The bones of the spine do not completely form, and the spinal canal is incomplete. Spina bifida includes any congenital defect involving insufficient closure of the spine. The cause of myelomeningocele is unknown. However, folic acid deficiency is thought to play a part in neural tube defects such as myelomeningocele. A viral cause or trigger has been theorized because there is a higher incidence of the defect in children born in the early winter months.
Research also indicates possible environmental factors such as radiation.
Protrusion of the spinal cord and meninges damages the spinal cord and nerve roots, causing a decrease or lack of function of body areas controlled at or below the defect. Symptoms are related to the anatomic level of the defect. Symptoms include partial or complete paralysis of the legs, with corresponding partial or complete lack of sensation , and may include loss of bladder or bowel control . Prospective mothers may be screened to determine their serum folate level . Neurologic examination may indicate loss of neurologic functions below the defect.