Spina bifida is a birth defect where the spine and spinal cord do not form completely during early pregnancy. This condition arises from an issue with the neural tube, the embryonic structure that develops into the brain and spinal cord. The neural tube typically closes by about 28 days after conception. When this closure is incomplete, it results in varying degrees of impact on the spinal cord and the bones of the spine. Spina bifida can range in severity, from very mild to causing significant disabilities, depending on the specific location and size of the opening, and whether the spinal cord and nerves are involved.
Spina Bifida Occulta
Spina bifida occulta is the mildest and most common form of spina bifida, often referred to as “hidden” spina bifida because it is not visible externally. It involves a small gap in one or more vertebrae, the bones of the spine, but the spinal cord and nerves usually remain unaffected within the spinal canal. Many individuals are unaware they have it, as it rarely causes symptoms.
The condition is frequently discovered incidentally during imaging tests, such as X-rays or MRI scans, performed for unrelated medical reasons. Some subtle external signs may be present on the skin directly over the defect, including a dimple, a tuft of hair, a birthmark, or discolored skin on the lower back. In a small number of cases, spina bifida occulta can lead to a “tethered cord,” where the spinal cord becomes abnormally attached to surrounding tissues, potentially causing symptoms like back pain, leg weakness, or bladder and bowel issues, especially during growth spurts.
Spina Bifida Cystica
Spina bifida cystica is a more severe form, characterized by a visible sac protruding from the baby’s back at birth. This sac contains spinal fluid and, depending on the type, may also include parts of the spinal cord or nerves. It is also known as “open spina bifida” due to the visible nature of the defect.
There are two primary types of spina bifida cystica. Meningocele involves a sac with only spinal fluid and meninges, the protective membranes surrounding the brain and spinal cord, with the spinal cord remaining in its normal position. This type can necessitate surgical correction and may lead to some disabilities.
Myelomeningocele is the most serious and common type, where the sac contains fluid, meninges, spinal cord tissue, and nerves that protrude through the spine’s opening. This damage to the nervous system often results in neurological deficits like paralysis, loss of sensation, and bladder and bowel dysfunction. Most infants with myelomeningocele also develop hydrocephalus, often requiring a shunt for drainage.
Distinguishing the Two Conditions
The primary distinction between spina bifida occulta and spina bifida cystica lies in their visibility and the degree of spinal cord involvement. Occulta is “hidden,” lacking a visible sac on the back, and the spinal cord usually remains unaffected within the spinal canal. Conversely, cystica presents with a noticeable sac protruding from the back, indicating a more extensive defect.
Occulta is often asymptomatic, with individuals rarely experiencing symptoms beyond mild back pain or localized skin changes. Cystica, especially myelomeningocele, causes neurological impairment due to exposed or damaged spinal cord and nerves, leading to muscle weakness, paralysis, and bladder/bowel control issues.
Diagnosis also varies. Occulta is often an incidental finding on imaging tests later in life. Cystica, with its visible sac, is typically diagnosed prenatally via ultrasound or immediately at birth.
Management differs significantly. Occulta usually requires no specific treatment unless complications like a tethered cord arise, which may need surgical release.
Cystica almost always requires prompt surgical repair, often shortly after birth or prenatally. Individuals with cystica need ongoing multidisciplinary care to manage complications like hydrocephalus, orthopedic issues, and bladder/bowel dysfunction.
The prognosis for occulta is generally excellent, with most individuals leading typical lives. For cystica, the prognosis involves lifelong challenges, though interventions can improve quality of life.
Causes and Prevention
The cause of spina bifida is not fully understood, but it results from a combination of genetic, environmental, and nutritional factors. A primary risk factor is folic acid deficiency during early pregnancy when the neural tube forms. Other factors increasing risk include a family history of neural tube defects, maternal diabetes, and certain anti-seizure medications during pregnancy.
Prevention focuses on adequate folic acid intake. Experts recommend all women of childbearing age consume 400 micrograms (mcg) of folic acid daily, starting at least one month before conception and continuing through the first trimester. This is important because the neural tube closes early in pregnancy, often before a woman knows she is pregnant. For women with a history of a previous child with spina bifida or a family history of neural tube defects, a higher dose of 4,000 mcg (4.0 mg) of folic acid may be prescribed. Folic acid is available through supplements and fortified foods like enriched breads, cereals, and pasta.