• A pressure gradient between intracranial compartments is a much greater hazard than generalized intracranial hypertension because shift of intracranial structures caused by differences in compartmental pressures can lead to compression and infarction of herniated tissue.
• A sudden change in intracranial pressure, as is seen in acute intracranial hemhorrage, may lead to acute and fulminating neurological decline.
• Tumors may cause a gradual increase in intracranial pressure, which is tolerated with few symptoms but is predisposed to rapid deterioration on slight changes in intracranial pressure with a relatively innocuous stimulus such as a cough, sneeze, or Valsalva maneuver.
• Unilateral transtentorial herniation is caused by a supratentorial mass lesion and is initially associated with an ipsilateral dilated pupil followed by decline in mental status and contralateral hemiparesis.
• Central transtentorial herniation, commonly seen in the pediatric population with hydrocephalus, is initially associated with diencephalic dysfunction and paresis of upward gaze (Parinaud's syndrome) rather than dilated pupils.
• Transforaminal herniation which presents with neck tilt or nuchal rigidity must be distinguished from subarachnoid hemorrhage and/or meningitis because diagnostic lumbar puncture and resultant decreases in spinal cord pressure can lead to further herniation and infarction of tissues as the posterior inferior cerebellar arteries are compressed at the foramen magnum.
• Upward cerebellar herniation can compress the aqueduct of Sylvius with resultant hydrocephalus and exacerbation of the process.
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