Intracranial hypertension (IH) is a clinical condition that is associated with an elevation of the pressures within the cranium. The pressure in the cranial vault is measured in millimeters of mercury (mm Hg) and is normally less than 20 mm Hg.

The cranium is a rigid structure that contains three main components: brain, cerebrospinal fluid, and blood. Any increase in the volume of its contents will increase the pressure within the cranial vault. The Monroe-Kellie Doctrine states that the contents of the cranium are in a state of constant volume. That is, the total volumes of the brain tissues, cerebrospinal fluid (CSF), and intracranial blood are fixed. An increase in the volume of one component will result in a decrease in volume in one or two of the other components. The clinical implication of the change in volume of the component is a decrease in cerebral blood flow or herniation of the brain.

CSF is a clear fluid found in the subarachnoid spaces and ventricles that cushions the brain and spinal cord. It is secreted by the choroid plexus in the lateral ventricles, travels to the third ventricle via the foramen of Monroe. From the third ventricle, CSF reaches the fourth ventricle through the aqueduct of Sylvius. From here, it flows into the subarachnoid space via the foramina of Magendie and Luschka and is eventually reabsorbed into the dural venous sinuses by arachnoid granulation.

The causes of increased intracranial pressure (ICP) can be divided based on the intracerebral components causing elevated pressures:

• Increase in brain volume
• Generalized swelling of the brain or cerebral edema from a variety of causes such as trauma, ischemia, hyperammonemia, uremic encephalopathy, and hyponatremia
• Mass Effect – Hematoma, Tumor, Abscess, Infarct
• Increase in Cerebrospinal Fluid – Increased production of CSF, Choroid plexus tumor
• Decreased Reabsorption of CSF – Obstructive hydrocephalus
• Increase in Blood Volume
• Idiopathic or benign intracranial hypertension
• Skull deformities such as craniosynostosis

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). TBI 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 (IIH) ranges from 0.9 to 1.0 per 100,000 in the general population, increasing in women that are overweight.

History and Physical

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, double vision from cranial nerve defects, photophobia to optic disc edema, and eventually 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 too high the elevation of blood pressure is a reflex mechanism to maintain CPP. High blood pressure causes reflex bradycardia and brain stem compromise affecting 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.