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
• Generalised brain oedema associated with;
  • severe hypoxia
  • liver failure
  • hypertensive encephalopathy
• Impaired circulation or reabsorption of CSF
  • Increased venous pressure due to;
  • Venous sinus thrombosis
  • Heart failure
  • Obstruction of superior mediastinal or jugular veins
• Obstruction to CSF flow/absorption
  • Hydrocephalous
  • Extensive meningeal disease – infection, carcinomatous, haemorrhagic
• Increased CSF production, occurs associated with;
  • Meningitis
  • Subarachmoid haemorrhage
  • Choroid plexus tumour

 

• 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