BMS2-21 Dural Partitions Meninges CSF Venous Sinuses PDF

Dural Partitions Ventricular System Dural Venous Sinues Dr A. Aktar The Dural Partitions Meninges • The membranous coverings of the brain and spinal cord • 3 layers of meninges: • dura mater • arachnoid mater • pia mater • 2 major functions: • Provide a supportive framework for cerebral & cran...

Dural Partitions Ventricular System Dural Venous Sinues Dr A. Aktar The Dural Partitions Meninges • The membranous coverings of the brain and spinal cord • 3 layers of meninges: • dura mater • arachnoid mater • pia mater • 2 major functions: • Provide a supportive framework for cerebral & cranial vasculature • Protect CNS from mechanical damage (together w/CSF) • Meninges often involved cerebral pathology, as a common site of infection (meningitis) & intracranial bleeds Meninges Dura Mater • Outermost layer • Lies directly underneath bones of skull & vertebral column • Thick, tough, inextensible Meninges Dura Mater • 2 layers • Endosteal layer – Lines inner surface of bones of cranium • Meningeal layer – Lines the endosteal layer inside the cranial cavity. It is the only layer present in the vertebral column • Between these 2 layers: Dural venous sinuses • Responsible for venous vasculature of the cranium • Drain into internal jugular veins Meninges Dural Reflections • Partition the brain • Divide cranial cavity into several compartments Tentorium cerebelli : • divides cranial cavity into supratentorial & infratentorial compartments • Separates occipital lobe from cerebellum Small partition arises from under surface of the tentorium: Falx cerebelli • partially separates the two cerebellar hemispheres Meninges Tentorium Cerebelli : • divides cranial cavity into supratentorial & infratentorial compartments • Separates occipital lobe from cerebellum • small partition arises from under surface of the tentorium: Meninges Dural Reflections Falx Cerebri • A.k.a. median dural septum • Central partition • Attached to base of skull • L & R compartments • Prevents shift of cerebrum • Anteriorly attached to crista galli of ethmoid bone Meninges Dural Partitions Meninges Dural Partitions - Superior View• Tentorium cerebelli covers the posterior cranial fossa • Tentorium rises toward the midline where it forms the falx cerebri, (sectioned in this image to remove the cerebrum) • Frontal lobes lie in ant. cranial fossa • Temporal lobes lie in middle cranial fossa • Occipital lobes are positioned on the tentorium • Note L image R tentorium removed to reveal underlying posterior cranial fossa containing cerebellum & brainstem Meninges Dural Reflections Sellar Diaphragm (a.k.a. Diaphragma sellae) • Flat sheet of dura suspended btwn clinoid processes of sphenoid bone • Forms partial roof over hypophysial fossa • Covers pituitary gland • Has aperture for passage of infundibulum (pituitary stalk) and hypophysial veins • Post. boundary at dorsum sellae & ant. boundary at tuberculum sellae Meninges Dural Mater Vasculature & Innervation • Middle meningeal artery and vein • Runs under temporal bone • Trigeminal nerve (V1, V2 and V3)  Dura very sensitive Meninges Arachnoid Mater • Middle layer of meninges • Underneath dura mater • Consists of layers of connective tissue • Avascular • No innervation • Ends at S2 level • Btwn dura mater & arachnoid mater: Subdural space • Underneath arachnoid : Sub-arachnoid space • Contains cerebrospinal fluid Meninges Arachnoid Granulations • Small projections of arachnoid mater into dura • Allow CSF to re-enter the circulation via the dural venous sinuses. Meninges Pia Mater • Located underneath subarachnoid space • Very thin, & tightly adhered to surface of brain & spinal cord • The only covering to follow the contours of brain (gyri & fissures) • Highly vascularized • Blood vessels perforate through it to supply underlying neural tissue Layers External to internal : shown from R to L: Scalp Periosteum Bone Dura Mater Arachnoid Mater Pia Mater Brain Tissue Dura Mater 13 Figure 12.24 Meninges Clinical Correlate: Meningitis • Inflammation of the meninges. Usually caused by pathogens (bacteria or viruses) • Causes cerebral edema  rise in intracranial pressure • Part of brain can be forced out of cranial cavity –> cranial herniation • In combination with systemic hypotension, raised intracranial pressure reduces cerebral perfusion. The Ventricular System & CSF Cerebrospinal Fluid • CSF bathes brain & spinal cord – a protective “bath” • Hydromechanical protection of the CNS • Regulation of brain interstitial fluid homeostasis, which influences neuronal functioning • CSF space is a dynamic pressure system  CSF pressure determines intracranial pressure • CSF produced by lining of the ventricles, the choroid plexus • CSF circulation begins in the ventricles  then enters the subarachnoid space to surround brain & spinal cord Cerebrospinal Fluid Production & Barriers Choroid plexus : • Secretes CSF • Contains choroid epithelial cells • Present in all parts of ventricular system - lateral ventricles, 3rd & 4th ventricles - except cerebral aqueduct, frontal horn & occipital horn of lateral ventricles • CSF circulation begins in the ventricles  then enters subarachnoid space to surround brain & spinal cord • A total of 400 – 600 cc of CSF produced/day • Ventricles & subarachnoid space contain 50-150 cc  All of CSF is turned over 2 – 4 times per day Cerebrospinal Fluid Production & Barriers • Arachnoid granulations : Site of CSF resorption • Endothelium-lined finger-like meningeal protrusions into dural venous sinuses through dura mater • When cerebrospinal fluid pressure increases, arachnoid villi further develop, thereby increasing their surface of exchange & cerebrospinal fluid absorption (b) The Ventricles Ventricular system: a set of communicating cavities within brain 4 ventricles • Interconnected • Each part of brain contains a ventricle • R & L lateral ventricles, 3rd ventricle, 4th ventricle The Ventricles Lateral ventricles • Deep within each cerebral hemisphere • Central ‘body’ part • Ant (frontal) horn • Inf (temporal) horn • Post (occiptial) horn The Ventricles Lateral Ventricles Cornu ant Ant horn Collateral trigone Pars(central centralis Body part) Inf.Cornu horn inf • • • Pars centralis Trigonum collaterale Cornu inf’da plexus choroideus var. Inf. horn has choroid plexus Post. hornpost Cornu The Ventricles Collateral Trigone Also known as: Atrium of lateral ventricle • Surface feature of the lateral ventricle • Flattened triangular area located at junction of temporal horn & occipital horn of lateral ventricle The Ventricles Lateral Ventricles • Each communicates w/3rd ventricle via an interventricular foramen : Foramen of Munro The Ventricles Lateral Ventricles • In between the R & L lateral ventricle: septum pellucidum The Ventricles 3rd Ventricle • In midline within diencephalon – btwn thalamus & hypothalamus • Inthertahlamic adhesion is within 3rd ventricle • Upper wall contains choriod plexus • Communicates w/ 4th ventricle via cerebral aqueduct (of Sylvius) - which passes thru midbrain The Ventricles 4th Ventricle • Btwn dorsal surfaces of pons, upper medulla & ventral surface of cerebellum • Continuous w/central canal of lower medulla & spinal cord • 4 openings: • Median foramen of Magendie • 2 lateral foramen of Luschka • The lateral & medial openings connect to subarachnoid space! 4th Ventricle has choroid plexus on its inf. wall The Ventricles Saggital Hemisection Circulation of CSF Lateral ventricles  Foramen of Monroe  3rd Ventricle  Cerebral aqueduct (of Sylvius) 4th Ventricle  Foramen of Luschka & Median foramen of Magendie  Central spinal canal & subarachnoid space  Arachnoid granulations  dural venous sinuses • Arachnoid granulations (small projections of arachnoid mater) resorb & drain CSF into the dural venous sinuses Subarachnoid Cisterns • Wider areas of subarachnoid space, containing CSF • Cerebellomedulllary cistern – aka. Cisterna magna: Largest of the cisterns • Interpeduncular cistern: Contains the optic chiasm, circulus arteriosus cerebri*, oculomotor n. • Chiasmatic cistern • Ambient cistern : v. magna cerebri, a. cerebri posterior, a. cerebellaris superior, corpus pineale • Pontine cistern: Contains basilar a. • Cerebellopontine angle cistern: Contains CN VII & VIII, AICA • Lumbar cistern : Contains filum terminale, cauda equina Ventricular System 3-D Start video at 3.04 https://www.youtube.com/watch?v=zqQ6iKw5DjY The Ventricles & CSF Clinical Correlates • Hydrocephalus : an abnormal collection of CSF within the ventricles of the brain • Produces ventricular dilatation • • • • Communicating: Non communicating Normal pressure Ex vacuo Impaired CSF resorption or too much production or obstruction in subacarchnoid space Obstruction of flow at narrow points Impaired CSF resorption. Ventricles chronically dilated Excess CSF in regions where brain tissue lost to atrophy (stroke, surgery, trauma) • Protein concentration is CSF much lower vs in serum • Na, Cl & Mg concentrations higher and K & Ca concentrations lower than plasma • Chronobiological cycles of Na content : Peak Na conc at 8:00 am & at 6:00 pm • RBC not normally found in CSF Blood- CSF Barrier & Blood-Brain Barrier • Chemical integrity of brain protected in 2 ways Blood-Brain Barrier • Formed by capillary endothelium connected by tight junctions • Astrocytes foot processes contribute • Barrier not formed completely in neonates and premature births.  toxins such as biluribun can cause CNS symptoms Blood-CSF barrier • “Tight junctions” along epithelial cells of choroid plexus • The ability of a substance to gain access to the CSF does not guarantee it will access the brain Blood- CSF Barrier & Blood-Brain Barrier Clinical Correlate • Blood brain barrier not completely formed in neonates and premature births.  toxins such as biluribun can cause CNS symptoms • Some drugs used systemically can not access the CNS • E.g. Some antibiotics, anti-Parkinson drugs  Need to be chemically modified or administered into the subarachnoid space Structures Without Blood-Brain Barrier • Pineal gland • Neuro-hypophysis • Area postrema: Sensitive to emetic chemicals in bood - chemoreceptor function Regulates vomiting, thirst, hunger, blood pressure control Located on caudal part of floor of 4th ventricle Bilateral to mid-line Dural (Venous) Sinuses Dural (Venous) Sinuses • Collecting pools of blood • Btwn lamina interna & externa of dura mater • Cerebrum, cerebellum, brainstem drained by numerous veins empty into the dural venous sinuses • All ultimately drain into the internal jugular v. • Walls composed of dura mater lined with endothelium • Do not have valves • Lack a full set of vessel layers (e.g. tunica media) characteristic of arteries and veins • No muscle • Do not follow arterial supply • They also receive CSF from subarchnoid space via the arachnoid granulations Dural (Venous) Sinuses • Also receive CSF from subarchnoid space via the arachnoid granulations • Superficial veins of scalp & diploic veins (of cranial bone diploe) drain into them via emissary veins Dural Venous Sinuses Superior Sagittal Sinus • Starts behind foramen caecum (frontal bone) • Runs along sup. margin of falx cerebri • Drains from lateral aspects of ant. cerebral hemispheres to confluence of sinuses – at level of int. occiptital protuberance • Drains into ransverse sinuses Dural Venous Sinuses Venous Lacuna • 2 – 3 venous structures that drain from each side into the superior saggital sinus Dural Venous Sinuses Inferior Sagittal Sinus • In inferior margin of falx cerebri • Joins (terminates by) great cerebral vein of Galen to form the straight sinus at falx cerebri / tentorium cerebelli junction  drains into confluence of sinuses Dural Venous Sinuses Cavernous Sinus • Plexus of veins on either side of sella turcica • Surrounds int. carotid a. & cranial nerves III, IV, V1, V2, VI (oculomotor, trochlear, trigeminal, abducens) • Drains into (1) transverse sinus via sup.petrosal sinus & (2) internal jugular v. via inf. petrosal sinus Dural Venous Sinuses Superior Petrosal Sinus • Drains cavernous sinus • Passes backward & laterally : Drains into transverse sinus • Runs in margin of tentorium cerebelli, in a groove in petrous part of temporal bone formed by the sinus - the superior petrosal sulcus Dural Venous Sinuses Inferior Petrosal Sinus • Small paired situated on inferior border of petrous part of temporal bone on each side • Drains the cavernous sinus into the internal jugular vein • Passes thru anterior compartment of jugular foramen Dural Venous Sinuses Straight Sinus • At junction of falx cerberi & tentorium cerebelli • Usually drains into L transverse sinus Transverse Sinus & Straight Sinus Sinus sigmoideus ile devam edr. Transverse Sinus Transverse sinus Dural Venous Sinuses Dural Venous Sinuses Sigmoid Sinus • Sigma shaped : Σ • Receives blood from transverse sinus • Converges with the inferior petrosal sinuses to form the internal jugular vein