Although spina bifida exists in forms that have no effect on function, such as spina bifida occulta, the term we use the term interchangeably with myelomeningocele.
Although the term “bifida” comes from the Latin and means “split in two,” the condition affects more than the spine. It also involves the spinal cord and its coverings; often the spinal cord and nerves are in a sac protruding from the child's back. The area involved can be anywhere along the spine but usually occurs at the bottom of the spine.
No one is sure what causes spina bifida, but the best explanation is that multiple factors are involved, some environmental and some genetic.
When a certain combination of these factors is present, normal spinal cord development is altered. Spina bifida develops during the first month of pregnancy, usually before the woman realizes she is pregnant. Neither parent is to blame.
Fetal spina bifida can be diagnosed by ultrasound examination prior to birth, between 18–22 weeks of pregnancy. This diagnosis is made in conjunction with a blood test to confirm what is found on the ultrasound. Fetal magnetic resonance imaging (MRI) may be performed to provide additional information regarding the anatomy of the spine and brain.
Occasionally, even today, a child is born with a defect so extensive that his life cannot be saved. However, most children born with spina bifida are vigorous, active newborns. But they possess a defect that, if left untreated, is potentially lethal. Early closure of the back by a neurosurgeon and control of hydrocephalus ensure survival and preserves function.
A superficial look at a child with spina bifida would suggest that the condition involves only paralysis of the legs, but brain malformations and hydrocephalus can also result. Most children with spina bifida have problems that are usually evident at birth, such as bladder and bowel dysfunction, paralysis of the legs, and lack of sensation.
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.
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.
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.
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.
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.
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.
After fetal spinal bifida is diagnosed, the staff in the Divisions of Orthopaedic Surgery and Neurosurgery at Lurie Children’s counsels the parents regarding what to expect when their baby is born. Plans are made to assure the baby is delivered in a hospital that has a neonatal intensive care unit (NICU) with a neonatologist present at the delivery. Often a cesarean delivery is necessary to avoid damaging the baby's spinal cord.
Research has yet to determine if surgery on the fetus in utero is beneficial to the infant. Researchers hypothesize that early repair may prevent hydrocephalus. However, any surgery performed in utero has additional risks. The results of these studies will determine if fetal intervention can improve the long-term outlook for children with spina bifida.
After the birth, spina bifida requires good communication between physicians and extreme vigilance on the part of families. A slight decline on a muscle test or change in bladder or bowel function may indicate a serious underlying complication such as a shunt malfunction. Shunts are tubes and valves that carry the fluid to another body cavity where it can be returned to the blood either directly or by absorption through the lining of the body cavity.
Muscle changes or changes in bladder or bowel function may also indicate a “tethered cord,” in which the spinal cord attaches to surrounding tissue and cannot move freely. Both shunt malfunctions and bladder and bowel changes need immediate intervention to prevent permanent damage.