Fetal open spina bifida arises during early pregnancy when the neural tube, which forms the brain and spinal cord, fails to close completely. This failure results in an opening in the spine that leaves the spinal cord exposed. The severity of the condition varies, but it often has lifelong implications for an individual’s health and development.
Understanding Fetal Open Spina Bifida
Open spina bifida occurs when the neural tube fails to fuse within the first month of pregnancy, leaving a gap in the vertebrae. This opening most commonly appears in the lumbosacral (65%) or sacral (24%) regions of the back.
The most severe and common form is myelomeningocele. In this form, the spinal canal remains open, allowing the protective membranes (meninges) and the spinal cord to protrude through the opening in a sac. This exposure of the spinal cord and nerves to the surrounding amniotic fluid can cause significant damage. A rarer type is meningocele, where a sac of fluid bulges through the opening, but the spinal cord itself is not displaced, resulting in less nerve damage.
Prenatal Detection of Open Spina Bifida
The identification of open spina bifida during pregnancy often begins with a maternal serum alpha-fetoprotein (MSAFP) blood test, performed between the 15th and 20th weeks of pregnancy. AFP is a protein produced by the fetus, and abnormally high levels in the mother’s bloodstream can suggest an open neural tube defect. An elevated MSAFP result signals the need for more detailed investigation.
A high-resolution ultrasound is a primary diagnostic tool for visualizing the fetal spine and brain. Sonographers look for direct evidence of the spinal lesion and for characteristic changes in the fetal brain, known as the “lemon sign” (a scalloping of the frontal bones) and the “banana sign” (an abnormal curvature of the cerebellum). These signs are caused by the Chiari II malformation, a condition almost always associated with open spina bifida, where the brainstem is pulled lower into the spinal canal.
In some cases, an amniocentesis may be performed. This procedure involves analyzing a sample of the amniotic fluid that surrounds the fetus. Elevated levels of alpha-fetoprotein and acetylcholinesterase in this fluid are strong indicators of an open neural tube defect. For more detailed imaging, a fetal MRI may be recommended to provide a clearer picture of the spinal cord and brain.
Contributing Factors to Open Spina Bifida
The development of open spina bifida is multifactorial, resulting from a combination of genetic and environmental influences. A family history of neural tube defects suggests a genetic predisposition. Key environmental and maternal health factors include:
- Insufficient intake of folic acid (a B vitamin) before and during the very early stages of pregnancy.
- Use of certain medications during pregnancy, such as some anti-seizure drugs that interfere with folate metabolism.
- Pre-existing, poorly controlled maternal diabetes or obesity.
- Elevated maternal body temperature in early pregnancy, from a fever or use of a hot tub or sauna.
Management Strategies for Fetal Open Spina Bifida
Once a diagnosis is confirmed, parents receive extensive counseling to understand the condition and management options. It is often recommended that the baby be born at a specialized medical center with a neonatal intensive care unit (NICU) and a pediatric surgical team. A Cesarean section may be planned to avoid pressure on the exposed spinal cord during delivery.
An advancement in management is the option of fetal surgery, which involves operating on the baby in the uterus to repair the spinal lesion. The goal is to protect the exposed spinal cord from further damage caused by amniotic fluid. The Management of Myelomeningocele Study (MOMS) demonstrated that fetal surgery can reduce the need for a shunt to treat hydrocephalus (a buildup of fluid in the brain) and improve motor outcomes compared to surgery after birth.
Eligibility for fetal surgery is carefully determined based on factors like gestational age and lesion location. The procedure carries risks for both the mother and fetus, including preterm labor. For those who are not candidates or who opt against it, the standard approach is postnatal surgery, performed within the first few days of life to close the opening on the baby’s back.
Outlook and Care After Birth
For infants born with open spina bifida, care is a lifelong journey. The nerve damage that occurred in the womb is permanent and can result in a range of physical challenges, most commonly affecting the lower body. Many children with the condition experience related health issues that require ongoing management.
Common conditions associated with open spina bifida include:
- Hydrocephalus, an accumulation of excess cerebrospinal fluid in the brain, often managed with the surgical placement of a shunt.
- The Chiari II malformation, which is the displacement of brain tissue that is present in nearly all individuals with myelomeningocele.
- A tethered spinal cord, where the cord becomes attached to surrounding tissues, which can cause further neurological problems as the child grows.
- Bladder and bowel control issues, requiring management like catheterization and specialized bowel programs.
- Orthopedic concerns, such as clubfoot, hip dislocations, and scoliosis, which may necessitate braces, physical therapy, or surgery.
A multidisciplinary healthcare team, including neurosurgeons, urologists, orthopedists, and physical therapists, is involved in providing comprehensive, long-term care.