The Ventricular System Flashcards
What is the ventricular system?
Series of communicating cavities in the brain
Four ventricles: two lateral ventricles, third ventricle and the 4th ventricle
What is the shape and location of the two lateral ventricles?
C shaped cavities located within each cerebral hemisphere
What is the shape and location of the third ventricle?
Thin vertical chamber between the thalami
The third ventricle is continuous with the two lateral ventricles via what?
Th interventricular foramina and the 4th ventricle via the cerebral aqueduct
What is the shape and location of the 4th ventricle?
Shaped like a four sided pyramid and located between the cerebellum and the pons
What is the 4th ventricle continuous with?
The third ventricle via the cerebral aqueduct, the cerebellomedullary cistern (one of the larger subarachnoid cisterns and is a large CSF filled space above the foramen magnum) via the medial and lateral aperture/foramina, and the central canal at the obex
What is usually placed in the 4th ventricle to drain excess CSF during hydrocephalus?
A shunt in the cerebellomedullary cistern
What is the flow of CSF?
Lateral ventricles -> interventricular foramina of Monroe -> third ventricle -> cerebral aqueduct -> 4th ventricle -> medial and lateral apertures (foramina) -> subarachnoid space
What is the site of CSF production?
Choroid plexus of lateral, 3rd and 4th ventricles
Where are choroid plexuses located?
Floor of lateral ventricles and roof of third and 4th ventricles
Describe the resorption of CSF
Subarachnoid space of 4th ventricle -> arachnoid villi in or adjacent to superior sagittal sinus -> venous lacunae -> venous sinuses
What is the composition of CSF?
Similar to blood ultrafiltrate
Higher in Na, Cl and Mg
Lower in K, Ca, glucose and protein
What is the volume of CSF?
20-25mL of CSF in the ventricles and about 140mL in the system
What is hydrocephalus?
An increase in cerebral mass/size due to presence of excess CSF in ventricular system, subarachnoid space or both
What are the clinical signs of hydrocephalus?
Internal strabismus (abducens palsy), sundown gaze and papilledema
What is external hydrocephalus?
Excess CSF in the subarachnoid space with enlargement of that space due to compression of the CNS
May be supratentorial, infratentorial or both
What is supratentorial external hydrocephalus?
Associated with senile atrophy of cortex (ex. Alzheimer’s disease)
What is infratentorial external hydrocephalus?
Seen in combination with communicating hydrocephalus
What is internal hydrocephalus?
Aka non-communicating hydrocephalus because it does not drain into subarachnoid space
What are the three causes of internal hydrocephalus?
Caused by obstruction of the interventricular foramen (3rd ventricle choroid plexus ependymoma), obstruction of the cerebral aqueduct (midbrain astrocytoma) or obstruction of the medial and lateral foramina (Arnold-Chiari malformation or Dandy-Walker cyst)
What does internal hydrocephalus result in?
Dilation of ventricles proximal to the obstruction
What is communicating hydrocephalus?
Combination of infratentorial external hydrocephalus + internal hydrocephalus
Obstruction of the space between tentorial notch and the midbrain (the only communication of CSF from posterior cranial fossa to supratentorial region)
Describe the movement of CSF during communicating hydrocephalus
CSF is free to move through the ventricular system into the infratentorial subarachnoid space but it cannot circulate over cerebrum to be reabsorbed by arachnoid villi
What is the obstruction during communicating hydrocephalus caused by?
Adhesions and fibrosis in the subarachnoid spaces from past inflammation (e.g. infantile meningitis), cerebal edema or uncal herniation
What does communicating hydrocephalus result in?
Hypertrophy of ventricles (internal hydrocephalus) and accumulation of CSF in infratentorial subarachnoid space (external hydrocephalus)
Describe trauma to the midbrain
Severe blows to the head may cause the sharp edge of the incisura to lacerate or contuse the brainstem
Result: some degree of temporary or permanent coma, depending on the amount of damage to the midbrain reticular formation
