The term myelodysplasia includes a group of developmental anomalies that result from defects that occur during neural tube closure. Lesions may include spina bifida occulta, meningocele, lipomyelomeningocele, or myelomeningocele. Myelomeningocele is by far the most common defect seen and is the most devastating. This article focuses on identifying neurogenic bladder dysfunction and treatment options and describes follow-up care in children with myelodysplasia.
Spinal cord and vertebra formation begin at approximately 18 days' gestation. Closure of the spinal canal begins at the cephalad end, proceeds caudally, and is complete by 35 days' gestation. The exact cause of neurospinal dysraphism is unknown, but it appears to be multifactorial. Genetic, environmental, and nutritional factors have been implicated; however, no specific etiology has been pinpointed.
An increased frequency of neural tube defects appears to occur in the offspring of mothers who had folic acid deficiency during pregnancy. Based on these data, the current recommended daily allowance (RDA) of 400 μ g/day of folic acid was established for women during pregnancy.
Spina bifida is a broad term that may be used to describe a number of open defects of the spinal column. A meningocele occurs when the meningeal sac (the sac that envelops the spinal cord) extends beyond the confines of the vertebral canal but does not contain any neural elements. A myelomeningocele occurs when neural tissue (nerve roots, spinal cord tissue, or both) is included in the sac. A lipomyelomeningocele is defined by the presence of fatty tissue and neural elements within the sac.
Myelomeningoceles account for 90% of open spinal dysraphic states. The overwhelming majority of myelomeningoceles are directed posteriorly, with most defects involving the lumbar vertebrae. In decreasing order of frequency, sacral, thoracic, and cervical vertebrae are affected. In the rare case of an anteriorly directed defect, the sacral vertebrae are most commonly involved.
An Arnold-Chiari malformation is associated in 85% of children with a myelomeningocele. This occurs when the cerebellar tonsils herniate through the foramen magnum and obstruct the fourth ventricle, which prevents cerebrospinal fluid (CSF) from entering the subarachnoid space. These children require shunting of the ventricles, most commonly to the peritoneum. A small number (approximately 5%) of patients with myelomeningoceles do not have a neurogenic bladder, but this is the exception.
Congenital defects of spinal column formation that are not open defects are often termed spina bifida occulta. The lesions can be subtle, often with no obvious signs of motor or sensory denervation; however, in many patients, a cutaneous abnormality can be seen overlying the lower spine. This can vary from a dimple or a skin tag to a tuft of hair, a dermal vascular malformation, or an obvious subdermal lipoma.
Alterations may be found in the arrangement or configuration of the toes, along with discrepancies in lower extremity muscle size and strength, weakness, or abnormal gait. Back pain and an absence of perineal sensation are common symptoms in older children. Frequency of abnormal lower urinary tract function in patients with spina bifida occulta has been reported to be as high as 40%.
Sacral agenesis, defined as the absence of two or more lower vertebral bodies, is another defect that can produce voiding dysfunction. Because perineal sensation is usually intact and lower extremity function is normal, the only clue is often a flattened buttock and a short gluteal cleft. However, in many patients, no external signs are evident. If suspected, diagnosis is made using a lateral film of the lower spine. Even at best, only 50% of affected infants are identified in the newborn period.
The neurologic lesion produced by the dysraphism can vary widely, depending on the neural elements that have everted with the meningocele sac. The bony vertebral level correlates poorly with the neurologic lesion produced.
Additionally, different growth rates between the vertebral bodies and the elongating spinal cord can introduce a dynamic factor to the lesion. Fibrosis may surround the cord at the site of meningocele closure, and the cord can become tethered during growth. This can lead to changes in bowel, bladder, and lower extremity function. If these are noted, investigation is warranted to exclude cord tethering.
Reported prevalence of spinal dysraphism is 1 case per 1000 live births in the United States.  For unknown reasons, spinal dysraphism is more common in the eastern United States. Studies conflict regarding whether a seasonal variation occurs in prevalence. A genetic component to the disease appears to be present; if spinal dysraphism is present in one child, the chance of having a second child with the same condition is 2-5%. In addition, prevalence is increased in children born to mothers older than 30 years. Prevalence of spina bifida occulta (myelodysplasia with a closed vertebral canal) is 1 case per 4000 live births. Prevalence of sacral agenesis in children of mothers with insulin-dependent diabetes mellitus is higher than average (1%).
A large range in prevalence has been recorded internationally. Studies have demonstrated rates from 0.12-4.5 cases per 1000 live births. Prevalence of spinal dysraphism appears to be lower in Asian countries.
The meningocele sac is often nothing more than a very thin transparent tissue that may be open and leaking CSF. This is a potential source of CNS infection, which can lead to death if untreated in the perinatal period. Prompt closure of the defect is imperative. The closure itself producing neurologic symptoms is a concern, but this appears to happen in fewer than 5% of patients.
Urologic morbidity rates in patients with myelodysplasia are significant. Myelodysplasia can contribute to voiding dysfunction, urinary tract infections (UTIs), vesicoureteral reflux, and renal scarring. Surgery may be required to establish adequate bladder drainage. If not managed appropriately, myelodysplasia can cause significant urologic problems that can potentially lead to progressive renal failure, requiring dialysis or transplantation.
UTIs are common in infants with myelodysplasia, and patients must be promptly treated when recognized. Recurrent infections, especially those associated with a poorly compliant bladder and vesicoureteral reflux, can lead to pyelonephritis, renal scarring, and an eventual loss of renal function. In the absence of reflux, patients with infections are usually treated symptomatically, but in children who experience recurrent infections, prophylactic treatment can be instituted.
Vesicoureteral reflux occurs in 3-5% of infants with myelodysplasia and is usually associated with detrusor hyperreflexia or dyssynergia. If the neurogenic bladder remains untreated, incidence of vesicoureteral reflux increases with time until, by age 5 years, 30-40% of children are affected. Treatment of reflux consists of antibiotic prophylaxis to prevent infection, anticholinergic medications to lower detrusor filling pressures, and use of a method to empty the bladder, most commonly, intermittent catheterization (IC). In the most severe cases of reflux or if evidence of progressive renal scarring is apparent, surgery can be performed to lower bladder storage pressures or to provide an antireflux mechanism.
Renal damage or failure can occur as a product of repeated infections with progressive renal scarring and damage or as a result of obstruction caused by inability to empty the bladder. This can occur slowly over a period of years or with surprising rapidity, underscoring the need for regular lifelong follow-up care in patients with myelodysplasia. Even with maximal medical and surgical therapies, renal failure can occur (although rarely), and dialysis or transplantation may be needed.
Studies have not shown a significant difference between races in the prevalence of myelodysplasia. However, a study from California demonstrated a slightly higher prevalence in children born to Hispanic mothers.  White mothers were the second most likely to have children with myelodysplasia, followed by black and Asian mothers.
Myelodysplasia is more common in females than in males.
Antenatal detection of myelodysplasia can be accomplished by means of prenatal ultrasonography. If myelodysplasia is detected prenatally, cesarean delivery may improve neurologic function by reducing the trauma caused by vaginal delivery. Neural tube defects can be suspected if amniocentesis shows increased levels of alpha-fetoprotein, but these results can be misleading, with large numbers of both false-positive and false-negative results.
In many infants, myelodysplasia is detected immediately at birth; however, spina bifida occulta may not become apparent until later in life, and voiding dysfunction may be the only sign of occult disease.
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