Increased Intracranial Pressure

Etiology

The causes of increased ICP can be divided based on the intracerebral components causing elevated pressures, including:

• Increase in brain volume: Generalized swelling of the brain or cerebral edema from a variety of causes, eg, trauma, ischemia, hyperammonemia, uremic encephalopathy, and hyponatremia
• Mass effect
  • Hematoma
  • Tumor
  • Abscess
  • Infarct
• Increase in cerebrospinal fluid
  • Increased production of cerebrospinal fluid
  • Choroid plexus tumor
• Decreased reabsorption of cerebrospinal fluid
  • Obstructive hydrocephalus
  • Meningeal inflammation or granulomas
• Increase in blood volume
  • Increased cerebral blood flow during hypercarbia, aneurysms
  • Venous stasis from venous sinus thromboses, elevated central venous pressures, eg, heart failure
• Other causes
  • Idiopathic or benign intracranial hypertension [2]
  • Skull deformities such as craniosynostosis
  • Drugs eg, hypervitaminosis A, tetracyclines, recombinant growth hormone, lithium [3]

Epidemiology

The true incidence of intracranial hypertension is unknown. The Centers for Disease Control and Prevention (CDC) estimates that in 2010, 2.5 million people sustained a traumatic brain injury (TBI), which is associated with increased ICP. ICP monitoring is recommended for all patients with severe TBI. Studies of American-based populations have estimated that the incidence of idiopathic intracranial hypertension ranges from 0.9 to 1.0 per 100,000 in the general population, increasing in women who are overweight.[4]

Pathophysiology

The harmful effects of intracranial hypertension are primarily due to brain injury caused by cerebral ischemia. Cerebral ischemia is the result of decreased brain perfusion secondary to increased ICP. Cerebral perfusion pressure (CPP) is the pressure gradient between mean arterial pressure (MAP) and intracranial pressure (CPP = MAP - ICP).[5] When central venous pressure (CVP) exceeds ICP, the formula adjusts to CPP = MAP - CVP. The CPP target for adults following severe traumatic brain injury is recommended at >60 to 70 mm Hg, and a minimum CPP >40 mm Hg is recommended for infants, with very limited data on normal CPP targets for children in between.

Cerebral autoregulation refers to the brain's ability to maintain consistent cerebral blood flow despite fluctuations in systemic blood pressure. When MAP increases, cerebral vasoconstriction limits blood flow to preserve stable perfusion. In contrast, hypotension prompts vasodilation within the cerebral vasculature to enhance blood flow and maintain adequate CPP. This adaptive mechanism plays a critical role in protecting the brain from ischemic injury during changes in systemic circulation.

History and Physical

Clinical Features

Clinical suspicion for intracranial hypertension should be raised if a patient presents with the following signs and symptoms: headaches, vomiting, and altered mental status varying from drowsiness to coma. Visual changes can range from blurred vision and double vision resulting from cranial nerve defects to photophobia, optic disc edema, and ultimately, optic atrophy. Infants in whom the anterior fontanelle is still open may have a bulge overlying the area.

Cushing triad is a clinical syndrome consisting of hypertension, bradycardia, and irregular respiration and is a sign of impending brain herniation. This occurs when the ICP is significantly elevated, and the elevation of blood pressure is a reflex mechanism to maintain CPP. High blood pressure can cause reflex bradycardia and compromise of the brain stem, which in turn affects respiration. Ultimately, the contents of the cranium are displaced downwards due to the high ICP, causing a phenomenon known as herniation, which can be potentially fatal.[6] 

Close monitoring of neurological status plays a crucial role in the timely detection of neurological issues. Typical clinical findings include altered mental status and the emergence of a fixed, dilated pupil, both of which often indicate worsening intracranial pressure and potential impending herniation. A funduscopic exam can reveal papilledema, which is a tell-tale sign of raised ICP, as the cerebrospinal fluid is in continuity with the fluid around the optic nerve.

Evaluation

Evaluation of increased ICP requires appropriate ancillary studies in addition to a thorough medical history and a comprehensive physical examination. Early recognition of elevated ICP remains critical for preventing brain herniation and death.

Imaging Studies

Computed tomography (CT) of the head or magnetic resonance imaging (MRI) can detect signs of elevated ICP, such as ventricular enlargement, brain herniation, or mass effect resulting from tumors, abscesses, hematomas, and other space-occupying lesions. Patients with clinical findings indicative of cerebral injury should undergo a noncontrast CT scan of the brain, which may reveal cerebral edema characterized by low-density regions and loss of gray-white matter differentiation.

Additional findings may include obliteration of the basal cisterns and sulcal spaces. CT imaging can also help identify the underlying cause of increased ICP. The presence of flattened gyri, narrowed sulci, or ventricular compression further supports a diagnosis of elevated ICP. Serial CT scans provide a valuable means of monitoring the progression or resolution of cerebral edema over time.[7][8]

Lumbar Puncture

The opening pressure can be measured with a lumbar puncture. In this procedure, a needle is introduced into the subarachnoid space. This can be connected to a manometer to give the pressure of the CSF before drainage. A measurement >20 mm Hg is suggestive of raised ICP. Brain imaging should precede a lumbar puncture because a lumbar puncture can cause a sudden and rapid decrease in ICP, and the sudden change in volume can lead to herniation.

Intracranial Pressure Monitoring

Multiple devices assist in the direct monitoring of ICP.[9] A fiber optic catheter inserted into the brain parenchyma allows continuous measurement of pressure transmitted through the brain tissue. This method provides real-time data, which is crucial for clinical decision-making in critical care settings. Devices for direct ICP monitoring include: 

• External ventricular drain (EVD): A drain placed directly into the lateral ventricles can be connected to a manometer to give a reading for the pressure in the ventricles.
• Optic nerve sheath diameter (ONSD): Ultrasound measurement of the optic nerve sheath diameter has emerged as a noninvasive tool for detecting elevated ICP. Measurements are taken 3 mm behind the globe, with 2 to 3 readings obtained from each eye. A sheath diameter between 0.48 cm and 0.63 cm often indicates raised ICP.[10]
• Additional studies: Noninvasive tools, such as quantitative pupillometry and transcranial Doppler ultrasonography, may serve as useful adjuncts in assessing ICP and guiding management.[11][12]

Treatment / Management

Management Approaches

Assessment and management of the airway, along with attention to breathing and circulation, must remain the foremost priority.[13] Treatment strategies for elevated ICP should focus on 3 core principles: maintaining adequate CPP by increasing MAP, addressing the underlying cause, and reducing ICP.

Multiple interventions can help lower ICP.[14] Elevating the head of the bed above 30 degrees and keeping the neck in a neutral midline position promotes venous drainage from the brain. Hyperventilation may be used temporarily to reduce pCO2 to approximately 30 mm Hg, thereby decreasing cerebral blood flow and ICP, as hypercarbia lowers serum pH and increases cerebral blood volume.[15]

Pharmacological interventions

Osmotic agents, eg, mannitol, create an osmotic gradient that draws fluid into the vascular space, thereby reducing cerebral edema. Mannitol, typically administered at doses of 0.25 to 1 g/kg, primarily lowers ICP by decreasing blood viscosity and, to a lesser extent, blood volume. Potential adverse effects include osmotic diuresis, dehydration, and renal injury, particularly when serum osmolality exceeds 320 mOsm.[16] Hypertonic saline (commonly 3%) offers another option, given either as a 5 mL/kg bolus or continuous infusion, with serum sodium maintained below 160 mEq/dL and osmolality below 340 mOsm for safety.[17](B2)

Steroids can reduce ICP in cases of intracranial neoplasms, but should not be used in TBI. Acetazolamide, a carbonic anhydrase inhibitor, decreases CSF production and is commonly used in idiopathic intracranial hypertension. Intravenous glyburide, currently under investigation, shows promise in reducing edema after hemispheric stroke by inhibiting SUR1 receptors.[18] Barbiturates may help when sedation and conventional therapies fail to control ICP.[19](A1)

Surgical and nonpharmacological interventions

In addition to diagnostic use, lumbar puncture can relieve elevated ICP by draining CSF, though it must be avoided when mass effect is present due to the risk of herniation. EVDs serve a dual role in monitoring and removing CSF to manage ICP. Other surgical and pharmacologic options may be considered based on the severity and cause of ICP elevation. Optic nerve sheath fenestration may prevent vision loss in patients with chronic idiopathic intracranial hypertension.[20] Neurosurgical shunting, eg, ventriculoperitoneal or lumboperitoneal shunts, provides a long-term method of CSF diversion.

In refractory cases, therapeutic hypothermia (32–35 °C) can reduce ICP, although its clinical utility remains controversial. Decompressive craniectomy—removal of a skull segment and elevation of the dura—offers a last-resort surgical intervention to allow brain expansion without compression, particularly when all other measures have proven ineffective.[21]

Differential Diagnosis

Differential diagnoses that should be considered when evaluating increased intracranial pressure include:

• Blood dyscrasias and stroke
• Hydrocephalus
• Intracranial hemorrhage
• Intracranial epidural abscess
• Lyme disease
• Meningioma
• Migraine variants
• Subarachnoid hemorrhage

Prognosis

Prognosis depends on the underlying etiology and severity of the presentation. Benign intracranial hypertension does not increase the risk of death by itself; rather, the death rate is increased by morbid obesity, which is a common association with benign intracranial hypertension. Visual loss is a significant morbidity in idiopathic intracranial hypertension.

Complications

ICP can lead to a range of serious, often life-threatening complications if not promptly recognized and managed. One of the most critical outcomes is brain herniation, a condition in which brain tissue is displaced due to excessively high pressure within the rigid cranial vault. This can compress vital structures in the brainstem, resulting in loss of consciousness, impaired respiration, and ultimately death. Cushing triad—characterized by hypertension, bradycardia, and irregular respirations—is a late and ominous sign of impending herniation. Elevated ICP also compromises CPP, leading to global or focal ischemia, which can cause irreversible brain damage. Neurological deficits, ranging from cognitive impairments and motor dysfunction to vision loss from optic atrophy, may persist even after pressure normalization.

Secondary complications can arise from both the underlying cause of ICP and the interventions used to manage it. For instance, osmotic therapies, eg, mannitol, may result in electrolyte imbalances, dehydration, or renal injury if serum osmolality exceeds safe thresholds. Hypertonic saline can also cause hypernatremia if not carefully monitored. Invasive procedures, such as external ventricular drains, carry risks of infection or hemorrhage. Additionally, lumbar puncture in the presence of a mass effect can precipitate herniation by rapidly altering pressure dynamics. Long-term complications include chronic hydrocephalus, requiring permanent cerebrospinal fluid diversion through shunting, and potential neurocognitive decline, necessitating ongoing rehabilitation and support. Without proper interprofessional coordination and vigilant monitoring, the risks of long-term disability or mortality remain significant.