CNS causes of headache
The term hydrocephalus is used to describe conditions in which there is enlargement of the cerebral ventricles due to an increase in the CSF volume within the ventricles and CSF spaces.
Hydrocephalus can be divided into obstructive/non-communicating hydrocephalus, in which there is a blockage of the passage of the CSF within or between the ventricles, and communicating hydrocephalus, in which there is impaired resorption of the CSF in the subarachnoid space.
Obstructive hydrocephalus: One or more cerebral ventricles may be dilated, depending on the site of obstruction.
· Primary or secondary tumours of the posterior fossa or brain stem.
· Subarachnoid haemorrhage, head injury and meningitis.
· Aqueductal stenosis.
· Cerebral haemorrhage, abscesses or cysts. Communicating hydrocephalus:
· Normal pressure hydrocephalus – there is interference with the normal flow and resorption of CSF in the subarachnoid space. It may be associated with previous subarachnoid haemorrhage or meningitis, but usually there is no cause found.
· Intracranial venous thrombosis
· Basilar meningeal disease affecting the subarachnoid space.
Normally, CSF produced in the choroid plexus of the lateral ventricles flows through the foramen of Monro into the slit like third ventricle and then through the narrow aqueduct of the upper brain stem. It then flows into the fourth ventricle, where there are three apertures which allow the CSF to drain into the subarachnoid space. It flows over the surface of the brain and spinal cord and is normally reabsorbed through the arachnoid villi into the cerebral veins.
In acute hydrocephalus the raised intracranial pressure results in headache, vomiting, gait apraxia and disturbance in consciousness.
In chronic or less acute hydrocephalus signs and symptoms include headache (typically present on waking, made worse by coughing, straining or sneezing), vomiting and papilloedema. Any shift in the cranial contents can produce a variety of signs and symptoms including focal neurological signs, e.g. sixth nerve palsy.
Normal pressure hydrocephalus presents with one or more of dementia, ataxia and urinary incontinence.
Raised intracranial pressure may lead to cerebral oedema, bradycardia and hypertension. Compression of the medulla due to cerebral herniation (coning) causes impaired consciousness, respiratory depression and death.
Lumbar puncture is contraindicated in obstructive hydrocephalus due to the risk of coning. CT brain should be performed in attempt to identify the enlarged ventricles and to differentiate between communicating and non-communicating hydrocephalus. In normal pressure hydrocephalus, if removal of CSF by LP improves symptoms and signs, patients may benefit from CSF shunting.
In all cases, treatment is aimed at the underlying cause. However, emergency treatment to reduce intracranial pressure and maintain cerebral perfusion may be required:
General measures include ensuring good oxygen supply, avoiding hypercapnia, and maintaining systemic blood pressure. Steroids and mannitol are used in certain circumstances.
Drainage of the ventricles is achieved by a frontal burr hole and extraventricular drain, which also allows intracranial pressure monitoring.
If the blockage is not amenable to surgical correction a ventricular shunt may be inserted. A catheter is introduced into the lateral ventricle and tunnelled subcutaneously into the neck and into the peritoneal cavity. The shunt has a one way valve but blockage leads to an acute hydrocephalus. Shunts may become infected.