pia mater. • The spinal cord in the vertebral column is also surrounded by three meninges.
- 3. Dura Mater ofthe Brain • The dura mater is conventionally described as two layers: a. The endosteal layer. b. The meningeal layer. • These are closely united except along certain lines, where they separate to form venous sinuses.
- 4. Dura matter- endosteallayer • The endosteal layer is nothing more than the ordinary periosteum covering the inner surface of the skull bones. It does not extend through the foramen magnum. • Around the margins of all the foramina in the skull, it becomes continuous with the periosteum on the outside of the skull bones. • At the sutures, it is continuous with the sutural ligaments. It is most strongly adherent to the bones over the base of the skull.
- 5. Dura matter- meningeallayer • The meningeal layer is the dura mater proper. • It is a dense, strong, fibrous membrane covering the brain and is continuous through the foramen magnum with the dura mater of the spinal cord. • It provides tubular sheaths for the cranial nerves as the latter pass through the foramina in the skull. • Outside the skull, the sheaths fuse with the epineurium of the nerves.
- 6. Dura matter- meningeallayer • The meningeal layer sends inward four septa that divide the cranial cavity into freely communicating spaces lodging the subdivisions of the brain. • The function of these septa is to restrict the rotatory displacement of the brain. • These include, a. Falx cerebri b. Falx cerebelli c. Tentorium cerebelli d. Diapragma sella
- 11. Falx cerebri • Thefalx cerebri is a sickle-shaped fold of dura mater that lies in the midline between the two cerebral hemispheres. • Its narrow end in front is attached to the internal frontal crest and the crista galli. • Its broad posterior part blends in the midline with the upper surface of the tentorium cerebelli. • The superior sagittal sinus runs in its upper fixed margin, the inferior sagittal sinus runs in its lower concave free margin, and the straight sinus runs along its attachment to the tentorium cerebelli.
- 13. Tentorium cerebrelli • Thetentorium cerebelli is a crescent-shaped fold of dura mater that roofs over the posterior cranial fossa • It covers the upper surface of the cerebellum and supports the occipital lobes of the cerebral hemispheres. • In front is a gap, the tentorial notch, for the passage of the midbrain and thus producing an inner free border and an outer attached or fixed border. • The fixed border is attached to the posterior clinoid processes, the superior borders of the petrous bones, and the margins of the grooves for the transverse sinuses on the occipital bone.
- 17. Tentorium cerebrelli • Thefree border runs forward at its two ends, crosses the attached border, and is affixed to the anterior clinoid process on each side. • At the point where the two borders cross, the third and fourth cranial nerves pass forward to enter the lateral wall of the cavernous sinus. • Close to the apex of the petrous part of the temporal bone, the lower layer of the tentorium is pouched forward beneath the superior petrosal sinus to form a recess for the trigeminal nerve and the trigeminal ganglion
- 18. Tentorium cerebrelli • Thefalx cerebri and the falx cerebelli are attached to the upper and lower surfaces of the tentorium, respectively. • The straight sinus runs along its attachment to the falx cerebri • The superior petrosal sinus along its attachment to the petrous bone • The transverse sinus along its attachment to the occipital bone
- 20. Falx cerebelli • Isa small, sickle-shaped fold of dura mater that is attached to the internal occipital crest. • Projects forward between the two cerebellar hemispheres. • Its posterior fixed margin contains the occipital sinus.
- 22. Diaphragma sellae • Thediaphragma sellae is a small circular fold of dura mater that forms the roof for the sella turcica. • A small opening in its center allows passage of the stalk of the pituitary gland
- 25. Dural Nerve Supply •Branches of the trigeminal, vagus, and first three cervical nerves and branches from the sympathetic system pass to the dura. • Numerous sensory endings are in the dura. The dura is sensitive to stretching, which produces the sensation of headache. • Stimulation of the sensory endings of the trigeminal nerve above the level of the tentorium cerebelli produces referred pain to an area of skin on the same side of the head. • Stimulation of the dural endings below the level of the tentorium produces referred pain to the back of the neck and back of the scalp along the distribution of the greater occipital nerve.
- 27. Dural Arterial Supply •Numerous arteries supply the dura mater from the internal carotid, maxillary, ascending pharyngeal, occipital, and vertebral arteries. • The most important is the middle meningeal artery, which is commonly damaged in head injuries.
- 28. Dural Arterial Supply •The middle meningeal artery arises from the maxillary artery in the infratemporal fossa. • It enters the cranial cavity and runs forward and laterally in a groove on the upper surface of the squamous part of the temporal bone. • To enter the cranial cavity, it passes through the foramen spinosum to lie between the meningeal and endosteal layers of dura.
- 29. Dural Arterial Supply •The anterior (frontal) branch deeply grooves or tunnels the anteroinferior angle of the parietal bone, and its course corresponds roughly to the line of the underlying precentral gyrus of the brain. • The posterior (parietal) branch curves backward and supplies the posterior part of the dura mater.
- 30. Dural Venous Drainage •The meningeal veins lie in the endosteal layer of dura. • The middle meningeal vein follows the branches of the middle meningeal artery and drains into the pterygoid venous plexus or the sphenoparietal sinus. • The veins lie lateral to the arteries.
- 31. Arachnoid Mater ofthe Brain • The arachnoid mater is a delicate, impermeable membrane covering the brain and lying between the pia mater internally and the dura mater externally. • It is separated from the dura by a potential space, the subdural space, and from the pia by the subarachnoid space, which is filled with cerebrospinal fluid. • The arachnoid bridges over the sulci on the surface of the brain, and in certain situations the arachnoid and pia are widely separated to form the subarachnoid cisternae.
- 33. Arachnoid Mater ofthe Brain • In certain areas, the arachnoid projects into the venous sinuses to form arachnoid villi. • The arachnoid villi are most numerous along the superior sagittal sinus. • Aggregations of arachnoid villi are referred to as arachnoid granulations. • Arachnoid villi serve as sites where the cerebrospinal fluid diffuses into the bloodstream. • It is important to remember that structures passing to and from the brain to the skull or its foramina must pass through the subarachnoid space.
- 34. Arachnoid Mater ofthe Brain • All the cerebral arteries and veins lie in the space, as do the cranial nerves • The arachnoid fuses with the epineurium of the nerves at their point of exit from the skull. • In the case of the optic nerve, the arachnoid forms a sheath for the nerve that extends into the orbital cavity through the optic canal and fuses with the sclera of the eyeball, thus, the subarachnoid space extends around the optic nerve as far as the eyeball
- 35. Arachnoid Mater ofthe Brain • The cerebrospinal fluid is produced by the choroid plexuses within the lateral, third, and fourth ventricles of the brain. • It escapes from the ventricular system of the brain through the three foramina in the roof of the fourth ventricle and so enters the subarachnoid space. • It now circulates both upward over the surfaces of the cerebral hemispheres and downward around the spinal cord. • The spinal subarachnoid space extends down as far as the second sacral vertebra
- 36. Arachnoid Mater ofthe Brain • Eventually, the fluid enters the bloodstream by passing into the arachnoid villi and diffusing through their walls. • In addition to removing waste products associated with neuronal activity, the cerebrospinal fluid provides a fluid medium in which the brain floats. This mechanism effectively protects the brain from trauma.
- 37. Pia Mater ofthe Brain • The pia mater is a vascular membrane that closely invests the brain, covering the gyri and descending into the deepest sulci. • It extends over the cranial nerves and fuses with their epineurium. • The cerebral arteries entering the substance of the brain carry a sheath of pia with them.
- 39. Clinical Correlates 1. Extraduralhemorrhage 2. Subdural hemorrhage 3. Cerebral hemorrhage 4. Subarachinoid hemorrhage 5. Intracranial hemorrhage of the infant
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- 41. Extradural hemorrhage • Alsocalled epidural hemorrhage • Results from injuries to the meningeal arteries or veins. • The most common artery to be damaged is the anterior division of the middle meningeal artery. • A comparatively minor blow to the side of the head, resulting in fracture of the skull in the region of the anteroinferior portion of the parietal bone, may sever the artery. • The arterial or venous injury is especially liable to occur if the artery and vein enter a bony canal in this region.
- 42. Extradural hemorrhage • Bleedingoccurs and strips up the meningeal layer of dura from the internal surface of the skull. • The intracranial pressure rises, and the enlarging blood clot exerts local pressure on the underlying motor area in the precentral gyrus. • Blood may also pass outward through the fracture line to form a soft swelling under the temporalis muscle. • To stop the hemorrhage, the torn artery or vein must be ligated or plugged. • The burr hole through the skull wall should be placed about 1 to 1.5 in. (2.5 to 4 cm) above the midpoint of the zygomatic arch.
- 43. Extradural hemorrhage • Abiconvex (lens-shaped) or crescent-shaped • Hyperdense (acute), isodense (subacute), hypodense (chronic) collection of blood located between the inner skull bone and the dura mater • Often seen in the temporal region • Typically does not cross suture lines.
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- 47. Subdural hemorrhage • Resultsfrom tearing of the superior cerebral veins at their point of entrance into the superior sagittal sinus. • The cause is usually a blow on the front or the back othe head, causing excessive anteroposterior displacement of the brain within the skull. • This condition, which is much more common than middle meningeal hemorrhage, can be produced by a sudden minor blow. • Once the vein is torn, blood under low pressure begins to accumulate in the potential space between the dura and the arachnoid. • In about half the cases, the condition is bilateral.
- 48. Subdural hemorrhage • Acuteand chronic forms of the clinical condition occur, depending on the speed of accumulation of fluid in the subdural space. • For example, if the patient starts to vomit, the venous pressure will rise as a result of a rise in the intrathoracic pressure. Under these circumstances, the subdural blood clot will increase rapidly in size and produce acute symptoms. • In the chronic form, over a course of several months, the small blood clot will attract fluid by osmosis so that a hemorrhagic cyst is formed, which gradually expands and produces pressure symptoms. • In both forms, the blood clot must be removed through burr holes in the skull.
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- 50. Subacute and ChronicSubdural hemorrhage
- 51. Subarachnoid hemorrhage • Resultsfrom leakage or rupture of a congenital aneurysm on the circle of Willis or, less commonly, from an angioma. • The symptoms, which are sudden in onset, • They include severe headache, stiffness of the neck, and loss of consciousness. • The diagnosis is established by withdrawing heavily blood-stained cerebrospinal fluid through a lumbar puncture
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- 53. Cerebral hemorrhage • Generallycaused by rupture of the thin-walled lenticulostriate artery, a branch of the middle cerebral artery. • The hemorrhage involves the vital corticobulbar and corticospinal fibers in the internal capsule and produces hemiplegia on the opposite side of the body. • The patient immediately loses consciousness, and the paralysis is evident when consciousness is regained.
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- 55. Intracranial Hemorrhage inthe Infant • Intracranial hemorrhage in the infant may occur during birth and may result from excessive molding of the head. • Bleeding may occur from the cerebral veins or the venous sinuses. • Excessive anteroposterior compression of the head often tears the anterior attachment of the falx cerebri from the tentorium cerebelli. • Bleeding then takes place from the great cerebral veins, the straight sinus, or the inferior sagittal sinus.