Neuroanatomy: Cerebrospinal Fluid and Brain Structures

• Lecture pertains to the meninges, trauma, ventricles, choroid plexus, CSF, hydrocephalus, and cisterns of the brain

Meninges

• The meninges are protective membranes surrounding the brain and spinal cord
• There are three layers: dura mater, arachnoid mater, and pia mater
• The dura mater is closely apposed to the skull, while the spinal column has an epidural space separating it
• The inner layer of the dura mater forms sinuses
• Cerebrospinal fluid (CSF) flows in the subarachnoid space
• The subarachnoid space does not follow the sulci of the brain
• Arachnoid trabeculae support the arachnoid mater within the subarachnoid space
• The pia mater is closely apposed to the brain parenchyma
• Together, the pia and arachnoid mater are known as the leptomeninges

Periosteal Dural Infoldings

• The periosteal dural infoldings include the falx cerebri, tentorium cerebelli, and diaphragma sella
• The falx cerebri can cause a midline shift
• The tentorium cerebelli can cause transtentorial herniation
• The diaphragma sella covers the hypophyseal fossa, which can compress the hypothalamus if there is a pituitary tumor present

Meninges and CSF Flow

• The dura mater is apposed to the skull
• Arachnoid trabeculae provide support
• Arachnoid villi (granulations) facilitate venous return of CSF into the superior sagittal sinus
• The subarachnoid space is accessible in the cisterna magnum and lumbar cistern
• The dura mater is away from the vertebrae in the spinal column
• Denticulate ligaments support the spinal cord

Meningitis

• Meningitis involves inflammation of the brain or spinal cord lining
• It can be bacterial, viral, fungal or environmental origin

General Signs of Meningeal Irritation

• Nuchal rigidity (neck stiffness)
• Headache
• Fever

Long-term Consequences of Meningitis

• Cranial nerve palsies (II, VII, VIII)
• General paresis
• Sensory loss and ataxia

Specific Signs

• Kernig's sign: straightening the knee by a practitioner causes hamstring pain in the patient
• Brudzinski's sign: neck flexion by a practitioner causes hip flexion in the patient

Head Trauma

• Trauma to the head damages the brain
• Coup and countercoup injuries can occur
• Concussion involves an alteration of consciousness
• Contusion is brain tissue injury
• Hemorrhagic lesions and axonal injury can result
• Hydrocephalus and dementia are post traumatic injuries
• Displaced skull fracture is identified when it is greater than the skull thickness

Vascular Injury - Hematoma

• Epidural hematoma: skull fracture, tearing of meningeal arteries
• Subdural hematoma: concussion/contusions, tearing of veins at the dural/meningeal border
• Subarachnoid hemorrhage: ruptured aneurysm of arteries, into the subarachnoid space
• Contusion: damage at the surface of the brain
• Intra-parenchymal hemorrhage: within brain tissue

Subarachnoid Cisterns

• The subarachnoid cisterns include the paracallosal, quadrigeminal, lamina terminalis, chiasmatic, ambient, interpeduncular (fossa), prepontine, and premedullary cistern
• They collect fluid in areas of cranial nerves and arteries
• Blood in CSF, from injury, can be visualized by contrast when imaging
• Cisterna magna and a lumbar cistern

Herniation

• Herniation is the displacement of brain parenchyma
• Midline shift happens with subfalcine herniation, where the cingulate gyrus is under the falx cerebri, leading to increased intracranial pressure
• Transtentorial uncal herniation occurs when the temporal lobe is against the tentorium, damaging CN III and cerebral peduncles, leading to eyemotor palsy and hemiparesis
• Tonsillar herniation involves the cerebellum through the foramen magnum pressing on the medulla of the brainstem, causing cardiac and respiratory distress

Case Study One

• A 52 year old male patient experienced headaches, left sided weakness, and lethargy
• MRI results: a right-sided tumor, glioblastoma multiforme, was found; the patient passed away, and autopsy results confirmed a tumor mass on the right side
• Uncal herniation can affect multiple structures at the tentorial notch

Brain Autopsy results

• Lethargy - reticular formation
• Weakness - cerebral peduncle
• Duret hemorrhage
• Posterior cerebral artery
• CN III compression

Vetricles - Development

• Vesicles are the brain regions
• There is a three and five vesicle stage
• Cerebrum arises from telencephalon
• Thalamus is from diencephalon
• Midbrain is from mesencephalon
• Pons and cerebellum are from metencephalon
• Medulla is from myelencephalon Spinal cord is the central canal

Lateral Ventricles

• Anterior horn
• Inferior horn
• Atrium
• Posterior horn

Other Ventricle information

• Foramen of Monro: interventricular foramen
• 3rd ventricle
• Cerebral aqueduct of Sylvius
• 4th ventricle: the foramen of Magendie and foramina of Luschka
• Central canal

Choroid plexus

• Production of cerebrospinal fluid

CSF Circulation

• Lateral ventricle
• Fourth ventricle exits
• Foramen of Magendie
• Foramina of Luschka

Distribution of Ventricles

• Lateral ventricles in the cerebrum
• 3rd ventricle in the diencephalon
• Cerebral aqueduct in the midbrain
• 4th ventricle above the medulla

CSF Production

• Choroid capillary tufts (plexus) - lateral and fourth ventricles
• Buoyancy and shock absorption functions

CSF Flows

• Ventricular system into the central canal and out foramina of Magendie/Luschka
• Throughout subarachnoid space

CSF Returns

• Through arachnoid granulations (villi) into the superior sagittal sinus

Ependyma

• Epithelial lining of ventricular cavity
• Tanycyte end feet that contact blood vessels, aid in ventricle/blood barrier
• Ependymoma (childhood tumor): hydrocephalus and/or compression of brainstem (cranial nerve dysfunction)

Hydrocephalus

• Developmental disorder: aqueductal obstructive stenosis, CSF production/resorption, enlargement of cranium
• Hydrocephalus "ex vacuo": loss of parenchyma (like in Huntington's), enlargement of lateral ventricles
• Adult obstructive hydrocephalus: seizures, convulsions
• Pseudotumor cerebri: hypertension, more common in women, headaches and nausea
• Normal Pressure hydrocephalus: gait imbalance, incontinence, dementia

Pathologies Affecting Intracranial Pressure

• Hydrocephalus
• Hematoma
• Tumors
• Infection
• Obesity, diabetes

Consequences

• Compression of vasculature and hemorrhage
• Compression of parenchyma and edema

Case Study 2

• The case is about the onset of recovery from contusion
• Posterior scalp laceration and lethargy
• Decreased level of consciousness
• Absent right corneal reflex
• Right hemi-plegia and sensory loss

Signs of Damage

• Affected - frontal and temporal lobes by countercoup injury
• Lethargy and level of consciousness resolved in time
• Hemiparesis from compression of corticospinal tract also resolved over the course of one year
• Corneal reflex dysfunction suggested that brainstem (tentorium) was involved

Brain and Blood Fluids

Summary of the fluid exchange from brain>blood:

• Vascular system (arterial blood)> blood brain barrier>the interstitial tissue>intracellular cytoplasm of neurons and glia
• Vascular system (arterial blood)>blood CSF barrier>CSF in ventricles and subarachnoid space>arachnoid villi
• Cerebral venules and cerebral veins leading into the venous sinuses. Including the superior sagittal sinus and superior sinuses