Meninges and Cerebrospinal Fluid (CSF)

Meninges

• These are membranes that surround and protect the brain and spinal cord.
• The dura mater closely adheres to the skull, with the inner layer forming sinuses.
• Cerebrospinal fluid (CSF) flows in the subarachnoid space within the arachnoid mater.
• The subarachnoid space doesn't follow sulci.
• Arachnoid trabeculae offer support within the arachnoid mater.
• The pia mater is closely apposed to the brain parenchyma.
• The pia mater and arachnoid together make up the leptomeninges.
• In the spinal column, the dura is separated from the vertebrae by the epidural space.

Periosteal Dural Infoldings

• Falx cerebri causes a midline shift when displaced.
• Tentorium cerebelli can cause transtentorial herniation.
• Diaphragma sella covers the hypophyseal fossa, which means pituitary tumors can compress the hypothalamus.

Relation of Meninges to CSF Flow

• In the brain, the dura is closely apposed to the skull.
• Arachnoid trabeculae support the arachnoid mater.
• Arachnoid villi granulations allow for venous return of CSF into the superior sagittal sinus.
• The subarachnoid space is accessible in cisterna magnum.
• In the spinal column, the dura is away from the vertebrae.
• Denticulate ligaments support the spinal cord.
• The subarachnoid space is accessible in the lumbar cistern.

Meningitis

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

Head Trauma

• Head trauma involves coup and countercoup injuries
• Concussion: Alteration of consciousness
• Contusion: Brain tissue injury
• Head trauma can cause hemorrhagic lesions or axonal injury
• Possible post-traumatic head injuries: Hydrocephalus and dementia
• A displaced skull fracture is characterized by a skull thickness
• Contusions can be: Temporal, inferior frontal, or occipital.

Vascular Injury/Hematoma

• Epidural hematoma usually results from a skull fracture and tearing of meningeal arteries.
• Subdural hematoma is associated with concussions/contusions and tearing of veins at the dural/meningeal border.
• Subarachnoid hemorrhage typically arises from a ruptured aneurysm of arteries into the subarachnoid space.
• Contusion causes damage at the surface of the brain
• Intraparenchymal hemorrhage occurs within the brain tissue

Subarachnoid Cisterns

• Subarachnoid cisterns include: Paracallosal, quadrigeminal, lamina terminalis, chiasmatic, ambient, interpeduncular (fossa), prepontine, and premedullary cisterns.
• Cisterna magna and lumbar cistern are sampled for CSF.
• Cisterns, which collect fluid around cranial nerves and vessels, can show injury with contrast during imaging.

Autopsy and CT Scans of Hematoma

• Autopsy and CT scans are used to identify the type of hematoma present.
• Hematomas: Epidural, subdural.

CT and MRI Imaging

• CT scans help to identify hematomas.
• MRI scans can identify meningiomas.
• Meningeal tumors can cause pressure against parenchyma and the brainstem and can be malignant.

Herniation

• Herniation is displacement of brain parenchyma.
• Subfalcine herniation: Cingulate gyrus is displaced under falx cerebri, increasing intracranial pressure.
• Transtentorial uncal herniation: Temporal lobe is compressed against tentorium, damaging CN III and the cerebral peduncles
  • eyemotor palsy and hemiparesis can occur.
• Tonsillar herniation: Cerebellum moves through foramen magnum, compressing the medulla oblongata.
  • cardiac or respiratory distress can occur.

Case Study One

• 52 year old male presents with headaches, left sided weakness and increasing lethargy
• MRI reveals R side tumor, glioblastoma multiforme.
• The patient passed away and family requested an autopsy
• Autopsy confirms R side tumor
• Uncal herniation can affect structures at the tentorial notch,

Brain Autopsy Findings in Case Study One:

• Patient symptoms included: Lethargy (reticular formation) and weakness (cerebral peduncle).
• Also observed: Duret hemorrhage, posterior cerebral artery infarction and CN III compression.

Development of Ventricles

• Vesicles develop into brain regions during neural development.
• Three vesicle stage: Key brain regions start differentiating.
• A single space transforms into a complex ventricular system.
• At five vesicle stage, regions further refine.
• Telencephalon forms the lateral ventricles.
• Diencephalon forms the third ventricle.
• Mesencephalon forms the cerebral aqueduct.
• Metencephalon and myelencephalon form the fourth ventricle.
• The spinal cord develops a central canal.

Ventricles

• Lateral Ventricles are ventricles which include an anterior, inferior and posterior horn with an atrium.
• Foramen of Monro is also known as the interventricular foramen
• There is a third ventricle
• The cerebral aqueduct of Sylvius is present.
• The fourth ventricle has a foramen of Magendie and foramina of Luschka
• There is a central canal.

Choroid Plexus and CSF

• Choroid plexus produces CSF
• Lateral and fourth ventricle contain the choroid plexus
• CSF circulates the ventricular system
• CSF exits the ventricular system through foramen of Magendie and foramina of Luschka

Distribution of Ventricles

• Lateral ventricles are in the cerebrum.
• Third ventricle is in the diencephalon.
• Cerebral aqueduct is in the midbrain.
• Fourth ventricle is above the medulla.
• T1 and T2 MRI can be used to visualize the ventricles.

Production and Flow of CSF

• CSF is produced by choroid capillary tufts (plexus) in the lateral and fourth ventricles.
• CSF functions in buoyancy and shock absorption, protecting the brain.
• CSF flows: Into the ventricular system, into the central canal, and out foramina of Magendie/Luschka.
• Second, CSF flows throughout the subarachnoid space.
• CSF returns through arachnoid granulations (villi) into the superior sagittal sinus.
• The fluid returns to the right side of the heart.

Ependyma

• Ependyma is the epithelial lining of ventricular cavity
• Tanycyte end feet contact blood vessels.
• They help in ventricle / blood barrier
• Ependymoma is a childhood tumor
  • Consequences include: Hydrocephalus and / or compression of brainstem - cranial nerve dysfunction

Hydrocephalus

• Hydrocephalus can be caused by developmental disorders, especially aqueductal obstructive stenosis
• CSF production / resorption
• Leads to enlargement of the cranium
• Hydrocephalus ex vacuo: Loss of parenchyma (Huntington's) can cause enlargement of lateral ventricles
• Adult obstructive hydrocephalus causes convulsions and seizures
• Pseudotumor cerebri occurs with hypertensive disease/diabetes, especially in women, and comes with headaches and nausea
• Normal Pressure hydrocephalus presents with remitting increase in intracranial pressure and symptoms such as gait imbalance, incontinence, and dementia

Intracranial Pressure

• Pathologies affecting intracranial pressure: Hydrocephalus, hematoma, tumors, infection, obesity, and diabetes.
• Consequences of increased intracranial pressure: Compression of vasculature/hemorrhage and compression of parenchyma/edema
• A sign of pressure is posterior scalp laceration, lethargy, decreased level of consciousness, right hemi-plegia and sensory loss right corneal reflex.
• Factors in Case Study 2 include: Coup/countercoup cerebral contusion, subdural hematoma, midline shift, and falx cerebri/tentorium cerebelli.

Reactive Gliosis

• Follow up is key, in instances of traumatic and increased intracranial pressure
• Countercoup injury can affect frontal and temporal lobes.
• The level of lethargy and consciousness should resolved in time
• Hemiparesis from compression of corticospinal tract also resolves over course of approximately one year.
• Corneal reflex dysfunction may indicate brainstem involvement.

Brain to Blood Fluid Exchange

• Vascular system - arterial blood
• The arterial blood goes to the blood brain barrier, and the blood CSF barrier
• Interstitial tissue interacts with intracellular cytoplasm of neurons and glia
• This runs to cerebral venules, cerebral veins
• Which allows fluid to empty in to venous sinuses, the superior sagittal sinus, and then spinal sinuses