Neural tube defects (NTDs) are birth defects that arise during early pregnancy, often before a person knows they are pregnant. These conditions occur when the neural tube, which forms the brain and spinal cord, does not close completely. While some NTDs involve an open exposure of neural tissue, closed neural tube defects affect brain or spinal cord development in a less visible manner, as the defect is covered by skin, bone, or muscle.
Understanding Closed Neural Tube Defects
Closed neural tube defects are characterized by the neural tube failing to close completely during embryonic development, with the affected area covered by skin, bone, or muscle. This covering distinguishes them from open neural tube defects, where neural tissue is exposed. Unlike open defects, which are often immediately apparent, closed defects can be hidden, making detection more challenging.
These defects typically involve the spinal cord, with the brain rarely affected. Common examples include lipomyelomeningocele, tethered spinal cord, and sacral agenesis. Lipomyelomeningocele involves a fatty mass extending through a spinal column defect and attaching to the spinal cord, often appearing as a soft tissue swelling on the lower back.
A tethered spinal cord occurs when the spinal cord abnormally attaches to the spinal canal, limiting its movement and causing it to stretch as a child grows. This tension can damage spinal nerves and restrict blood flow. Sacral agenesis, or caudal regression syndrome, is a rare condition where part or all of the sacrum, the bone at the base of the spine, is missing. This absence can disrupt nerve supply to the lower limbs, bowel, and bladder, leading to varied functional issues.
Causes and Risk Factors
Closed neural tube defects arise from a complex interplay of genetic and environmental factors. Studies suggest a genetic component, with a higher chance of recurrence in families where a child has already been affected. Certain medications taken during pregnancy can also increase the risk.
For example, some anti-seizure drugs have been identified as contributing factors. Maternal health conditions also play a role, including uncontrolled diabetes and obesity during pregnancy. These conditions can disrupt early embryonic development.
A significant environmental factor is folic acid deficiency, a water-soluble B vitamin. Folic acid is involved in DNA synthesis and repair, processes fundamental for rapid cell division and tissue formation during neural tube development. Adequate folic acid levels are important for the neural tube to properly fold and close by the third and fourth weeks of pregnancy.
Diagnosis and Detection
Diagnosis of closed neural tube defects can occur both before and after birth. Prenatal diagnosis often involves detailed ultrasound scans, particularly the second-trimester anatomy scan, which might reveal subtle signs or structural abnormalities of the spine. Fetal Magnetic Resonance Imaging (MRI) provides detailed images of the spinal cord and surrounding structures, aiding in confirmation and understanding the defect’s extent.
Despite prenatal screening, some closed defects may not be apparent until birth or even later in childhood. Postnatal diagnosis is frequently prompted by visible skin abnormalities over the spine, which can serve as external markers of an underlying spinal issue. These signs include dimples, hairy patches, discolored skin areas, or fluid-filled cystic masses.
Neurological symptoms often emerge as a child grows, leading to further investigation. These symptoms can include weakness or numbness in the legs, difficulties with walking, or issues with bladder and bowel control. Such presentations necessitate imaging studies like ultrasound, X-rays, or MRI of the spine to identify the closed neural tube defect.
Treatment and Management
Treatment for closed neural tube defects is highly individualized, tailored to the specific type and severity of the defect. The primary goals of intervention are to manage symptoms, prevent further neurological damage, and improve overall function. Surgical repair is a common approach, particularly for conditions like tethered spinal cord.
For a tethered spinal cord, surgery aims to release the spinal cord, preventing ongoing tension and potential nerve damage. This procedure, often a laminectomy, involves freeing the spinal cord to allow it to move within the spinal canal. While surgery can relieve tension, it does not always reverse existing neurological deficits.
Beyond surgery, a multidisciplinary care team typically provides comprehensive management. Physical therapy is often initiated to improve mobility, strengthen muscles, and address gait abnormalities. Occupational therapy helps individuals develop skills for daily living and adapt to physical limitations. Urological management is also a common component of care, addressing bladder control issues and preventing urinary tract complications that can arise from nerve dysfunction.
Preventive Measures
Preventive strategies for neural tube defects, including closed types, primarily focus on adequate folic acid intake. Folic acid plays a role in the proper development and closure of the neural tube during early pregnancy. Consuming sufficient folic acid before conception and throughout the first trimester can substantially reduce the risk of these conditions.
Health organizations generally recommend that women of childbearing age consume 400 micrograms of folic acid daily. This can be achieved through fortified foods, such as cereals and breads, and dietary supplements. For individuals with a history of a neural tube defect-affected pregnancy, a higher dosage, typically 4,000 micrograms (4 milligrams) daily, is often recommended, starting at least one month before conception and continuing through the first three months of pregnancy.
Beyond folic acid, managing chronic health conditions like diabetes effectively before and during pregnancy, and avoiding exposure to harmful substances, also contribute to reducing overall risks.