Increased Intracranial Pressure (ICP)

Overview

Definition

Pathologically increased ICP is a pressure ≥ 20 mm Hg.

Etiology

• Traumatic brain injury (TBI)/diffuse axonal injury
• Intracranial hemorrhage
  • Ruptured aneurysm
  • Arteriovenous malformations (AVMs)
• Mass lesions
  • Tumor
  • Hematoma
    • Subdural
    • Epidural
• CNS infections
  • Encephalitis
  • Brain abscess
• Ischemic stroke
• Vasculitis
• Increased CSF production
  • Hydrocephalus
  • Choroid plexus papilloma
• Hypertensive encephalopathy
• Idiopathic intracranial hypertension (pseudotumor cerebri)
• Decreased CSF absorption 
  • Communicating hydrocephalus
  • Arachnoid granulation adhesions after meningitis
  • Subarachnoid hemorrhage (SAH)

Pathophysiology

Increased ICP may be due to various clinical conditions. Brain edema or obstruction of CSF outflow may result in herniation and death.

Normal physiology

• The cranial vault is a rigid container filled with 3 components:
  • Brain parenchyma
  • CSF
  • Blood
• Monro-Kellie doctrine: if 1 component ↑, the others must ↓ proportionately to keep ICP stable
• Cerebral perfusion pressure (CPP) = mean arterial pressure (MAP) minus ICP
• Cerebral autoregulation: maintains CPP between 50 and 150 mm Hg 

Pathophysiology

• Accumulation of fluid in the brain (extracellular space) due to:
  • TBI
  • Stroke
  • Tumors
  • Infection
• Cerebral edema/relative volume of brain tissue increase → ICP ↑ and outweighs cerebral autoregulation → CPP decreases → ischemic damage
• Increased pressure on the brainstem → irregular respiration; possible herniation

Types of cerebral edema

• Vasogenic: due to increased capillary permeability resulting in extracellular fluid
  • Neurons are not primarily injured.
  • Seen with:
    • Space-occupying lesions: tumors, abscesses, intracranial hematomas
    • CNS infections
    • Infarcts
• Cytotoxic: intracellular swelling due to direct cell injury (e.g., TBI)
• Interstitial: due to increased CSF hydrostatic pressure (e.g., hydrocephalus) 
• High-altitude cerebral edema (HACE): both cytotoxic and vasogenic

Mechanisms of cerebral edema

Extracellular:

• Vasogenic edema (most common): 
  • Increased permeability of the blood–brain barrier (BBB) → exudation of a plasma ultrafiltrate into the extracellular space
  • Seen in acute ischemic brain injury and CNS tumors
• Interstitial edema (hydrocephalic): increased CSF pressure → leakage of CSF from the intraventricular space into the cerebral parenchyma

Intracellular:

• Cytotoxic edema: 
  • Depletion of energy and metabolites → dysfunction of Na/K ATPase → accumulation of Na and anions in neurons and glial cells → increased intake of water due to ionic gradient (cellular swelling)
  • Seen with TBI and acute ischemic brain injury
• Osmotic edema:
  • Increased fluid absorption by neural cells due to osmolarity gradient between cerebral parenchyma and intravascular space 
  • Seen with hyponatremia and diabetic ketoacidosis (DKA)

Abnormal posturing

• Decorticate (flexion) or decerebrate (extension) posturing
• Results from a disconnection between the modulatory higher centers and the cerebellar vestibular nuclei
• May be due to the progression of a central herniation: compression advancing from the diencephalon to the brainstem → decorticate to decerebrate posturing
• Decerebrate posturing can also be seen with severe/correctable metabolic abnormalities not due to elevated ICP:
  • Electrolyte abnormalities
  • Hypoglycemia
  • Infection

Diagnosis

Diagnosis is urgent for a patient presenting with symptoms and signs of increased ICP. Increased ICP is a medical emergency regardless of the cause, and immediate measures to reduce ICP acutely should be started until definitive management can be accomplished.

• Urgent neuroimaging: brain CT or MRI
  • Signs of brain edema:
    • Loss of gray/white matter differentiation
    • Compression of the ventricles
    • Obliteration of sulci
    • Localized edema = midline shift
  • Herniation 
• Lumbar puncture (LP):
  • Indicated if there are no structural abnormalities on neuroimaging
  • Done after brain imaging to avoid herniation from a rapid decrease in ICP
  • Elevated opening pressure (> 250 mm H₂O) confirms the diagnosis
  • CSF studies for infection, blood, other testing
• Labs
  • CBC 
  • Comprehensive metabolic panel (CMP)
  • Blood cultures if febrile
  • Erythrocyte sedimentation rate (ESR), CRP if concern for vasculitis

Management and Complications

Management

• Initial management:
  • Immediate support of oxygenation and blood pressure
  • Paralytic agents and adequate sedation to minimize further increases in ICP (if intubation is needed)
  • Close monitoring of vitals and ECG
  • Avoid hypotonic fluids to prevent worsening of brain edema.
• Measures to decrease ICP:
  • Elevate the head of the bed > 30º → promotes venous return
  • Hyperventilation (decrease pCO₂ to 25–30 mm Hg) → increases cerebral blood flow (CBF)
  • Mannitol: reduces intravascular volume → results in osmotic gradient → fluid moves from the extracellular to the intravascular space → brain edema is reduced
  • Hypertonic saline (bolus or continuous infusion): 
    • Tonicity of the blood increases → concentration gradient is created → fluid moves from the extracellular to the intravascular space → brain edema is reduced
    • Monitor serum Na
    • Maintain euvolemia
  • Acetazolamide = a diuretic to decrease the production of CSF
  • Induced coma (propofol): reduces sympathetic activity and metabolic demand 
  • Anticonvulsants if seizures 
  • Antipyretics if febrile (e.g., with encephalitis)
• ICP monitoring:
  • Intraventricular = gold standard
  • Intraparenchymal
  • Subarachnoid
  • Epidural
• Removal of CSF: if hydrocephalus is identified → ventriculostomy drainage
• Surgery: decompressive craniectomy
  • Normalizes ICP by opening the skull
  • Definitive treatment for masses (e.g., blood clots, tumors)

Complications

• Diffuse anoxic brain injury: due to impairment of cerebral perfusion
• Stroke: due to ischemia from decreased cerebral perfusion
• Seizures
• Coma
• Respiratory arrest: due to pressure on the brainstem
• Ophthalmologic complications: due to papilledema
• Death

Prognosis

• Highly variable: depending on the etiology and the degree of compromise
• Good prognosis with reversible causes (e.g., DKA)
• Herniation can be fatal and is the most significant cause of mortality.
• Survival after a head injury if presenting with abnormal posturing:
  •  Approximately 37% with decorticate posturing
  •  Approximately 10% with decerebrate posturing

Differential Diagnosis

• Meningitis or encephalitis: inflammation of the meninges or brain, usually due to infection. Clinically, the patient will display signs of infection, such as fever, and most will display classical signs of meningeal irritation. Cerebrospinal fluid analysis will reveal microorganisms and other cytochemical changes in bacterial cases. Diagnosis is made clinically, supported by CSF analysis. Management of bacterial meningitis includes immediate broad-spectrum antibiotics and/or antiviral medication. 
• Venous sinus thrombosis: the thrombosis of the cerebral veins and the dural sinuses, most commonly presenting with headaches and elevated ICP. Venous sinus thrombosis may also be associated with focal neurological deficits, seizures, or altered mental status. Diagnosis is made by brain MRI and magnetic resonance venography. Treatment is with anticoagulation and measures to control increased ICP.
• Intracranial mass: a tumor within the cranial vault increases the parenchymal content and increased ICP. Clinical presentation includes progressively worsening headaches and neurological deficits. Diagnosis is made with neuroimaging of the brain. Management is with steroids to decrease ICP and by treating the specific cause.
• Migraine: a primary headache disorder characterized by episodic moderate-to-severe headaches associated with photophobia, phonophobia, nausea, and/or vomiting, and might be preceded by an aura. The characteristic headache seen in migraines can be distinguished from that with increased ICP by the lack of aura and presence of papilledema. Diagnosis is made clinically and with further testing as needed. Management includes NSAIDs and triptans.
• Acute hydrocephalus: a potentially life-threatening condition caused by the excess accumulation of CSF within the ventricular system. Clinically, acute hydrocephalus can be distinguished from idiopathic intracranial hypertension by its acuity, headache severity, and cognitive deterioration. Diagnosis is confirmed with neuroimaging, which shows enlargement of the ventricles as a defining characteristic. Management is surgical with the placement of a CSF shunt.
• Stroke due to hemorrhage or ischemia: also known as a cerebrovascular accident CVA and may present with altered mental status or coma in addition to focal neurological deficits. Patients with acute strokes often present with unilateral neurologic deficits, and not present with intracranial hypertension. Diagnosis is made with physical examination and imaging. Management depends on the cause (bleed or clot), and thrombolytic therapy to restore blood flow is used with ischemic stroke.