Meninges, Ventricular System, and CSF

• Topic: Meninges of the CNS, ventricular system, cerebrospinal fluid

Meninges/Capsule of the Central Nervous System

• Dura mater is a double-layered, fibrous outer membrane that originates from the mesoderm layer
• Arachnoid mater and Pia mater are two layers of the meninges collectively are known as Leptomeninges which originate from the neurectoderm layer

Cranial Meninges

• Dura Mater: The outermost and fibrous protective layer of the CNS
  • Endosteal Layer: Adheres to the cranial vault, does not go beyond the foreamen magnun
  • Meningeal Layer: Applied to the brains surface, and extends through the foramen magnum as "spinal dura"
• Arachnoid Mater has a cobweb-like structure
  • Arachnoid barrier cells barrier cells protecting the CNS
  • Arachnoid trabecular Layer: layer with loose fiber that helps keep the brain suspended
• Pia mater innermost and flimsy layer that dips into the sulci and fissures of thr brain and spinal cord
• Dural border cells are modified fibroblasts lining the inner surface of the meningeal dura.
  • in case of direct injury, they elicit a local inflammatory response in the region leading to angiogenesis and scar tissue formation.

Sensory Innervation of Dura Mater

• The dura mater of the floors of the middle and anterior cranial fossae and the posterior cranial fossae (tentorium cerebelli), is innervated by the meningeal branches of the CN V
  • Anterior meningeal branches of ethmoidal nerves (V1)
  • Meningeal branches of V2 and V3
  • Tentorial branch (from V1)
• The dura of the posterior cranial fossa floor is innervated by the C2 and C3 spinal nerves.

Clinical Correlate

• Headaches are dural in origin; pain is referred to the cutaneous/mucosal areas innervated by the corresponding trigeminal nerve division or cervical spinal nerve
• Intracranial pathology correlates include meningiomas, meningitis, and intracranial hemorrhage
• Extracranial pathology correlates include ophthalmic infections, sinusitis, shingles, dental infections, cervical disc pathology, syringomyelia, and muscular spasm (neck extensors)

Foldings of Meningeal Layer of Dura Mater

• Supra tentorial compartment includes cerebral hemispheres, pituitary gland, optic tracts, olfactory nerves
• Infra tentorial Compartment Includes: cerebellar hemispheres, brainstem, attached cranial nerves

Cranial dural spaces and their contents

• Epidural space is a potential space b/w cranial bone and periosteal dura.
  • Contains arteries supplying the dura mater
  • Cranial & spinal epidural spaces do not communicate with each other
  • The main contents are the meningeal arteries, which supply blood to the dura mater
• Subdural space: the area between the meningeal dura and arachnoid mater
  • Is is continuous down as the spinal subdural space
  • Contains small vertically running bridging veins that connect the cerebral veins with the dural venous sinuses

Differences B/W Cranial & Vertebral Epidural Spaces

• Intracranial Epidural Space: the potential space b/w the endosteal layer of the dura mater and the cranial bones
  • it is occupied by meningeal arteries supplying the dura mater
  • It only becomes visible in abnormal blood accumulation b/w the bone and endosteal dura
• Spinal Epidural Space: actial physical space between the bony vertebral canal and the spinal dura mater
  • Commonly used for multiple invasive procedures (epidural anesthesia, chemotherapy drug administration, etc.)

Epidural and Subdural Hematomas

• Epidural bleed: almost always an arterial bleed (middle meningeal artery) grows fast followed by blunt head trauma, assumes the contour of the bone
• Subdural Hematoma: Appears like a Cresent on the CAT scan, and grows at a slow pace which is a venous bleed, tearing/laceration of bridging veins, generally due to atrophy of brain tissue that occurs in ederly alcoholics

Dural Venous Sinuses

• Venous channels are located between the periosteal and meningeal layers of the dura.
• They drain the entire intracranial venous blood and the CSF into the right ventricle via the internal jugular veins
• The dural venous sinues are valveless channels, hence allow a forward or backflow of blood between the intra and extra cranial structures
• Structures draining into the dural sinuses
• Emissary veins: progress through the skull and allow communication between intracranial and extracranial contents
• Diplopic veins: drain blood between the inner and outer layer of flat bones of the skull (diploe)
• Meningeal veins
• Arachnoid granulations: returning CSF to the venous circulation
• Cerebral and cerebellar veins: cross the subdural space to drain into the superior sagittal vein, hence, the name “bridging veins”

Cerebral Venous Sinus Thrombosis (CVST)

• CVST is a medical emergency
• Causes include: Coagulopathies, Hypercoagulable states, Head injuries, Infections, etc.
• Cavernous Sinus Thrombosis is a rare but potential complication which can follow a facial or orbital infection.
• Causes severe headache, symptoms of raised ICP.
• Due to an extracranial connection of the cavernous sinus with the angular vein via the ophthalmic veins thrombophlebitis of the facial vein may extend to the cavernous sinus

Arachnoid Mater

• A thin avascular membrane bridges over the sulci of the brain, mainly consisting of elastic fibers
• Has a smooth outer surface composed of flat cells connected by tight junctions, forming a barrier
• The inner layer is rough and is covered in loosely arranged spiderweb like cells that span and attach to PIa Mater, help keep the brain in place
• Arachnoid tissue thickness varies in sections of the brain. thin over convolutions but thickens over brain stem
• It becomes opaque and widley seperated from underlying Pia Matter in the brainstem region

Regional Specialization of Arachnoid Mater

• Arachnoid villi - finger-like projections that go into the dural venous sinuses.
  • The core composes of interconnecting tubules that act like one-way valves.
• Arachnoid Granulations are aggregates/tufts of villi in the superior sagittal sinus
• Arachnoid Cap Cells is a cluster of cells that help cover arachnoid villi tips
  • They connect directly to venous sinus blood and epithelial cells & blend with the endothelial lining of the venous sinus. -Most of the benign mengingeal tumors originate from the Archinoid Cap Cells

Functional significance of Arachnoid villi/granulations

• Removes extra CSF and releases it into dural sinuses, and helps maintain the amount of fluid in the subarachnoid space
• CSf lows into the dural sinuses by arachnoid vili under a pressure gradient
• Fluid proceeds via active support through bulk transport cells
• malfunctioning achinoid vili cuases acumination of excess CSF in the sub arachnoid space resulting in hydrocephalus

Subarachnoid Space & Arachnoid Cisterns

• A area in between the arachnoid mater and pia mater filled with CSF, and wraps around the countours of the brain and goes down to the spinal cord
• Contents: Blood Vessles and Cranial Nerves are located in this space Expansions of space at the base of brain with CSF fillied, which surrounds the brainstem Major Subarachnoid Cisterns & their contents can be :
• Interpeduncular cistern: ventral to midbrain, contains CN III and Mammillary bodies
• Chiasmatic/Suprasellar cistern: below/ventral to hypothalamus, contains optic chiasm & pituitary stalk
• Ambient cistern: dorsal to midbrain above cerebellum, encircles midbrain, includes: Pineal gland, CN IV, Great cerebral vein, Posterior cerebral artery
• Pontine cistern: lies anterior to pons, includes basilar artery, anterior inferior cerebellar arteries, CN VI, & superior cerebellar arteries communicates with the Interpeduncular cistern.
• Cisterna magna: cerebellum contains cerebellar arteries, CN IX, X, XI.
• Lumbar cistern: present at base of spinal cord, extends from L2 to the second sacral vertebra, contains cauda equina that is used for clinical proceudes such as lumbar punture or intra-thecal injections

Subarachnoid Hemorrhage and Effacement of Subarachnoid cisterns

• Rupturing a cerebral artery can cause Hemorrhage, filling the mesecephalic subarachnoid with blood and cisterns
• Effacement: When the artery cistern appear indistinct on the MRI mostly by Diffuse cerebral edema and brain tumors

Pia Mater

• The Pia Mater is the only membrane that adheres to the brain surface and projects into the sulci and composed of flat mesothelial cells
• Virchow-Robin Spaces contain CSF that surround the Brain, the contain macrophages and is thougth to drain interstital fluid In enlarged situations this can cases things like CEREBROVASCULAR Disease Clinical Correlates

Clinical Correlates

• Meningitis is Inflammation of eptomeninges by Bacteral and fungal reactions
• Complications of Meningitis is bacteria is exxudate formation
• Post Meningitis lead to fibrosis an hydrocephalus

Benign Tumors of Mengines

• Most common primary tumors in the bain (30%)
• Grows very Slowly over years
• Convexity meningioma: grows in brain from skull may not have symptoms to later parts
• Sphenoid wing meningioma: behind eyes on skill base 20% of tumors
• Olfactory groove meningioma - runs between brain and the nose, can lose sense of smell and 10% of tumors
• posterior Fossa Menginoima Underside if Brain 10% of tumors, trigeminal neuralgia

Ventricular System of the Brain and Spinal Cord

• Cavities of CNS derived from the cavity of the primitive neural tube.
• Courses through the brain as a pair of lateral ventricles, a single third ventricle, a tube-like cerebral aqueduct, rhomboid-shaped fourth ventricle, and a narrow central canal that travels down the spinal cord.
• the openings communicate with the subarachnoid space through openings called foramina

Lateral Ventricles

• Located in cerebrum, the cavity divides into: -Frontal/ Anterior Hom: It can be located in the frontal lobe and is located anterior to the froamen of Monro. The sides are bounded by the Septum Pelucidum -Medially, bounded by the septum pellucidum, fornix, and genu of corpus callosum.
  • The floor is formed by the rostrum of corpus callosum. -Temporal/Inferior Horn: Iocated in temporal lobe and bounded by the head of caudate Nucleus -Laterally: Head of Nucleaus in bulges It has:
  • Floor created by rostratum

Body of Lateral Ventricle

• Contral part of the Ventricle is located in of cerebrum and connects from Monroe to collosum

Atrium/Triagnle of Ventricle

• The eaisent to expand section, a portion of colosseum with the "chroid enlargement'

Third Ventricle

• Is located in the diencephalon, and communicates with the foremen of moro and ceberal aqueduct
• Important relationships
  • Vetrally- anterior
  • Dorsally- posterior comprimise
  • Laterrly - (right and Left) - Inferiorlly - OPtic chiasm
  • superior - fornnix

Cerebral Aqueduct of Sylvius

• Connects the midbrain and is is1.5-18 Cm long to the tentum/tegumentum of brains

Fourth Ventricle

• A single midline cavity is present in the hindbrain a diamond shape located between the Pons and Medulla
• Located above tent connects to the subarachnoid and cisterna.

Cerebrospinal Fluid Circulation

• Normal Flow of Fluid is about 500 mL Flow with ventricular system, enters through the foramina of Luschka
• Volume wise about 90-170 ml
  • ~23ml is in the ventricles
  • Rest is in the subarachnoid space where the ventricles flow in in it

Accumulation of CSF : HYROCEPHALOUS

• Accumulation of CSF in the brain that has outside of ventricles and inside the ventricle (Communication type)
• Flow outside Ventricular System
• Hemmorege
• Meningies

(Non comuncating Type) Flow inside Ventialtory system inside

• Stenosis in aquadurt
• Tumor in ventricular

Comuncating- Blocked outside but can go between ventriclar Non -Comiucating can be prenatal / post Natal from any trauma

Explore the protective meninges of the central nervous system, including the dura mater, arachnoid mater, and pia mater. Understand the structure and function of the ventricular system and the role of cerebrospinal fluid (CSF) in cushioning and nourishing the brain and spinal cord. Learn about the unique features of each meningeal layer and their collective importance in CNS protection.