The Ventricular System

Question 1

What is the ventricular system?

Answer 1

Series of communicating cavities in the brain

Four ventricles: two lateral ventricles, third ventricle and the 4th ventricle

Question 2

What is the shape and location of the two lateral ventricles?

Answer 2

C shaped cavities located within each cerebral hemisphere

Question 3

What is the shape and location of the third ventricle?

Answer 3

Thin vertical chamber between the thalami

Question 4

The third ventricle is continuous with the two lateral ventricles via what?

Answer 4

Th interventricular foramina and the 4th ventricle via the cerebral aqueduct

Question 5

What is the shape and location of the 4th ventricle?

Answer 5

Shaped like a four sided pyramid and located between the cerebellum and the pons

Question 6

What is the 4th ventricle continuous with?

Answer 6

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

Question 7

What is usually placed in the 4th ventricle to drain excess CSF during hydrocephalus?

Answer 7

A shunt in the cerebellomedullary cistern

Question 8

What is the flow of CSF?

Answer 8

Lateral ventricles -> interventricular foramina of Monroe -> third ventricle -> cerebral aqueduct -> 4th ventricle -> medial and lateral apertures (foramina) -> subarachnoid space

Question 9

What is the site of CSF production?

Answer 9

Choroid plexus of lateral, 3rd and 4th ventricles

Question 10

Where are choroid plexuses located?

Answer 10

Floor of lateral ventricles and roof of third and 4th ventricles

Question 11

Describe the resorption of CSF

Answer 11

Subarachnoid space of 4th ventricle -> arachnoid villi in or adjacent to superior sagittal sinus -> venous lacunae -> venous sinuses

Question 12

What is the composition of CSF?

Answer 12

Similar to blood ultrafiltrate
Higher in Na, Cl and Mg
Lower in K, Ca, glucose and protein

Question 13

What is the volume of CSF?

Answer 13

20-25mL of CSF in the ventricles and about 140mL in the system

Question 14

What is hydrocephalus?

Answer 14

An increase in cerebral mass/size due to presence of excess CSF in ventricular system, subarachnoid space or both

Question 15

What are the clinical signs of hydrocephalus?

Answer 15

Internal strabismus (abducens palsy), sundown gaze and papilledema

Question 16

What is external hydrocephalus?

Answer 16

Excess CSF in the subarachnoid space with enlargement of that space due to compression of the CNS
May be supratentorial, infratentorial or both

Question 17

What is supratentorial external hydrocephalus?

Answer 17

Associated with senile atrophy of cortex (ex. Alzheimer’s disease)

Question 18

What is infratentorial external hydrocephalus?

Answer 18

Seen in combination with communicating hydrocephalus

Question 19

What is internal hydrocephalus?

Answer 19

Aka non-communicating hydrocephalus because it does not drain into subarachnoid space

Question 20

What are the three causes of internal hydrocephalus?

Answer 20

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)

Question 21

What does internal hydrocephalus result in?

Answer 21

Dilation of ventricles proximal to the obstruction

Question 22

What is communicating hydrocephalus?

Answer 22

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)

Question 23

Describe the movement of CSF during communicating hydrocephalus

Answer 23

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

Question 24

What is the obstruction during communicating hydrocephalus caused by?

Answer 24

Adhesions and fibrosis in the subarachnoid spaces from past inflammation (e.g. infantile meningitis), cerebal edema or uncal herniation

Question 25

What does communicating hydrocephalus result in?

Answer 25

Hypertrophy of ventricles (internal hydrocephalus) and accumulation of CSF in infratentorial subarachnoid space (external hydrocephalus)

Question 26

Describe trauma to the midbrain

Answer 26

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