Myelomeningocele is the most severe form of spina bifida, a birth defect where part of the spinal cord and its protective membranes push through an opening in the backbone and are exposed at the surface of the baby’s back. It affects roughly 1 in every 2,875 births in the United States, with about 1,278 babies born with spina bifida each year. The condition causes permanent neurological problems, but early treatment and ongoing management allow many people to live full, active lives into adulthood.
How Myelomeningocele Develops
During the first few weeks of pregnancy, the embryo forms a flat sheet of cells called the neural plate, which folds inward and closes to become the neural tube. This tube eventually becomes the brain and spinal cord. In myelomeningocele, part of this tube fails to close completely. The exact mechanisms behind this failure are still not fully understood, but both genetic and environmental factors play a role.
The result is a gap in the vertebrae (the small bones of the spine) through which the spinal cord, its surrounding membranes, and cerebrospinal fluid bulge outward into a sac visible on the baby’s back. Unlike milder forms of spina bifida where the spinal cord stays protected inside the body, in myelomeningocele the neural tissue itself is exposed or contained only within a thin membrane. This direct involvement of the spinal cord is what makes the condition so much more serious.
What It Looks Like at Birth
Newborns with myelomeningocele typically have a visible sac protruding from their back, most commonly in the lower (lumbar or sacral) region of the spine. The sac is covered by meninges, the thin membranes that normally surround the spinal cord, and contains cerebrospinal fluid and neural tissue. In some cases the sac membrane is intact; in others, the neural tissue is completely open and exposed.
The neurological effects depend heavily on where along the spine the opening occurs. Higher lesions, particularly in the thoracic (mid-back) region, tend to cause more severe problems, including complete paralysis of the legs. Lower lesions in the lumbosacral region typically cause weakness below the defect rather than full paralysis, along with reduced sensation in the legs and feet. Nearly all children with myelomeningocele have some degree of bowel and bladder dysfunction, making it one of the most common causes of neurogenic bladder in children.
Associated Brain Conditions
Myelomeningocele rarely affects the spine alone. About 69% of affected children develop hydrocephalus, a buildup of cerebrospinal fluid in the brain that increases pressure inside the skull. Without treatment, this pressure can damage brain tissue, so most of these children need a shunt (a small tube placed surgically to drain excess fluid) or a similar procedure to manage the condition.
Roughly 51% of children with myelomeningocele are diagnosed with a Chiari II malformation, a structural abnormality where the lower part of the brain extends downward into the spinal canal. This can cause problems with brainstem function, including difficulty swallowing, a weak or absent cry in infants, noisy breathing (stridor), and central sleep apnea. These symptoms require careful monitoring, especially in the first years of life.
Prenatal Diagnosis
Myelomeningocele is usually detected before birth through a combination of blood tests and imaging. A maternal blood test measuring alpha-fetoprotein (a protein produced by the developing baby) can flag potential neural tube defects. When this protein is elevated, it suggests that the baby’s skin or spinal covering isn’t fully intact, allowing the protein to leak into the mother’s bloodstream. Screening detects roughly 63% of open spina bifida cases before 24 weeks of pregnancy.
A detailed ultrasound is the main tool for confirming the diagnosis, often identifying the location and size of the defect. In some cases, an amniocentesis (testing a sample of the fluid surrounding the baby) provides additional information. Early detection is important because it opens the door to prenatal surgery, gives families time to plan, and ensures delivery happens at a hospital equipped for immediate care.
Folic Acid and Prevention
Taking folic acid before and during early pregnancy is the single most effective way to reduce the risk of myelomeningocele. Daily supplementation with 400 micrograms of folic acid, started before conception and continued through the first trimester, prevents more than 50% of neural tube defects. For women who have previously had a pregnancy affected by a neural tube defect, a higher dose has been shown to reduce the recurrence risk by 71%.
This is why folic acid is added to enriched grain products in the United States and many other countries, and why prenatal vitamins contain it as a standard ingredient. Because the neural tube closes so early in pregnancy, often before a woman knows she’s pregnant, the recommendation is for all women of childbearing age to get adequate folic acid daily.
Rates of myelomeningocele vary by ethnicity. Hispanic women have the highest prevalence at 3.80 per 10,000 live births, compared to 3.09 per 10,000 for non-Hispanic white women and 2.73 per 10,000 for non-Hispanic Black women. The reasons for these differences likely involve a combination of genetics, diet, and access to supplementation.
Surgery: Before or After Birth
Every baby with myelomeningocele needs surgery to close the opening in the spine. The critical decision is whether to perform this surgery before or after birth.
A landmark trial published in the New England Journal of Medicine compared prenatal repair (performed before 26 weeks of pregnancy) with standard postnatal repair. The results were striking: only 40% of babies who had prenatal surgery needed a shunt for hydrocephalus by age 12 months, compared to 82% of those who had surgery after birth. Prenatal surgery also improved motor function, mental development scores at 30 months, and reduced the severity of hindbrain herniation. More children in the prenatal surgery group were able to walk by 30 months.
Prenatal surgery does carry risks for the mother, including a higher chance of preterm delivery and thinning or separation of the uterine wall. The procedure requires a cesarean delivery and close monitoring for the remainder of the pregnancy. Not all pregnancies are eligible, and the surgery is only available at specialized centers. For babies who don’t receive prenatal repair, surgery is typically performed within the first day or two after birth to close the defect and protect the exposed spinal tissue from infection.
Managing Bladder and Bowel Function
Because the nerves that control the bladder and bowel originate in the lower spinal cord, most people with myelomeningocele need lifelong strategies to manage these functions. For the bladder, this commonly means clean intermittent catheterization, a technique where a thin tube is inserted into the bladder several times a day to drain urine. Many children learn to do this independently as they get older. Without consistent bladder management, urine can back up into the kidneys and cause progressive damage, making it one of the most important aspects of ongoing care.
Bowel management focuses on achieving regular, predictable bowel movements and avoiding accidents. This can involve timed bathroom routines (ideally after meals, to take advantage of the body’s natural digestive reflexes), dietary adjustments for stool consistency, and techniques such as digital stimulation or rectal irrigation. Rectal irrigation uses water introduced through a catheter to trigger the bowel’s emptying reflex and flush out the lower colon. For some individuals, a surgically created channel from the belly button to the colon allows irrigation from above, making the process easier and more independent.
Living With Myelomeningocele as an Adult
With modern medical care, the majority of people born with myelomeningocele survive into adulthood. But the condition requires ongoing attention because certain complications tend to worsen over time. Scoliosis (curvature of the spine) can progress and may eventually need surgical correction. Pressure sores become a growing concern, especially for people who use wheelchairs, because reduced sensation means skin damage can develop without being noticed. Kidney function needs regular monitoring, since years of neurogenic bladder management can gradually take a toll.
Independent mobility often decreases with age. Many children who walk with braces or assistive devices in childhood transition to wheelchair use as adults, partly due to weight gain, joint strain, and the sheer energy cost of walking with weakened muscles. This shift doesn’t necessarily mean a decline in quality of life, but it does change the practical challenges a person faces.
Women with myelomeningocele have normal menstrual cycles and can become pregnant and have healthy babies. However, pregnancy carries additional risks for them, including more frequent urinary tract infections, worsening kidney function, and a higher chance of premature labor. Because myelomeningocele has a genetic component, these women also have an elevated risk of having a child with a neural tube defect, which makes preconception folic acid supplementation especially important.