- Posted August 2, 2014 by
Surgical Treatment of Hydrocephalus
Hydrocephalus, which literally means “water on the brain”, is the abnormal accumulation of cerebrospinal fluid in the brain because of blockage of its flow or absorption, or less frequently an excess of fluid production. This is a group of serious disorders for which appropriate surgical measures are clearly the treatment of choice. Modern techniques have made the treatment of hydrocephalus generally safe and effective, but this is a problem for which evaluation by a trained specialist and subsequent neurosurgical followup are necessary.
Obstructive or noncommunicating hydrocephalus is caused by blockage of the passage of cerebrospinal fluid through the ventricles of the brain and the subarachnoid space that surrounds the brain and spinal cord. This is often congenital and is primarily seen in children, but may occur in older individuals as a result of head injury, brain tumor or cerebral hemorrhage. Communicating hydrocephalus occurs when the cerebrospinal fluid can flow normally but is not properly reabsorbed by the arachnoid villi or granulations, specialized structures along the superior sagittal sinus at the top of the brain that reabsorb the fluid and return it to the venous circulation. These granulations may be absent from birth or may be scarred by meningitis, brain injury or inflammation or cerebral hemorrhage. Hydrocephalus may occur when the substance of the brain shrinks as a result of various neurological disorders and the fluid-filled ventricles increase in size, and it may occur as part of several hereditary conditions involving the brain and spinal cord.
Noncommunicating hydrocephalus can result from the blockage or failure to develop of one or more foramina, openings between the brain’s four ventricles that are named for the anatomists who discovered them (Alexander Monro, Hubert von Luschka and François Magendie). Obstruction can also occur in the aqueduct of Sylvius, a narrow channel in which cerebrospinal fluid passes through the brain stem. Such blockage is frequent in infants born with spinal bifida, in which incomplete formation of the spinal cord may be associated with fluid-filled cysts (meningocele and myelomeningocele), Fluid blockage can also be part of the Chiari malformation, in which the lower part of the brain is displaced downward and may be compressed in the foramen magnum at the base of the skull, and of the Dandy-Walker malformation, in which the cerebellum is atrophied and the flow of fluid blocked by a cyst. Hemorrhage into the ventricles of the brain may occur in premature babies, and is another cause of obstructive hydrocephalus. These kinds of hydrocephalus cause their symptoms through increased cerebrospinal fluid pressure due to the obstruction.
Communicating hydrocephalus allows the cerebrospinal fluid to flow through the ventricles and over the spinal cord, but the fluid accumulates at the site where it is to be reabsorbed, and gradually causes enlargement of the ventricles. The cerebrospinal fluid pressure is only intermittently increased, and this condition has been called normal pressure hydrocephalus for that reason. It has been suggested that the elasticity or compliance of the walls of the ventricles may decrease with time, or that the viscosity or thickness of the spinal fluid may increase, eventually resulting in symptoms. What is called hydrocephalus ex vacuo is not due to increased fluid pressure at all, but rather to a decrease in brain volume and a compensating increase in the size of the ventricles as a result of brain injury, Alzheimer’s disease and related conditions and some psychiatric disorders like schizophrenia.
Obstructive hydrocephalus in infants may be manifested by bulging of the fontanelle, the soft spot on the head that usually disappears as the skull fuses during the first year of life, and by abnormal increase in the circumference of the head. Sleepiness, irritability, vomiting, seizures and downward gaze of the eyes due to pressure on the brainstem are common symptoms. Older children may have a shrill high-pitched cry, difficulty feeding, slow development and growth and later irritability, incoordination, difficulty with memory and learning, headaches and loss of bladder control. Adults may develop headache, somnolence, nausea and vomiting, impaired coordination and abnormal eye movements and swelling of the optic nerve on eye examination. In older individuals, normal pressure hydrocephalus may develop slowly, often after a fall or a blow to the head, and can involve headache, cognitive and personality changes, a shuffling gait with difficulty picking up the feet and urinary incontinence.
The preferred treatment for hydrocephalus is surgical intervention. A shunt can be placed to bypass the site of obstruction or to drain the accumulating cerebrospinal fluid, usually from the ventricles or subarachnoid space into the peritoneal cavity in the abdomen, less frequently the right atrium of the heart, the pleural cavity in the chest, or the gallbladder. Obstructed fluid can also be drained from the lumbar spine into the peritoneum. With the development of endoscopic surgery using very small catheters, it had become possible in some cases to create a small opening when the normal one is absent or blocked, in order to allow fluid to flow normally from the site where it has accumulated. It is now possible to identify congenital causes of hydrocephalus before birth in some cases, and to correct these by prenatal surgery.
Once a shunt has been placed, it must be monitored for continued function, and may have to be replaced. Shunt malfunction can result in seizures, headaches, nausea and vomiting and hypersensitivity to light and sound. Cerebrospinal fluid may sometimes drain more rapidly with a shunt than it is produced, and these symptoms plus irritability, dizziness and vertigo, double vision and weakness of the arms or legs may occur when standing upright and disappear when lying down until the shunt can be revised. Initial evaluation and regular reassessment are needed for the management of hydrocephalus.
September has been designated Hydrocephalus Awareness Month by Congress. The Hydrocephalus Association (www.hydroassoc.org) and Pediatric Hydrocephalus Foundation (www.hydrocephaluskids.org) are sources of information about these disorders and their treatment, as is the American Association of Neurological Surgeons (www.aans.org).