Raised intracranial pressure
- Increase in mean CSF pressure above 200mm of water with the patient recumbent
- Occurs when the volume of brain tissue increases beyond the limit permitted by compression of veins and displacement of CSF
- Caused by;
- Mass effect;
- Brain tumour
- Infarction with oedema
- Contusion
- Haematoma
- Abcesses
- Brain tumour
- Generalised brain oedema associated with;
- severe hypoxia
- liver failure
- hypertensive encephalopathy
- severe hypoxia
- Impaired circulation or reabsorption of CSF
- Increased venous pressure due to;
- Venous sinus thrombosis
- Heart failure
- Obstruction of superior mediastinal or jugular veins
- Increased venous pressure due to;
- Obstruction to CSF flow/absorption
- Hydrocephalous
- Extensive meningeal disease – infection, carcinomatous, haemorrhagic
- Hydrocephalous
- Increased CSF production, occurs associated with;
- Meningitis
- Subarachmoid haemorrhage
- Choroid plexus tumour
- Meningitis
- Because the cranial vault is subdivided by dural folds a focal expansion of the brain causes it to be displaced in relation to these partitions resulting in herniation
Subfalcine (cingulate) herniation
- Occurs when unilateral expansion of a cerebral hemisphere displaces the cingulated gyrus under the falx cerebri
- May be associated with compression of branches of the anterior cerebral artery
Transtentorial herniation
- Occurs when the medial aspect of the temporal lobe is compressed against the free margin of the tentorium cerebelli
- May compromise the third cranial nerve
- May compress the posterior cerebral artery
- Progression of transtentorial herniation is often accompanied by haemorrhagic lesions in the midbrain and pons known as Duret haemorrhages
Tonsillar herniation
- Refers to the displacement of the cerebellar tonsils through the foramen magnum
- Causes brainstem compression and compromises respiratory and cardiac centres in the medulla