Neuromuscular Lectures Part 3: CSF, Angiograms, and Venograms

Barriers Protecting the Central Nervous System

  • The central nervous system is protected by three barriers:
    • Blood-brain barrier
    • Blood-meninges barrier
    • Blood-CSF barrier

CSF Production and Circulation

  • CSF is produced rapidly, second only to kidney filtration.
  • There is approximately 150 mL of CSF circulating in the brain and spinal cord.
  • About 500 mL of CSF is produced every 24 hours.
  • CSF is recirculated and filtered 3-4 times per day.
  • 80% of CSF is produced by the choroid plexus.
  • 20% of CSF comes from the lining of the ventricles.
  • The surface area involved in producing CSF is approximately 20 square meters.

Blood-Brain Barrier

  • Capillaries in the brain have tightly connected endothelial cells, unlike peripheral capillaries which have spaces for diffusion.
  • Structural proteins called tight junctions hold the endothelial cells together.
  • Substances must pass through phospholipid membranes to cross the blood-brain barrier.
  • Astrocytes wrap around capillaries for an added barrier.
  • The blood-brain barrier prevents harmful substances like amino acids from entering the brain and causing seizures.
  • Receptors on endothelial cells facilitate the uptake of necessary substances and waste products.

Blood Meninges Barrier

  • Meninges consist of three layers:
    • Dura mater (collagen and connective tissue proteins)
    • Arachnoid membrane (spider web-like appearance)
    • Pia mater (thin membrane clinging to the cerebral cortex)
  • The subarachnoid space contains CSF and veins.
  • The meninges extend down to the sacrum, while the spinal cord ends at L1.
  • Inflammation of the meninges leads to meningitis.

Blood-CSF Barrier

  • The blood-CSF barrier is formed by capillaries, astrocytes, and ependymal cells, creating a three-cell barrier.
  • This barrier produces a highly purified CSF.

Ventricular System

  • The ventricular system includes:
    • Lateral ventricles
    • Foramen of Monro (connects lateral to third ventricle)
    • Third ventricle (near thalamus and hypothalamus)
    • Cerebral aqueduct of Sylvius (connects third to fourth ventricle)
    • Fourth ventricle
    • Central canal of the spinal cord
    • Lateral apertures of Luschka
    • Median aperture of Magendie
  • Obstruction of the aqueduct of Sylvius can cause hydrocephaly of the third and lateral ventricles.
  • A cerebellar tumor can compress the fourth ventricle, leading to dilation upstream.

Choroid Plexus

  • The choroid plexus is present in all ventricles.
  • It consists of endothelial cells with tight junctions, astrocytes, and cuboidal ependymal cells.
  • The choroid plexus filters fluid to produce a highly purified CSF under pressure.
  • The pressure decreases as fluid moves through the ventricular system to the jugular vein.
  • Arachnoid villi push CSF from the subarachnoid space into the superior sagittal sinus.

Meningitis

  • Meningitis is the inflammation of the meningeal tissues, causing symptoms like high temperature rash, vomiting, and difficulty breathing.
  • Two major types of meningitis:
    • Bacterial
    • Viral
  • Normal CSF values:
    • Clear color
    • Pressure: 100-200 mm Hg
    • Few cells (lymphocytes)
    • Low protein
    • Glucose: two-thirds of serum blood glucose
    • Low lactic acid
  • Viral Meningitis:
    • Increased pressure
    • Clear or slightly cloudy fluid
    • High CD8 cytotoxic lymphocytes
    • High protein
    • Normal glucose and lactate
    • Slow and progressive
  • Bacterial Meningitis:
    • Very high pressure
    • Turbulent and pus-filled CSF
    • Lots of neutrophils
    • Very low glucose
    • Elevated lactic acid
    • Rapid onset, potentially leading to seizures or coma
  • CSF can be used to identify brain tumors through secreted biomarkers.

Solute Movement Across the Blood-CSF Barrier

  • Waste products, small ions, and amino acids can move back into capillaries due to concentration gradients.
  • Ions, minerals, electrolytes, vitamins, organic nutrients, hydrophobic substances, and oxygen can leave.
  • Carbon dioxide can go back in.

Managing Intracranial Pressure

  • Normal intracranial pressure: 7-15 mm Hg (supine position)
  • Treatments for high intracranial pressure:
    • Ventriculostomy: Catheter inserted into ventricle to drain fluid
    • Bone flap removal: Cutting through the bone to allow the brain to swell, with the bone stored in the patient's abdomen. This helps to reduce pressure, blood can be reoxygenated, and swelling is reduced.
    • Mannitol IV: Osmotically draws water into the venous system, restoring osmotic balance.

Causes of Intracranial Pressure Elevation

  • Tumors
  • Subdural hematoma
  • Cerebral edema
  • Brain injury leads to ischemia and increased intracranial pressure.
  • The body compensates by increasing blood pressure, which can be counterproductive.

Case Study: Four-Year-Old Child

  • Two-week history of neck pain and unsteady gait
  • Head tilt to the left, vomiting, sudden deterioration in consciousness
  • Papilledema, truncal ataxia, sixth cranial nerve palsy, nuchal rigidity
  • A mass in the cerebellum was detected via CT Scans.
  • Treatment: Shunt to drain excess fluid, steroids to reduce inflammation, and resection of the tumor.

Pathogens Entering the Brain

  • Inflammation (cerebral edema) can breach the blood-brain barrier, leading to brain abscesses.
  • Streptococcus pneumoniae secretes pneumolysin, degrading astrocytes and endothelial cells.
  • Other microorganisms enter through junctions or hitch a ride in white blood cells.

Venous Drainage

  • Visualized via venograms involving the injection of a contrasting agent into the carotids.
  • Superior sagittal sinus, inferior sagittal sinus runs above the corpus callosum and transverse sinuses are embedded in the tentorium cerebelliare are key structures.
  • The torcula heterophili (venous confluence) is where the sinuses converge.
  • Superficial veins are shown on venograms. Arteries go deep to superficial.

Arterial Flow

  • Afferent blood flow: Aorta to the circle of Willis
  • Efferent blood flow: Circle of Willis to brain regions
  • Angiogram: Done first, contrast dye collected in the venous system
  • Deep to superficial scan