The brain, together with its blood vessels, the cerebrospinal fluid and spinal cord, are all contained inside the bony walls of the skull. Normally, the pressure inside the skull, known as the intracranial pressure, is regulated so it remains within certain limits. Increased intracranial pressure, when the pressure inside the skull is raised above the normal range, is potentially dangerous because the brain may be damaged, either by direct pressure on its tissues or due to the effects of raised pressure on blood vessels leading to a decreased blood supply to the brain. Possible causes of increased intracranial pressure include a brain hemorrhage, a tumor, or a rise in the amount of cerebrospinal fluid that circulates around the brain. Increased intracranial pressure is generally treated as an emergency and the patient is placed on a ventilator while fluid is drained from the skull.
Normal intracranial pressure depends on the volume of the brain remaining constant. At the same time, the cerebrospinal fluid is continually created and absorbed to maintain a steady level, and the blood flowing through the brain is regulated to remain within normal limits. When intracranial pressure begins to rise, at first more fluid is absorbed, lowering the cerebrospinal fluid pressure in an attempt to return the overall pressure inside the skull to its former level.
If the pressure continues to rise, it reaches a critical point where cerebrospinal fluid changes can no longer offset the increase. The person may have a dilated pupil and typically experiences headaches and vomiting. There may be increased blood pressure in the arteries, slowing and irregularities of the heartbeat, and breathing difficulties. As the condition progresses, part of the brain may be pushed out through the opening in the bottom of the skull, and blood flow through the brain begins to fail. These changes normally lead to brain death unless treated.
A number of conditions can give rise to increased intracranial pressure. Some do so by enlarging the brain itself, such as the swelling of brain tissue seen in diseases such as meningitis or the growth of a tumor. Other conditions increase pressure by taking up space around the brain, such as the bleeding following a head injury or hemorrhagic stroke, or a buildup of cerebrospinal fluid that may be caused by excess production or blocked drainage.
Treatment of increased intracranial pressure involves admission to the hospital and intensive care. The patient is usually placed on a ventilator to assist with breathing and given drugs to combat brain swelling, while cerebrospinal fluid is drained from the skull to lower the pressure inside. If there are treatable causes of raised pressure, such as a tumor or blood clot which can be removed, these are dealt with as soon as possible.