It is a birth defect where the spinal canal and spinal tube fail to close in the womb. A baby born with meningomyelocele has a spinal cord covered by a sac. If nerves are present inside the sac, it is called meningomyelocele; if no nerves are present, it is called meningocele. If there is no sac and the spinal cord is exposed, it is referred to as myeloschisis.

Compared to meningocele, meningomyelocele and myeloschisis are more severe defects, with myeloschisis being the most severe. All three types can also affect the brain.

These problems in multiple types often cause issues with leg movements, bladder, and bowel functions.