Neurology: Hydrocephalus, Abnormal Head Shapes & Muscular Dystrophy Flashcards
What is hydrocephalus?
Describes CSF building up abnormally within the brain and spinal cord.
This is a result of either:
a) over production of CSF, or
b) problem with draining or absorbing of CSF
How many ventricles are there in the brain?
4:
- two lateral
- the third
- the fourth
What is CSF produced by?
The 4 choroid plexuses (one in each ventricle) and by the walls of the ventricles.
What is CSF absorbed by?
Absorbed into the venous system by the arachnoid granulations.
What is the most common cause of congenital hydrocephalus?
Aqueductal stenosis –> leads to insufficient drainage of CSF.
What is aqueductal stenosis?
The cerebral aqueduct that connects the third and fourth ventricle is stenosed (narrowed).
This blocks the normal flow of CSF out of the third ventricle, causing CSF to build up in the lateral and third ventricles.
Where does CSF build up in aqueductal stenosis?
3rd ventricle & lateral ventricles
What can hydrocephalus be broadly divided into?
1) Obstructive (‘non-communicating’) hydrocephalus
2) Non-obstructive (‘communicating’) hydrocephalus
What is obstructive (‘non-communicating’) hydrocephalus?
Due to a structural pathology blocking the flow of CSF.
Dilatation of the ventricular system is seen superior to site of obstruction.
Give some causes of obstructive hydrocephalus
- tumours
- acute haemorrhage (e.g. SAH or intraventricular haemorrhage)
- developmental abnormalities (e.g. aqueduct stenosis).
What is non-obstructive hydrocephalus?
Due to an imbalance of CSF production and absorption.
Causes of non-obstructive hydrocephalus
1) an increased production of CSF (e.g. choroid plexus tumour - very rare
2) failure of reabsorption at the arachnoid granulations (e.g. meningitis or post-haemorrhagic) - more common
What is normal pressure hydrocephalus?
A unique form of non-obstructive hydrocephalus characterised by large ventricles but normal intracranial pressure.
What classic triad of symptoms is seen in normal pressure hydrocephalus?
1) dementia
2) urinary incontinence
3) disturbed gait
give 4 causes of congenital hydrocephalus
1) aqueductal stenosis
2) arachnoid cysts: can block the outflow of CSF if they are large enough
3) Arnold-Chiari malformation
4) chromosomal abnormalities and congenital malformations can cause obstruction to CSF drainage.
What is the Arnold-Chiari malformation?
Where the cerebellum herniates downwards through the foramen magnum, blocking the outflow of CSF
What causes an enlarged and rapidly increasing head circumference (occipito-frontal circumference) in babies with hydrocephalus?
The cranial bones in babies are not fused at the sutures until around 2 years of age. Therefore, the skull is able to expand to fit the cranial contents.
When a baby has hydrocephalus it causes outward pressure on the cranial bones.
Presentation of congenital hydrocephalus?
1) Enlarged and rapidly increasing head circumference
2) Bulging anterior fontanelle
3) Poor feeding and vomiting
4) Poor tone
5) Sleepiness
6) If severe: failure of upward gaze (‘sunsetting’ eyes) due to compression of the superior colliculus of the midbrain
1st line imaging in hydrocephalus?
CT head
Investigations in hydrocephalus?
1) CT head
2) MRI head: may be used to investigate hydrocephalus in more detail
3) Lumbar puncture: both diagnostic and therapeutic (allows you to sample CSF, measure the opening pressure, and also to drain CSF to reduce the pressure)
What is the mainstay of treatment for hydrocephalus?
Ventriculoperitoneal (VP) shunt
What does a VP shunt involve?
This shunt drains CSF from the ventricles into another body cavity (usually the peritoneal cavity).
When should a LP not be done in hydrocephalus?
In obstructive hydrocephalus –> the difference of cranial and spinal pressures induced by the drainage of CSF will cause brain herniation.
Where is CSF diverted to with a ventriculoperitoneal shunt?
Peritoneal cavity