Brain pressure, medically known as intracranial pressure (ICP), refers to the pressure inside your skull. This pressure is exerted by the brain tissue, blood, and cerebrospinal fluid (CSF) within the rigid confines of the skull. Maintaining a stable ICP is important for proper brain function. Both abnormally high and low pressures can lead to neurological issues and require medical attention.
Understanding Brain Pressure
Intracranial pressure represents the combined pressure from the three main components inside the skull: brain tissue, blood, and cerebrospinal fluid (CSF). The Monro-Kellie doctrine explains this relationship, stating that if the volume of one component increases, another must decrease to maintain a constant total volume and stable pressure within the enclosed skull. For example, if brain tissue swells, the body attempts to compensate by reducing the volume of blood or CSF.
Normally, ICP ranges from 5 to 15 mmHg in adults when lying flat, and is lower, 0-2 mmHg, when upright. In young children, the normal range is 3 to 7 mmHg, and for infants, 1.5 to 6 mmHg. The body regulates ICP by displacing venous blood and shifting CSF into the spinal cord. CSF is continuously produced in the brain’s ventricles and reabsorbed into the bloodstream at a rate of 25 ml/hr.
Causes of Abnormal Brain Pressure
Abnormal brain pressure arises from conditions that disrupt the balance of components within the skull. High intracranial pressure (ICP), known as intracranial hypertension, results from an increase in brain tissue volume, blood volume, or CSF volume. Head injuries are a common cause, leading to conditions like epidural or subdural hematomas, which are collections of blood that press on the brain, or cerebral edema, which is brain swelling.
Strokes, brain tumors, and infections such as meningitis (inflammation of the membranes surrounding the brain and spinal cord) or encephalitis (brain inflammation) also elevate ICP. Hydrocephalus, a condition of abnormal CSF buildup within the brain’s cavities, is another cause of high ICP. Certain medical conditions, including uncontrolled high blood pressure leading to bleeding in the brain, or some medications, contribute to elevated pressure.
Conversely, low intracranial pressure (ICP), or intracranial hypotension, occurs due to a reduction in cerebrospinal fluid volume. The most frequent cause is a CSF leak, allowing the fluid to escape its normal circulation. These leaks happen after medical procedures like lumbar punctures (spinal taps) or spinal surgery, where the dura mater, the tough outer membrane covering the brain and spinal cord, is inadvertently punctured.
Traumatic injuries, like falls or sports injuries, also result in CSF leaks. In some instances, a CSF leak occurs spontaneously, without a clear precipitating event, possibly due to a pre-existing weakness in the spinal dura. Over-drainage from a shunt system, surgically placed to manage hydrocephalus, also leads to intracranial hypotension.
Recognizing the Signs
Recognizing the signs of abnormal brain pressure is important for timely medical attention. Symptoms of high intracranial pressure include a persistent, throbbing headache that worsens in the morning or with coughing or straining. Nausea and vomiting are common, and visual changes such as blurred vision, double vision, or temporary loss of vision, sometimes described as “greyed out,” occur.
Individuals also experience altered mental status, ranging from confusion and drowsiness to a decreased level of consciousness or even coma. Other signs include problems with balance and coordination, changes in behavior, or seizures. In severe cases, a combination of high blood pressure, a slow heart rate, and irregular breathing, known as Cushing’s triad, indicates a life-threatening elevation of ICP.
Low intracranial pressure manifests with a distinctive type of headache that is worse when upright and improves significantly when lying down. This positional headache increases in severity throughout the day. Other symptoms associated with low ICP include neck pain or stiffness, dizziness, and changes in hearing, such as muffled sounds or ringing in the ears (tinnitus). Blurred or double vision, facial numbness, and tingling in the arms are also present.
Diagnosis and Treatment
Diagnosing abnormal brain pressure involves a combination of clinical assessment and specific tests. A healthcare provider will perform a physical examination, including a neurological exam to assess senses, balance, and mental status. Imaging studies, such as a CT scan or MRI of the brain, are used to identify potential causes like tumors, bleeding, or swelling, and to look for signs of altered pressure. An ophthalmologic examination, specifically a funduscopic exam, reveals swelling of the optic discs, known as papilledema, which is a sign of high ICP.
In some cases, direct measurement of intracranial pressure is necessary, done through a lumbar puncture to measure cerebrospinal fluid pressure. For more continuous and precise monitoring, a catheter is surgically inserted into a brain ventricle or an intraparenchymal device is used. Identifying the exact site of a CSF leak for low ICP is challenging, sometimes requires specialized imaging like a CT myelogram.
Treatment strategies for abnormal brain pressure depend on the underlying cause and the severity of the condition. For high ICP, immediate interventions include elevating the head of the bed to promote drainage or administering medications such as mannitol or hypertonic saline, which help reduce brain swelling by drawing fluid out of the brain tissue. Diuretics like acetazolamide also decrease CSF production.
Surgical interventions are necessary to address the root cause of high ICP, such as draining excess CSF with a shunt, removing a tumor, or evacuating a hematoma. In severe, uncontrolled cases, a decompressive craniectomy, where part of the skull is temporarily removed, is performed to allow the brain to swell outward and relieve pressure. For low ICP, initial conservative measures include bed rest, increased fluid intake, and caffeine. If symptoms persist due to a CSF leak, an epidural blood patch, where a patient’s own blood is injected into the spinal canal to seal the leak, is a common procedure. Surgical repair of larger dural tears is also required.