These defects occur because the caudal neural tube fails to close properly. In meningomyelocele, both the meninges and spinal cord parenchyma are included in the cystlike structure visible just above the buttocks. Because such lesions expose the CNS to the outside environment, infection is a common complication.
Myelomeningocele
Anencephaly
This is the most common and most severe of cranial neural tube defects. The orbital bones are of nearly normal size, despite absence of the brain and cranial bones, resulting in a froglike facial appearance.Anencephaly is absence of the fetal cranial vault. Exposure of cerebral tissue to amniotic fluid precludes brain development. The absence of the fetal cranial vault in anencephaly is shown here.
Anencephaly
Encephalocele
A well-developed cortical mantle characterizes this neurosurgical specimen from the occipital region of a newborn.Arnold chiari malformation
Midsagittal section showing small posterior fossa contents, downward displacement of the cerebellar vermis, and deformity of the medulla (arrowsindicate the approximate level of the foramen magnum).An Arnold-Chiari malformation occurs when there is elongation and flattening of the cerebellum and medulla with protrusion down a large conical foramen magnum.
Arnold-Chiari malformation