Hydrocephalus

Question 1

What is the normal adult volume in MLS of Cerebrospinal fluid?

Answer 1

150ml

Question 2

Where is the CSF absorbed

Answer 2

Via the subarachnoid granulations of the cranial venous sinuses

Question 3

Describe the Passage of CSF

Answer 3

CSF is produced in the ependymal cells of the choroid plexus in the lateral ventricles

It leaves the lateral ventricles via the foramen of Monro, travelling to the 3rd ventricle

From there, it traverses the aqueduct of Sylvius from the 3rd into the 4th ventricle

From the 4th ventricle, it either travels via the foramina of Luschka laterally into the subarachnoid space OR via the foramen of Magendie medially toward the spinal cord

Question 4

What are the non-congenital causes of hydrocephalus?

Answer 4

Communicating:

After subarachnoid or intracerebral haemorrhage
Choroid Plexus Papiloma
Following Intracerebral infection

Non Communicating:

Intracerebral tumour
Post Inflammatory adhesions
Cerebellar Haematoma or infarct

N.B. Communicating vs Non-communicating causes relate to whether or not there is an obstruction in CSF flow (as in non-communicating = obstruction in flow and communicating could be, for example, as a result of interference with absorption.

Question 5

What are the congenital causes of hydrocephalus?

Answer 5

Communicating:

Achondroplasia
Craniofacial or skull base abnormalities

Non-Communicating:

Aqueduct stenosis
Chiari Malformations
Dandy Walker Malformation

N.B. Communicating vs Non-communicating causes relate to whether or not there is an obstruction in CSF flow (as in non-communicating = obstruction in flow and communicating could be, for example, as a result of interference with absorption.

Question 6

What are the clinical features of acute Hydrocephalus

Answer 6

Headache
Impaired concious level
Vomitting
Seizures
Diplopia or Ophthalmoplegia (the paralysis or weakness of the eye muscles)
Bulging fontanelle in infants

Question 7

Describe how you would zero and commence use of an external ventricular drain (EVD)

Answer 7

Adjust the height of the pressure scale so that the zero mark is level with the foramen of Monro, which is the external acoustic meatus in the supine position with the head in the neutral position.

It is between the eyebrows in a patient in the lateral position

The CSF collection chamber is positioned in relation to the pressure scale, depending on the desired ICP.

This allows CSF in excess of a certain pressure to be collected and delivered to a drainage bag

The system must be re-zeroed if the patient’s position changes

Clamping of the drain should be avoided, particularly in patients who are dependent on CSF drainage to avoid deleterious rises in ICP

Question 8

What complications are associated with EVDs

Answer 8

Failure of the EVD to control hydrocephalus / ICP
Intracerebral haemorrhage
Seizures
Excessive CSF drainage >20ml/hr can lead to ventricular collapse or subdural haemorrhage
Catheter complications i.e. blockage, displacement, kinking
Catheter infection (antibiotic prophylaxis is usual, but infection occurs in up to 20% and often requires prolonged therapy)

Question 9

List specific anaesthetic considerations for a patient with an indwelling ventricular shunt for hydrocephalus presenting for general surgery

Answer 9

Assessment for any signs of raised ICP before and after surgery

Consider transfer to a neurosurgical centre for patients with a VP shunt and significant intrabdominal infection

Care with regional anaesthesia for upper limb surgery, as most shunts are tunneled behind the ear or behind the border of the sternocleidomastoid.

Care with positioning to prevent external pressure on the tunneled part of the shunt

Minimisation of the duration and pressure of laparoscopic surgery (although shunts do now have a one-way pressure valve)

Visualisation by the surgeon at the end of the procedure that the tip of the shunt is still draining (where this is possible)

Avoidance of internal jugular and possibly subclavian access for a patient with an indwelling ventriculo-atrial shunt

IPPV can cause blockage of an indwelling ventriculopleural shunt and should be considered in a slow-to-wake patient

Lower respiratory tract infection in a patient with a ventriculopleural shunt should be avoided, and hence post-operative physio and incentive spirometry may be useful

N.B. Indwelling ventricular shunts for hydrocephalus may include ventriculoperitoneal (VP), Ventriculo-atrial (VA), ventriculopleural, and lumbar peritoneal shunts. The major considerations when a patient with such a shunt is having other surgery are to avoid shunt damage and infection