Ventricular System and CSF of the Brain

Ventricular System of the Brain

• The ventricular system of the brain is made up of four ventricles: two lateral ventricles, the third ventricle, and the fourth ventricle.
• The lateral ventricles are located in the cerebrum (telencephalon), the third ventricle is in the diencephalon, and the fourth ventricle is in the pons and medulla oblongata (rhombencephalon).
• The lateral ventricles communicate with the third ventricle via the interventricular foramina of Monro, the third ventricle communicates with the fourth ventricle via the aqueduct of Sylvius, and the fourth ventricle communicates with the cisterns of the cranial subarachnoid space via three apertures: foramen of Magendie and two foramina of Luschka.
• The cranial subarachnoid space is continuous with the spinal subarachnoid space which ends at approximately the 2nd sacral vertebral of the spinal cord.

Cerebral Spinal Fluid (CSF)

• CSF is the “lymph” of the brain.
• CSF contains a number of electrolytes and substances including lactate, cholesterol, and uric acid.
• The normal protein content in CSF is less than 4 mg/L compared to that of serum which is about 6000 mg per litre.
• CSF protein can become elevated in pathological conditions like meningitis, potentially leading to blockage of shunts used in hydrocephalus treatment.
• The normal CSF volume is around 50 mL in infants and 150 mL in adults.
• The majority of CSF is extra-ventricular in the subarachnoid space: 25 mL in the ventricular system, 100 mL in the cranial subarachnoid space, and 25 mL in the spinal subarachnoid space.
• Normal CSF pressure is about 60-150 mm of H2O.
• CSF is formed by ependymal cells of the choroid plexus of the ventricles, mainly the lateral ventricles, at a rate of approximately 550-600 mL per day.
• CSF circulation is due to a pressure gradient between the ventricular system and the venous system.
• CSF is primarily absorbed via the arachnoid villi (arachnoid granulations), which are arachnoid mater protrusions that perforate the dura mater to empty CSF into the dural venous sinuses.
• Functions of CSF include: protecting the central nervous system, providing nutrition to and removing waste products from the CNS, and lightening the weight of the brain via buoyancy.

Applied Anatomy

• Hydrocephalus
• Lumbar puncture
• Spinal anaesthesia

Hydrocephalus

• Hydrocephalus is a disturbance of CSF formation, flow, or absorption, leading to an abnormal accumulation of CSF in the ventricles of the brain.
• Hydrocephalus can be classified according to its underlying pathology: communicating hydrocephalus (non-obstructive) or non-communicating (obstructive) hydrocephalus.
• Hydrocephalus can also be classified as congenital or acquired.

Communicating Hydrocephalus

• In communicating hydrocephalus, there is no reabsorption of CSF into the dural venous sinuses.
• It can occur due to subarachnoid hemorrhage (SAH) or congenital absence of arachnoidal granulation.
• This results in CSF accumulation within the subarachnoid space, compressing brain tissue and potentially leading to brain atrophy and long-term mental retardation.

Non-Communicating Hydrocephalus

• Non-communicating hydrocephalus typically involves a blockage within the ventricular system.
• This blockage results in CSF accumulation within the ventricular system, pushing brain matter outwards against the skull.

Causes of Non-Communicating Hydrocephalus

• TORCHES
• Mass lesions: abscess, haematoma, tumours
• Aqueductal stenosis
• Dandy Walker Malformation (DWM): characterized by a prominent occiput due to cystic expansion of the 4th ventricle in the posterior cranial fossa and midline cerebellar hypoplasia resulting from developmental failure of the 4th ventricle during embryogenesis.
• Arnold Chiari Malformation type II (ACM-II): characterized by a shortened occiput where portions of the cerebellum and brainstem herniate into the cervical spinal canal, blocking CSF flow to the posterior cranial fossa.

Causes of Communicating Hydrocephalus

• Meningitis (TB)
• Subarachnoid haemorrhage (SAH)
• Meningeal malignancy
• Absence of arachnoid granulations
• Choroid plexus papilloma
• Basilar impression
• Achondroplasia (due to increased dural venous sinus pressure)

Questions to Establish Diagnosis

• Perinatal:
  • Was the child born at term or preterm?
  • Did the child cry immediately after birth?
  • What was the head circumference at birth?
  • Any abnormality of the spine?
• Post-natal:
  • At what age did the caregiver notice the head getting bigger?
  • Did the child have any fever before the head started getting big?
  • What treatment was given and for how long?
  • Any history of convulsions?
  • Any similar illness in the siblings?

Clinical Presentation of Hydrocephalus

• Infants:
  • Poor feeding
  • Irritability
  • Reduced activity
  • Vomiting
  • Drowsiness
• Children and adults:
  • Cognitive deterioration
  • Headaches (initially in the morning)
  • Neck pain, suggesting tonsillar herniation
  • Vomiting, more significant in the morning
  • Blurred vision: a consequence of papilledema and, later, of optic atrophy
  • Double vision: related to unilateral or bilateral sixth nerve palsy
  • Difficulty in walking due to spasticity: more in the lower limbs because the periventricular pyramidal tract is stretched by the hydrocephalus

Signs of Hydrocephalus

• Infants:
  • Head enlargement (head circumference ≥98th percentile for age)
  • Separation (dysjunction) of sutures
  • Dilated scalp veins
  • Delayed closure of the anterior fontanelle and will be tense
  • Positive Macewen’s sign
  • Sun-setting eye sign (characteristic of increased intracranial pressure (ICP); downward deviation of ocular globes, retracted upper lids, visible white sclerae above iris)
  • Increased limb tone (spasticity preferentially affects the lower limbs)
• Children and adults:
  • Papilledema
  • Failure of upward gaze
  • Unsteady gait
  • Large head
  • Unilateral or bilateral sixth nerve palsy (secondary to increased ICP)

Work Up for Hydrocephalus

• Laboratory:
  • No specific blood tests are recommended
  • Genetic testing and counselling are recommended when X-linked hydrocephalus is suspected
  • CSF evaluation is recommended in post-hemorrhagic and post-meningitic hydrocephalus to exclude residual infection.
• Imaging:
  • Skull X-ray (calcifications, thin skull bones, separation of sutures, beaten copper appearance (BCA))
  • CT/MRI head
  • EEG (when seizures are present)

Treatment

• Surgery is the mainstay of treatment.
• Medical Treatment is controversial.
• Acetazolamide and Furosemide are medications that decrease CSF secretion by the choroid plexus.
• Isosorbide is a medication that increases CSF reabsorption, but its effectiveness is questionable.
• Medical treatment may be used as a temporary measure to treat post-hemorrhagic or post-meningitic hydrocephalus in neonates to delay surgical intervention.

Surgical Treatment

• Surgical treatment is the preferred therapeutic option for hydrocephalus.
• Shunting is the most common option:
  • Ventriculoperitoneal (VP) shunt: The most commonly used shunt. The lateral ventricle is the usual proximal location. A long peritoneal catheter helps obviate the need to lengthen the catheter with growth. This reduces repeated lengthening in a growing child.
  • Ventriculoatrial (VA) shunt: Also called a "vascular shunt". It shunts the cerebral ventricles through the jugular vein and superior vena cava into the right cardiac atrium. It is used when the patient has abdominal abnormalities like peritonitis, morbid obesity, or has undergone extensive abdominal surgery. This shunt requires repeated lengthening in a growing child.
  • Lumboperitoneal shunt: Only used for communicating hydrocephalus, CSF fistula, and pseudotumor cerebri.
  • Ventriculopleural shunt: Less commonly used than VP shunts, it drains CSF into the pleural space.
  • Torkildsen shunt: Rarely used. It shunts the ventricle to the cisterna space and is effective only in acquired obstructive hydrocephalus.
• Endoscopic third ventriculostomy (ETV): A minimally invasive procedure involving a small hole in the floor of the third ventricle to allow for the free flow of CSF into the subarachnoid space. This option is particularly useful for cases of communicating hydrocephalus.

Shunting

• The principle of shunting is to establish communication between the CSF (ventricular or lumbar) and a drainage cavity (peritoneum, right atrium, pleural cavity).
• Shunting is not perfect, and all alternatives should be considered first.

This quiz explores the ventricular system of the brain and the role of cerebrospinal fluid (CSF). It covers the anatomy of the brain's ventricles, their connections, and the importance of CSF in brain function and protection. Test your knowledge on these critical neuroanatomy concepts.