Neuro H&N

Cranial Meninges

• Connective tissue surrounds the central nervous system, including the brain and spinal cord
• Derived from the mesoderm (dura mater) and the neural crest (arachnoid and pia mater) between 20-35 days of development
• Consists of three layers: dura mater, arachnoid mater, and pia mater

Dura Mater

• Also known as the pachymeninx, it is the outer layer
• A hard, fibrous bilaminar membrane composed of fibroblasts and collagen fibrils
• Adheres to the inner surface of the skull and vertebrae

Dura Mater Layers

• Periosteal dura layer:
  • Contains larger and less elongated fibroblasts
  • Highly vascular and innervated
• Meningeal dura layer:
  • Contains flattened and elongated fibroblasts
  • Smaller nuclei and darker cytoplasm
  • Smooth, avascular, and lined by mesothelium
  • Continuous with spinal dura mater
  • Infoldings and septa are produced within this layer

Dura Mater Border Cell Portions

• Contains flattened fibroblasts with sinuous processes and is a source of weakness at the dura-arachnoid junction because:
  • Fibroblasts have a loose arrangement
  • There is no collagen/elastic fibres
  • Extracellular spaces have enlarged

Dura Infoldings/Reflections

• The mostly fused two layers sometimes separate to form venous sinuses and create dural reflections
• Dural reflections refer to spots where two meningeal layers enter the cranial cavity, forming septa that divide the brain
• Includes:
  • Falx cerebri
  • Tentorium cerebelli
  • Falx cerebelli
  • Diaphragma sellae
• Falx cerebri and tentorium cerebelli are the two main dural reflections

Falx Cerebri

• The largest of the dural reflections
• It attaches from the frontal crest and crista galli (anteriorly) and to the internal occipital protuberance (posteriorly)
• Suspends down into the interhemispheric fissure, which separates the right and left cerebral hemispheres
• Continuous with the tentorium cerebelli

Tentorium Cerebelli

• The second largest dural reflection
• It attaches rostrally to the clinoid processes (sphenoid), rostrolaterally to the petrous part (temporal bone), and posterolaterally to the internal surface of the occipital & parietal bones
• Divides the occipital lobe from the cerebellum
• Tentorial notch is an opening in the falx cerebri that allows the midbrain to pass into the middle cranial fossa

Falx Cerebelli

• Inferior to the cerebellar tentorium
• Partially separates the cerebellar hemispheres

Diaphragma Sellae

• A small circular fold that covers the hypophyseal fossa
• Forms the roof of the sella turcica, and houses the pituitary gland
• The infundibular stalk passes through a small hole in the center

Dura Mater Vascularity

• Highly vascularized via the meningeal arteries
• Anterior cranial fossa: anterior meningeal artery (from ethmoidal aa)
• Middle cranial fossa: middle meningeal artery (MMA), accessory meningeal (both from maxillary aa)
• Posterior cranial fossa: meningeal branches from ascending pharyngeal and occipital aa, branches from vertebral arteries

Dura Mater Nerve Supply

• Innervated by the tentorial nerve, a branch of the ophthalmic division of the trigeminal nerve, particularly the tentorium cerebelli and the posterior third of the falx cerebri
• Cranial Fossa Innervation:
  • Anterior: Anterior and posterior ethmoidal nerve (CN V1)
  • Middle: Maxillary (CN V2)
  • Posterior (infratentorial dura): C2 and C3 (C1 when present) - or via meningeal branches of the Vagus nerve (CN X)

Arachnoid Mater

• Referred to as the leptomeninx, the inner layer
• A delicate, avascular layer located internal to the dural border cells
• Tightly attached to the inner layer of the dura mater
• Divided into 2 layers: arachnoid barrier cell layer and arachnoid trabeculae

Arachnoid Barrier Cell Layer

• Contains tight junctions that function as a barrier against fluid movement and provide strength to the membrane
• The layer has no collagen

Arachnoid Trabeculae

• Composed of spindle cells (fibroblasts) that traverse the subarachnoid space, helping to keep the brain suspended

Subarachnoid Space

• Fluid filled cavity, the subarachnoid (leptomeningeal) space is vital for the brains normal function
• The contents: CSF, trabecular cells, collagen fibrils, arteries, veins, and the roots of cranial nerves
• Rupture of vessels by trauma/spontaneously: subarachnoid hemorrhage

Pia Mater

• The innermost layer of the meninges
• Tightly attached to the brain and spinal cord
• Thicker in the spinal cord
• Projects into fissures and sulci
• Consists of a small plexus of blood vessels in connective tissue, covered externally with mesothelial cells nourishing the brain
• Separated from the brain by a glial basement membrane and the subpial space
• Perivascular space (Virchow-Robin's space): space created by penetrating vessels that may serve as a channel for CNS movement to the brain tissue

Differences Between Cranial and Spinal Epidural Spaces

• Cranial dura mater: attached to the inner skull surface, consists of two fused layers: periosteal and meningeal
• Spinal dura mater: separated from vertebrae by the epidural space, consists of only the meningeal dura
• Dura mater stops at the foramen magnum
• Spinal cord is covered by the meningeal layer which continues in the vertebral canal
• Attaches caudally by the filum terminale externum or coccygeal ligament

The Meninges and the Spinal Cord

• The meninges also cover the spinal cord
• The spinal cord is anchored in the subarachnoid space by denticulate ligaments, filum terminale internum, and filum terminale externum
• Only one layer of dura mater in the spinal cord
• True spinal epidural space is filled with fatty tissue and the vertebral venous plexus
• Conus medullaris is the caudal end of the spinal cord

Meningeal Spaces in the Brain

• Extradural or epidural: potential space outside the dura, containing meningeal arteries
• Subdural: lies between the arachnoid and dura, crossed by bridging veins
• Subarachnoid: lies between the pia and arachnoid, terminating at the S2 vertebra

Epidural (Extradural) Hematoma

• Blood accumulation in the potential space between the skull and dura
• Skull fracture (~85%) due to the middle meningeal artery
• Epidural hematomas do not cross suture lines
• Lesions are frequently large, lens-shaped, may appear loculated, short, and thick
  • Symptoms: headaches, seizures, vomiting, hyperactive reflexes, coma; untreated: death
• Treatment: surgical removal of the clot and coagulation of the damaged vessel

Subdural Hematoma

• More common than epidural hematoma
• Dural border hemorrhage typically follows a hard blow to the head causing brain movement and injury inside the cranium
• Linked to intracranial bleeds/contusions, mental status decline over days
• Observed with "Shaken Baby Syndrome," in alcoholics, car accidents
• Venous bleeding from rupture of bridging veins (from brain to the arachnoid and dura) slowly accumulates in the subdural space between the dura and arachnoid
• Develop due to minor trauma
• Imaging shows crescent-shaped enhancement that crosses suture lines but doesn’t cross the midline

Subarachnoid Hemorrhage

• Caused by aneurysm ruptures, leading to "the worst headache of my life"
• Medical emergency
• Typically follows ruptured cerebral aneurysm (~75-80%) or arteriovenous malformation (AVM) into the subarachnoid space
  • May result in meningeal irritation, severe headache, stiff neck, and often loss of consciousness
• Imaging shows enhancement in the area of the hemorrhage
• Risk factors: hypertension, smoking, connective tissue disorders, autosomal dominant polycystic kidney disease (ADPKD), older age

Epidural vs Subdural Hematoma

• Subdural hematomas present in three forms: acute (detected soon after trauma), subacute (symptoms develop in days/weeks after injury), or chronic (symptoms occur weeks/months after injury
• Hematomas diagnosed with CT/MRI; if suspected, neurosurgical evaluation is urgently performed

Meningitis

• Meningitis: inflammation of the meninges
  • bacterial: high fever, headache, nuchal rigidity, Kernig and Brudzinski signs
  • fungal: immunocompromised patients (Cryptococcus), organism highly dependent on geography
  • viral (aseptic): like bacterial but less acute, onset less severe -Bacterial: Inflammation of the meninges because of bacteria invading the subarachnoid space, most commonly Streptococcus pneumoniae, Neisseria meningitides, and Escherichia coli -Bacteria can access the person's meninges via the bloodstream or ear and sinus infections, a defect in the dura mater, or via surgical neurological procedures - Infants, 2 years and under, and people with a weakened immune system are at higher risk - Can be treated with antibiotic therapy and vaccinations
• Lumbar Puncture: collect CSF and find presence of neutrophils/lymphocytes

Meningioma

• Meningiomas: primary tumors of the meninges in the brain and spinal cord, 95% are benign -Benign tumors of the brain are slow growing and don't cause problems until they compress nervous structures. -Malignant tumors of the brain are fast growing that often cause neurological problems and swelling of the brain -Surgical removal or radiation therapy is the choice of treatment

Brain Ventricular System

• The ventricles are cavities in each hemisphere that contain CSF.
• CSF derived from the cavity of the neural tube is an important source of electrolytes, protects/supports the brain, and is a conduit for neuroactive+ metabolic products.
• There are 2 lateral ventricles, 1 third ventricle, and 1 fourth ventricle
• The aqueduct is the most common site of stenosis.
• The 4th ventricle communicates with the subarachnoid space through two lateral foramina of Luschka and one foramen of Magendie.

Ventricles and Related Structures

• Includes the Corpus Callosum and Caduate Nucleus
• Anterior Horn, Head of caudate, atrium are the anterior ventricle
• Third ventricle, Amygdala, tail of caudate and Inferior horn are the posterior
• Related Structures: Thalamus and Amygdaloid Complex

Third Ventricle

• Narrow, vertical oriented diencephalon cavity that communicates with the lateral ventricles (rostrally) and cerebral aqueduct (caudally)
• Floor formed by opic chiasm, the infindibulum, and recesses
• Related structures: hypothalamus, thalamus, supraoptic recess, infundibular recess, suprapineal recess, anterior commissure, and Lamina terminals

Fourth Ventricle

• A Tent-shaped cavity or pyramid-shaped space that projects to the cerebellum an caudal tapers to a narrow channel

Cerebral Aqueduct

• The Ventricle extends through the mesencephalon ~1.5 mm in diameter -This ventricle has no choroid plexus.
• Is susceptible to vascular occlusion and is surrounded by the periaqueductal gray (PAG)

Ventricular System's Ependyma

• Ventricular system by a single layer of epithelial cells, the cerebral ependyma
• A portion of 30%, of the cerebral spinal fluid is secreted by the parenchima of the brain which crosses ependyma while the 70% is made by the chorid plexus

Choroid Plexus

• Located in each ventricle
• Produces about 70% of CSF
• Enzyme carbonic anhydrase helps produce CSF
• A secretory epitelial tissue is made up of, -Choriod plexus epithelial cell -Tight junctions -Blood Choriod plexus
  • Stromal cells which are fenestrated endothelial cells

CSF Circulation

• CSF Flows through these locations
  • Choriod plexus
  • Lateral Ventricle
  • Thalamaus
  • Thalamucortical
  • Fastigium
  • Choroid Plexus

Cerebrospinal Fluid Function

• Buoyant effect, prevent from crushing
• Cushioing Effect
• Removes the Metabolites
• Constant stable ionic environment
• The average valume Adult CSF = 120 - 140 mL daily
• The production rate is 15 - 20 mL or 400 -500 mL's daily
• The brain weights, normally air is reduced to ~40'gs while in CSF

Aneurysm

• Dilation of a vessel wall, typically at branch points or sharp turns in vessels
• Can be of different forms:
  • Berry or saccular
  • Giant (diameter > 2 cm)
  • Fusiform
• Occurs most commonly in the internal carotid system
  • 85% of aneurysms develop at branches of the internal carotid system
  • 10-15% in the vertebrobasilar system
• Most common site is the anterior communicating artery, and give rise to bitemporal hemianopia
• Rupture of cerebral aneurysms can result hemorrhage and stroke and lead to neurological death

Cerebral Embolism

• Can result in subsequent cerebral ischemia, infarction, and necrosis
• Cerebral Embolisms are caused by occlusions of a vessel by:
  • Clot
  • Tumor cells
  • Bacterial Clump
  • Air
  • Plaque Fragments
• A thrombus is an embolus derived from blood
• The carotid bifurcation is a frequent location for atherosclerotic narrowing, potentially leading to ischemia and stroke.

Penumbra

• Occurs during an occlusive or ischemic stroke
• Three areas of concern: · Central portion: dead tissue · Immediately surrounding area: penumbra · Area outside the Penumbra

Arteriovenous Malformation (AVM)

• Abnormal communication between arteries and veins due to failure of the capillary bed to develop normally
• Leads to large arteries connecting with large veins and little to no normal brain tissue in the area
• AVMs are dynamic and typically identified in the second or third decade of life
• Signs and Symptoms: Hemorrhage, seizures, mass effect, increased intracranial pressure, hydrocephalus

Arterial Blood Supply

• Internal Carotid Artery
  • Supplies oxygen-rich blood
  • Originates from the common carotid artery
  • Enters the cranial cavity through the carotid canal
• Vertebral Artery:
  • Originates from the subclavian artery
  • Enters the cranial cavity through the foramen magnum
• On the right side, the common carotid artery originates from the brachiocephalic trunk
• On the left side, it originates from the arch of the aorta

Internal Carotid Artery (ICA) Parts

• Cervical: ascends vertically in the neck
• Petrous: turns horizontally and medially in the carotid canal
• Cavernous: traverses the cavernous sinus and makes a 180° turn inferior to the anterior clinoid process
• Cerebral: within the cranial cavity
• The foramen lacerum is closed in life by cartilage

Cerebral Circulatory System Arteries

• Anterior Cerebral Artery / Anterior Choroidal Artery
• Middle Cerebral Artery
• Anterior Communicating Artery
• Internal Carotid Artery
• Posterior Communicating Artery
• Basilar Artery
• Superior Cerebellar Artery
• Labyrinthine Artery
• Anterior Inferior Cerebellar Artery
• Posterior Inferior Cerebellar Artery
• Vertebral Artery
• Meningeal Artery / Anterior and Posterior Spinal Medullary Artery

Internal Carotid Artery Branches

• Ophthalmic artery
  • Occlusion leads to sudden-onset blindness from the central artery retina
• Posterior communicating artery -Supplies hypophysis, infundibulum, hypothalamus, thalamus, and hippocampus
• Anterior communicating artery -Most common site of aneurysm
  • Ggiving rise to bitemporal hemianopia
• Anterior choroidal artery -Supplies choroid plexus, optic tract, internal capsule, hippocampal formation, globus pallidus, and lateral portions of thalamus
• Anterior cerebral artery (A1-A5)
• Middle cerebral artery (M1-M4)

Anterior Cerebral Artery Branches (ACA)

• Supply the frontal pole and most of the medial and superior surfaces of the brain up to the parietooccipital sulcus
• Stroke in the distal portions can lead to sensorimotor deficit in the opposite foot and leg

Middle Cerebral Artery (MCA)

• Supplies the lateral aspect of the hemispheres, including the trunk-face-upper extremity area of the motor and sensory cortices, as well as the Broca and Wernicke speech areas A stroke in cortical distribution of the upper branch may cause a severe sensorimotor deficit in the contralateral face, trunk, and upper limb and non-fluent (Broca) aphasia.
• A stroke in the lower branch may produce fluent (Wernicke) aphasia.
• Segments M1-M4

Vertebrobasilar System

• V1-V4 segments
• Primary blood supply to the brainstem
• V4 segment is vulnerable to injury or blood flow restriction
  • Hyperextension and extreme rotation of the head can lead to injury

Arterial Supply of Cerebral Hemispheres

Cerebral Arterial Circle (Willis)

• A pentagon-shaped network of arteries at the base of the brain
• Provides collateral blood flow
• Includes the anterior cerebral, internal carotid, middle cerebral, anterior choroidal, posterior cerebral, superior cerebellar, pontine, labyrinthine, anterior inferior cerebellar, basilar, vertebral, anterior and posterior communicating and ophthalmic arteries

Clinical Notes: Cerebral Aneurysm

• Sac-like dilation, which can cause hemorrhagic stroke if ruptured
• Treatment: surgical coiling, clipping, endovascular stenting
• Cerebral embolism (e.g., blood clot): Cerebral Ischemia: Infarction: Necrosis- May cause severe neurological deficit and/or death.

Vertebral Artery Branches

• Posterior Inferior Cerebellar Artery (PICA)
  • Supplies the lateral medulla, spinothalamic tract, dorsal and ventral spinocerebellar tracts, descending sympathetic tract, CN V, and nucleus ambiguous
  • Serves the choroid plexus of the 4th ventricle
  • May arise from the vertebral artery (25%)
• Anterior Spinal Artery (ASA)
  • Medulla, pyramids, Hypoglossal nucleus, medial lemniscus, inferior olivary nucleus.
  • Supplies the ventral portion of the spinal cord
  • Hypoperfusion may manifest with weakness, loss of pain and temperature sensation, while sparing position and vibration

Basilar Artery Branches

• AICA (Anterior Inferior Cerebellar Artery) and Labyrinthine Artery
• Pontine Arteries
• Superior Cerebellar and Posterior Cerebral Arteries

Vertebral Artery Branches: Anterior Inferior Cerebellar Artery

• Supplies Pons, CN VII, and the anterior inferior surface of the cerebellum
• Hypoperfusion manifests with lateral pontine syndrome

Pontine Arteries

• Supply the base of the pons, including corticospinal fibers and the CN VI
• Hypoperfusion features the "locked-in" syndrome, where patients remain aware but are paralyzed in all muscles except those for blinking and vertical eye movement

Superior Cerebellar Artery (SCA)

• Supplies the pons, superior surface of the cerebellum, CN VII, and CN VIII
• An aneurysm can lead to compression of CN III, which manifests as a dilated pupil on the affected side

Posterior Cerebral Artery (PCA)

• Supplies the occipital lobe
• An aneurysm may be associated with CN III palsy
• Supplies : -Midbrain -Thalamus -Temporal lobes (ventral and medial surface) -Occipital
• Hypoperfusion may lead to contralateral homonymous hemianopia

The artery's Posterior cerebral P1-P4 segments

• Medial and lateral posterior choroidal and thalamogeniculate arteries originate from P2 segments.
• Vertebral artery is larger on the left than the right

Cerebral Arteries – Areas Supplied, Watersheds

• Regions of the brain that receive dual blood supply from branching endings are most vulnerable to any reduction in blood flow that may lead to watersheds infarcts (~10% ischemic strokes).
  • Anterior – contralateral hemiparesis: can lead to the lower extremity, expressive language deficits, or behavioral changes
  • Posterior – partial visual loss: Can be accompanied by language problems.

Dural Venous Sinuses

• Lined by endothelium
• Blood-filled spaces situated between the layers of the dura mater
• Walls are thick and composed of fibrous tissue.
• Have NO muscular tissue and NO valves.
• Receive tributaries from the brain, the orbit, the internal ear, and diploë of the skull
• Drains venous blood

Cerebral Veins

• Superior sagittal sinus
• Inferior sagittal sinus
• Great cerebral vein
• Straight sinus
• Confluence of sinus
• Transverse sinus
• Sigmoid sinus
• Venous drainage of the brain exits the skull through the internal jugular vein (IJV)

Great Cerebral Vein of Galen

• A single midline vein formed inside the brain by the union of the two internal cerebral veins
• Joins the Inferior sagittal sinus to form the straight sinus

Cavernous Sinus

• A collection of venous structures that surrounds the pituitary gland
• Function: drains blood from the eye, superficial cortex, and face
• Contents: CN III, IV, V1, V2, VI, internal carotid artery, and postganglionic sympathetic fibers that supply the orbit