Chapter 145. Malformations of The Spinal Cord - Review of Medical Embryology Book

Introduction: the central nervous system forms a closed tubular structure which is detached from the overlying ectoderm by the end of week 4. Malformations of the spinal cord are usually the result of problems related to the closure of the neural groove, the causes of which are still obscure. It may be the result of faulty induction by the underlying notochord, or action of environmental teratogenic factors acting on the neuroepithelial cells. Malformations involve defects in early embryogenesis since neural groove closure, in humans, usually takes place between days 21-28 of gestation

FORMATION OF THE NEURAL TUBE also affects formation of the posterior arch of the vertebra, thus, anomalies of the tube may produce anomalies of the spine as well

The most classic form of these malformations is spina bifida. The term "spina bifida" results from the fact that the posterior arch of one or more vertebrae is not formed, thus each vertebral body ends with 2 bony spines, rather than an arch, which frame the spinal cord

THE LUMBOSACRAL REGION is the most common site of spina bifida. When the spinal cord is open from top to the bottom, the condition is called rachischisis, which may be complete or partial. Failure of closure in the cephalic region is called anencephaly

THE SPINAL CORD IS OPE The nervous tissue is in direct continuity with skin, thus producing a condition similar to the general structure of the neural plate or neural groove stages of neurulation
SPINA BIFIDA refers to a wide range of defects, but is usually localized in the cord region

In its most simple form, it is seen as a failure of the dorsal portions of the vertebrae to fuse with one another (bifid spine)

Usually localized in the lumbosacral region, covered by skin and not noticeable on the surface except for the presence of a small tuft of hair over the affected are It is usually discovered by radiography
It is the most frequent type of spina bifida, affecting about 15 to 20% of the population and is referred to as spina bifida occulta
The cord (closed spinal cord) and nerves are normal, and there are usually no neurologic symptoms

If more than 1 or 2 vertebrae are involved in the defect, the meninges of the cord bulge through the opening, and a sac covered with skin is seen on the surfac This is called meningocele and surgical correction is feasible

If the sac is so large that it contains not only the meninges but also the spinal cord and its nerves, we refer to this abnormality as meningomyelocele

If there is a failure of the neural groove to close, the nervous tissue is widely exposed to the surface and we have a condition called a myelocele or rachischisis

Occasionally, the neural tissue shows much overgrowth, but the excess tissue invariably becomes necrotic before or after birth

Myelomeningoceles generally are associated with a caudal displacement of the medulla oblongata and a part of the cerebellum into the spinal canal

The myelomeningocele is frequently combined with hydrocephaly and we have what is called Arnold-Chiari malformation

DERMAL SINUS: closure of the levels above the cord is almost complete. Only a narrow opening connecting the meninges and the surface ectoderm opens to the outside. The latter may close secondarily. Lined by epidermis and skin appendages