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A 38-year-old female tobacco smoker with no significant past medical history presents with sudden new-onset bifrontal headache. The patient describes sharp, constant frontal pain with nausea, photophobia, and neck stiffness. Noncontrast CT head and clinical examination reveal acute subarachnoid hemorrhage (SAH) with Hunt and Hess grade II, Fisher group 3, and modified Fisher group 4 with bilateral intraventricular hemorrhage (IVH). An emergent ventricular drain was placed when patient's mental status deteriorated to drowsy, difficult-to-arouse state along with radiographic evidence of worsening IVH and hydrocephalus.

What are the conditions associated with abnormally elevated intracranial pressure (ICP)?

Table 12-1 lists different classifications of medical conditions that are associated with high ICP. In a neurologic intensive care unit (NeuroICU, NICU) setting, common conditions that are frequently associated with elevated ICP include acute aneurysmal high-grade SAH, severe traumatic brain injury (TBI), large intraparenchymal hemorrhage either spontaneous (such as hypertensive bleed) or in the setting of underlying coagulopathy (atrial fibrillation on warfarin therapy or coronary artery disease with cardiac stents on dual-antiplatelet therapy), malignant middle cerebral artery infarction with herniation, and severe meningitis and/or encephalitis. Although medical centers around the country have different patient populations, a great majority of all NICU cases with high ICP would fall into one of these conditions, with severe TBI being the most common etiology for intracranial hypertension1 at an annual incidence estimated to be 200 cases per 100,000 people.2

Table 12-1.Conditions Associated with Increased Intracranial Pressure

Describe the pathophysiology of ICP elevation and pathologic ICP waveforms reported in the current literature

Monro-Kellie Hypothesis

The Monro-Kellie hypothesis is a widely accepted concept for explaining the elevation of ICP. In 1783, Alexander Monro first articulated this in his Observations on the Structure and Function of the Nervous System, and later was supported by Kellie in 1824 by his observation in two humans: “Appearances observed in the dissection of two individuals; death from cold and congestion of the brain.” The hypothesis explains that the human cranium has a fixed amount of space with three main components: cerebrospinal fluid (CSF), brain parenchyma, and blood. If any space-occupying lesion or any of these constituents' volumes are increased beyond the compliance, an elevation of ICP is inevitable.3

Intracranial Compliance

Intracranial compliance is defined as the change in volume over the change in pressure ...

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