[ns] Hydrocephalus

THE NERVOUS SYSTEM

Hydrocephalus

A 3-month-old infant was admitted to the pediatrics ward because of failure to thrive and a large head. The infant stayed quietly in bed most of the day. The circumference of the head was 45 cm (normal value for this age is about 40 cm). The fontanelles protruded, and the cranial sutures were separated. The skull could be transilluminated with a flashlight. Magnetic resonance imaging showed enlarged lateral, third, and fourth ventricles. The closure of the vertebrae was defective in the lower back (spina bifida). Treatment was surgical implantation of a catheter into the lateral ventricle with drainage into the peritoneum. 1. Why are the ventricles dilated in this infant? 2. Is this a communicating or noncommunicating type of hydrocephalus? 3. What might cause this type of hydrocephalus in an infant? 4. What cerebrospinal fluid pressure would you expect in the ventricles? What is the normal level in infants? 5. In cases like this, what tends to happen to the following intracranial fluid volumes: cerebrospinal fluid, brain, and blood? 6. How can this condition affect mental function as the infant grows? What are some potential problems associated with the surgical shunt procedure? 7. Can anything similar to this happen in adults? 8. What are some of the possible complications of the associated spina bifida in this infant?

1. The ventricles in this infant are dilated because the cerebrospinal fluid (CSF) produced by the choroid plexuses in the lateral, third, and fourth ventricles cannot escape rapidly enough into the subarachnoid space through the lateral and medial foramina (of Luschka and Magendie) in the roof of the fourth ventricle. The CSF pressure therefore builds up, and this causes dilatation of the ventricles.

2. This type of hydrocephalus is noncommunicating, because the fluid communication between the ventricular system and the subarachnoid space is impaired. In communicating hydrocephalus, CSF drainage is impaired within the subarachnoid space or at the level of the arachnoid villi.

3. The obstruction in this case is likely to be caused by a malformation of the brainstem and cerebellum (Arnold-Chiari malformation), because other defects (spina bifida) in development of the nervous system are evident. Another possibility is absence or incomplete formation of the lateral and medial foramina (of Luschka and Magendie).

4. The CSF pressure that often exists in cases of infantile hydrocephalus is in the range of 200 mm H 2O. Normal CSF pressure in infants is around 40 to 90 mm H 2O. CSF pressure in adults is higher, 120 to 180 mm H2O.

5. As the ventricles in hydrocephalus dilate, they will contain more CSF; thus the CSF volume is increasing. As long as the cranial sutures are still open, the increased volume of CSF can be contained within the skull without substantially reducing the brain and blood volumes. However, as the sutures close, brain tissue and its blood supply are compromised, and nervous tissue is lost.

6. Many untreated cases of infantile hydrocephalus are fatal during the first several years. Many of the survivors are mentally retarded and have various neurologic abnormalities. Surgically treated cases result in a much greater survival rate and mental capability than untreated cases. Although surgery may yield favorable results, there are also risks. As the patient grows, shunts around the obstruction require adjustment to accommodate the larger body size; this means additional surgical procedures. The shunt may become occluded or infected. In the case of peritoneal shunts (to peritoneal cavity) the catheter can perforate one of the viscera or disrupt the function of abdominal organs.

7. Hydrocephalus can occur also in adults. However, because the cranial sutures are closed, the head does not enlarge. Instead, the ventricles expand at the expense of brain and blood volume. Hydrocephalus in adults can be produced by a number of neurologic disorders, including tumors of the brain or pituitary gland, subarachnoid hemorrhage, and meningitis. Some cases of adult hydrocephalus are associated with normal CSF pressure (hydrocephalus ex vacuo).

8. Spina bifida may be relatively harmless if it simply represents a defect in closure of the vertebrae. However, meningocele or meningomyelocele may be associated. In the latter case, there may be weakness and atrophy of the leg muscles, sensory changes in the lower extremities, and urinary incontinence. Meningitis is also a danger.