Meninges and CSF Flow

Meninges

• Meninges are membranes that surround and protect the brain and spinal cord.
• Dura mater: The outermost layer closely apposed to the skull, the inner layer forms sinuses.
• Arachnoid mater: The middle layer with cerebrospinal fluid (CSF) flowing in the subarachnoid space, does not follow sulci
  • Arachnoid trabeculae support this layer.
• Pia mater: The innermost layer closely apposed to the brain parenchyma.
• Pia + Arachnoid = leptomeninges.
• The skull is closely apposed to the dura mater.
• Spinal column is separated from the dura by the epidural space.

Periosteal Dural Infoldings

• Falx cerebri: Responsible for midline shift.
• Tentorium cerebelli: Involved in transtentorial herniation.
• Falx cerebelli
• Diaphragma sella: Covers the hypophyseal fossa; pituitary tumors can compress the hypothalamus.

Relation of Meninges to CSF Flow

• Brain: The dura is apposed to the skull.
• Arachnoid trabeculae provide support.
• Arachnoid villi (granulations) facilitate the venous return of CSF into the superior sagittal sinus.
• The sub-arachnoid space is accessible in the cisterna magnum.
• Spinal column: The dura is away from the vertebrae.
• Denticulate ligaments support the spinal cord within.
• The sub-arachnoid space is accessible in the lumbar cistern.

Meningitis

• Meningitis: Inflammation of the brain or spinal cord, can be bacterial, viral, fungal, or environmental in origin
• CSF samples are used to identify the source of meningitis.
• General signs of meningeal irritation: Nuchal rigidity, headache, fever.
• Long-term consequences: Cranial nerve palsies (II, VII, VIII), general paresis, sensory loss, and ataxia.
• Specific signs of meningeal irritation:
  • Kernig's sign: Knee straightening by a practitioner causes hamstring pain.
  • Brudzinski's sign: Neck flexion by practitioner causes hip flexion.

Head Trauma

• Head trauma can cause damage to the brain.
• Coup and counter coup injuries can occur.
• Concussion: Characterized by alteration of consciousness.
• Contusion: Involves brain tissue injury, hemorrhagic lesions, and axonal injury.
• Post-traumatic head injury can result in hydrocephalus or dementia.
• Displaced skull fracture: Occurs when skull thickness is exceeded.
• Contusions can occur in Temporal, inferior frontal, or occipital lobes.

Vascular Injury/Hematoma

• Epidural hematoma: Due to skull fracture and tearing of meningeal arteries.
• Subdural hematoma: Due to concussion/contusions, typically tearing of veins at the dural/meningeal border.
• Subarachnoid hemorrhage: Typically from ruptured aneurysm of arteries into the subarachnoid space.
• Contusion: Damage at the surface of the brain.
• Intra-parenchymal hemorrhage: Occurs within brain tissue.

Subarachnoid Cisterns

• These contain CSF samples.
• Cisterna magna, lumbar cistern
• Paracallosal, quadrigeminal, lamina terminalis, chiasmatic, ambient, interpeduncular, prepontine, premedullary
• Cisterns collect fluid in areas of cranial nerves, arteries, and veins.
• Blood in CSF from injury can be visualized by contrast.
• Useful in imaging subarachnoid hemorrhage.

Autopsy and CT Scans of Hematoma

• Epidural, subdural

CT and MRI Scans

• Shows hematoma, contusion, meningioma.
• Meningeal tumors can cause pressure against the parenchyma or brainstem and can indicate malignancy.
• Additionally can show subarachnoid or intra-parenchymal indications

Herniation

• Defined as the displacement of brain parenchyma.
• Midline shift:
  • Subfalcine herniation: The cingulate gyrus shifts under the falx cerebri, increased intracranial pressure
• Transtentorial uncal herniation: The temporal lobe moves against the tentorium
  • This damages cranial nerve (CN) III and cerebral peduncles
  • Can also cause eyemotor palsy or hemiparesis.
• Tonsillar herniation: The cerebellum moves through foramen magnum, creating pressure on the medulla of the brainstem
  • Can cause cardiac/ respiratory distress.

Case Study One

• 52-year-old male experiences headaches, left-sided weakness, and lethargy.
• MRI reveals right-side tumor identified as glioblastoma multiforme.
• The patient passes away and the family requests an autopsy.
• Autopsy confirms a tumor mass on the right side.
• Uncal herniation may affect multiple structures at the tentorial notch.
• Lethargy: reticular formation
• Weakness: cerebral peduncle

Case Study One Results

• Autopsy showed Duret hemorrhage
• Posterior cerebral artery infarction, and CN III compression

Development of Ventricles

• Ventricles are brain regions:
• The first is the three vesicle stage.
• The second is the one space stage.
• The third is the five vesicle stage.
• Expansion and Flexures:
  • Telencephalon: lateral ventricles
  • Diencephalon: third ventricle
  • Mesencephalon: cerebral aqueduct
  • Metencephalon and myelencephalon: fourth ventricle
  • Spinal cord: central canal

Ventricles and Communicating Spaces

• Lateral Ventricles: anterior horn, inferior horn, atrium, posterior horn
• Foramen of Monro (interventricular foramen)
• Third Ventricle
• Cerebral aqueduct of Sylvius
• Fourth Ventricle: foramen of Magendie & foramina of Luschka
• Central Canal

Choroid Plexus

• It produces CSF.
• Present in the lateral and fourth ventricles.
• Ventricular Exits: foramen of Magendie/foramina of Luschka

Distribution of Ventricles

• Lateral ventricles are in the cerebrum.
• The third ventricle is in the diencephalon.
• Cerebral aqueduct is in the midbrain.
• The fourth ventricle is above the medulla.
• T1 and T2 MRI: Used to visualize the ventricles I and II

Production and Flow of Cerebrospinal Fluid

• CSF Produced:
  • Choroid capillary tufts (plexus) in the lateral and fourth ventricles produce CSF responsible for buoyancy, shock absorption
• CSF Flows:
  • Through the ventricular system, into central canal, and out foramina of Magendie/Luschka
  • Throughout the subarachnoid space
• CSF Returns:
  • Through arachnoid granulations (villi) into the superior sagittal sinus
  • Fluid returns to the right side of the heart through the vena cava.

Ependyma

• It lines the ventricular cavity.
• Tanycyte end feet contact blood vessels, assist in the ventricle/blood barrier.
• Ependymoma is a childhood tumor; results in: hydrocephalus or compression of the brainstem, cranial nerve dysfunction.

Hydrocephalus

• Developmental Disorder
  • Aqueductal Obstructive Stenosis
  • CSF Production/Resorption
  • Enlargement of Cranium
• Hydrocephalus ex Vacuo
  • Loss of Parenchyma (Huntington's)
  • Enlargement of the Lateral Ventricles
• Adult Obstructive Hydrocephalus
  • Convulsions, Seizures
• Pseudotumor Cerebri
  • Hypertensive Disease, Diabetes
  • More Common in Women
  • Headaches and Nausea
• Normal Pressure Hydrocephalus
  • Remitting Increase in Intracranial Pressure
  • Symptoms: Gait Imbalance, Incontinence, Dementia

Intracranial Pressure Pathologies

• Hydrocephalus
• Hematoma
• Tumors
• Infection
• Obesity/Diabetes
• Consequences encompass compression of vasculature/hemorrhage, and parenchyma compression/edema.
• Case Study 2 - Onset and Recovery From Contusion:
  • Presentation: posterior scalp laceration, lethargy, decreased level of consciousness, right hemi-plegia and sensory loss, absent right corneal reflex

Case Study 2

• Coup/Countercoup Cerebral Contusion
• Subdural Hematoma
• Midline Shift, Pineal calcification, Subdural and Subarachnoid Hematoma
• Countercoup injury affected frontal/temporal lobes.
• Resolved lethargy level of consciousness in time.
• Resolved Hemiparesis: compression of corticospinal tract
• Corneal reflex dysfunction suggested that brainstem (tentorium) involvment

Fluid Exchange Summary

• Vascular system has arterial blood flow
  • Then is filtered by the blood brain barrier, or to the blood CSF barrier
• Flows to interstitual tissue
  • Then to intracellular cytoplasm of neurons & glia
• Next cerebral venules & veins filter CSF
• Lastly fluid and byproducts go to venous sinuses - Fluids go to superior sagittal sinus or spinal sinuses