OPEN NEURAL TUBE DEFECTS
Meningoceles and myelomeningoceles are the most common of the congenital dysraphic states, occurring in approximately 1 per two thousand live births with the tendency to decrease in the last decade. They are a result of failure of normal midline fusion of the neural tube. Dorsal fusion defects are much more common than are their ventral counterparts.
Meningocele and myelomeningocele are characterised by an epithelium-covered sac filled with
CSF that communicates with the spinal subarachnoid space, or the sac also includes nerve roots, and spinal cord incorporated into the sac (Figs. 15-1; 15-2; 15-3).
Myeloschisis represents a severe dysraphic state in which a large placode is present at the site of the defect without meningeal encasement. This defect involves multiple levels and presents severe deficits in neurological function (Fig. 15-4).
Measuring alpha fetal protein and confirming it with amniocentesis, monitoring fetal movements, and performing imaging using ultrasonography can allow prenatal diagnosis. This allows abortion to be carried out in those women who desire to terminate their pregnancy.
Dysraphic lesions are generally affecting the normal CSF flow pattern resulting in hydrocephalus and hydromyelia. Hydrocephalus is not always evident at birth, but in about 80% of the cases may soon develop post-partum.
The aim of surgical treatment of meningoceles and myelomeningoceles is to release all structures of the nervous system inside the meningeal sac and to reposition them into the spinal canal again, to close the meningeal sac to its normal proportions and to perform plastic repair the defect of the spinal canal, the soft tissues, including the skin. These makes it possible to ensure a free flow of CSF around the neural structures, which is their natural environment and to close the spinal canal as it should be in normal conditions.
Eighty percent of open neural tube defects are found in the lubo-sacral area, 4% in the cervical area, and 16% in the thoracic area. Many children with myelomeningoceles and myeloschisis also have an associated Chiari malformation, accompanied with polymicrogyria, hydromyelia, and abnormalities of the skull base. The initial surgical problem is closing the skin defect. This is followed closely by treatment of the urological problems when the sacral nerves are involved, and of associated orthopedic problems when the extremities and the spine become deformed as a result of imbalanced motor and sensory denervations.
The preoperative studies include CT and/or and ultrasonic examination of the head to assess the ventricular size and any other malformations. A spinal X-rays helps to demonstrate the degree of kyphosis. More recently MRI studies give the greatest details of the malformations.