Nervous System Problems with Spina Bifida
The major initial crisis of the newborn child with spina bifida involves the nervous system — the brain, spinal cord, and peripheral nerves. The primary problem is that a portion of the nervous system is exposed and vulnerable to infection. This must be dealt with promptly to prevent infection and loss of function. Functional disturbances of the nervous system are also of concern.
How the Nervous System Works
The nervous system operates by small electrical impulses like a telephone system. Continuing the analogy, the brain acts as the computerized central telephone office. The spinal cord functions as the main cable from the central office, and the peripheral nerves of the arms, legs, bladder and bowel act as individual phone lines. Messages flow to and from the brain as electrical impulses along these lines — the nerves.
In spina bifida, problems exist at several levels in the system. The individual lines — the peripheral nerves of the legs, bladder, and bowel — are part of the deformity on the child's back. Often, they are lost during development or destroyed as the sac expands on the child's back. The closer a nerve is to the end of the spinal cord the more likely it is to be involved and lost. Unfortunately, the nerves for bladder and bowel function are connected at the very end of the spinal cord and are almost always lost.
The next nerves upward connected to the spinal cord are those for the feet, ankles, calf, knee, thigh, hip, etc., progressing up the child's trunk. Thus, as spina bifida becomes more extensive or higher on the child's back, the more likely is the loss of more and more function. However, only in rare cases is the lesion high enough to involve the arms.
Motor and Sensory Losses with Spina Bifida
There are two types of lines (peripheral nerves): outgoing and ingoing. The outgoing system is the motor nerve system and ends in the muscles of the legs, bladder, and bowel. Loss of these nerves breaks the contact with the brain, and the child loses voluntary movement of the muscles involved. In fact, if these nerves are lost early in development before birth, the affected limb is not stimulated to develop and remains smaller than normal.
The loss of motor function is not evenly distributed over the limbs and spine. The opposing muscle groups — those on the front of the leg that oppose those on the back — can be partially paralyzed and out of balance. The resulting muscle imbalance tugs and pulls the bone and limbs into various deformities. This compounds the problem of paralysis, making walking much more difficult. Orthopaedic surgeons can now correct these deformities, allowing children to stand and most to walk with assistance, although sometimes individuals with a significant amount of motor loss might find a wheelchair a better mode of transportation in adult life.
The ingoing system is the sensory system. The sensory loss is usually in the same area as the motor loss and means that the sensation of pain, temperature, and touch are lost. Without pain, which acts as the body's essential alarm system, the child has a much greater exposure to injury. One of the first ways in which parents need to be on guard against possible injury is by carefully testing the temperature of the child's bath water. Vigilance to the areas of lost sensation is key to avoiding cuts, bruises, irritation, and pressure sores.
The next level involves the covering of the main cable — the bone, muscle, and skin — which doesn’t close properly during development, remaining open like an "open book," leaving the central nervous system exposed. Parts of the cord may actually be destroyed during development, or the organization of this portion of nervous tissue may be abnormal; nerves end blindly or make wrong connections and short circuits interfere with the cord's function. Both sensory and motor pathways are involved, but usually the sensory system suffers more.
Because of both motor and sensory loss to the urinary system, a variety of abnormal patterns of function are seen. Some children retain large volumes of urine, while others can only hold a small volume of urine and dribble continuously. The sphincters that open and close to control the flow of urine and feces are deprived of voluntary control, and so require artificial aid.
Chiari II Malformation with Spina Bifida
Children born with spina bifida have a brain complication known as the Chiari II malformation. Generally speaking, all children born with spina bifida have this malformation of the brain, regardless of the presence of hydrocephalus.
There are different types of Chiari II malformations, but the kind associated with spina bifida usually is one type: the brain is compressed into the foramen magnum, the bony opening at the base of the skull through which the spinal cord exits. It is not known why this malformation is associated with spina bifida. Fortunately, the internal connections of the brain are correct, and therefore the child can still be expected to have a normal intellect.
However, in many children, subtle abnormalities of brain function are recognizable with more sophisticated forms of neuropsychological testing. The most common problem in children with spina bifida is the coordination of hand movements with what they see — hand-eye coordination. With sophisticated testing, a child's particular problem, if any, can be identified and, with proper therapy, can often be corrected or minimized.
Hydrocephalus with Spina Bifida
Another major difficulty that may be present at birth or shortly afterward is hydrocephalus; “hydro” indicates water and “cephalus” indicates the head).
The brain and spinal cord share a circulation of a salt water-like liquid called cerebrospinal fluid (CSF). The fluid is continuously made deep within the brain and flows through the brain by passing through some large compartments known as ventricles and narrower passages interconnecting the ventricles. CSF finally passes out of the brain at the back of the head and then over the surface of the brain and spinal cord to ultimately return to the blood system at the top of the brain. Any obstruction to this circulation acts much like a dam in a river.
The river below the dam decreases in size and the river above the dam expands into a lake. This extending lake of fluid fills up the ventricles within the child's brain. The increased pressure causes the child's brain and skull to expand to accommodate the enlarging amount of fluid at the center of the brain.
Fortunately, today we can control hydrocephalus. This is because of improved diagnostic equipment available to pediatric neurosurgeons that can differentiate between progressive hydrocephalus and an enlarging head that will eventually stabilize.
Because of the Chiari II deformity in children with myelomeningocele, dams or obstructions are formed along the river. In approximately 30% of the cases, the obstructions are low ones, partially obstructing the fluid, but CSF eventually spills over, and the progression becomes relentless. With early treatment, the brain impairment is reversible but left untreated the brain can be permanently damaged. Today, this is a treatable condition, and the hydrocephalus can be controlled.
Breathing Difficulties with Spina Bifida
Paralysis of the vocal cords occurs in a small percentage — approximately 2–3 percent — of children with spina bifida. It usually occurs in those children who have hydrocephalus. It is characterized by noisy breathing, also known as stridor, and is usually present at first only when the child is upset.
It may progress from airway obstruction to difficult breathing requiring an opening, known as a tracheostomy, be made at the windpipe, or trachea, below the vocal cords, thus bypassing the obstruction. Complications of hydrocephalus to this degree are rare.