Spinal dysraphism is the term used for incomplete fusion of the posterior arch of the vertebrae. Closed spinal dysraphism is covered by skin and in open spinal dysraphism the spinal canal contents are exposed without overlying skin.

Open spinal dysraphism can be of two major types: (1) Myelocele with a flat neural placode (distal end of the cord) exposed and flush with the surrounding skin; (2) Myelomeningocele where the placode is associated with herniated subarachnoid space and meninges. In both the defect is repaired with approximation of the skin within the first 72 h of birth (Fig. 2.3).

Myelomeningocele is virtually always associated with Chiari II malformation. Chiari II malformation involves a small posterior fossa with downward herniation of cerebellar tonsils. In fetal life ultrasound demonstrates the bifrontal skull narrowing called lemon sign and crowding of cerebellum around the brainstem, called banana sign. In the neonate sonographic scanning of the posterior fossa and via the foramen magnum at the craniocervical junction can demonstrate the herniated cerebellar tonsils lying posterior to the upper cervical cord. Repair of the cerebellar herniation is only rarely performed in infancy [3]. The cord remains low in position after tethered cord release and closure of the myelomeningocele . It is very difficult to diagnose secondary tethering due to adhering scar tissue after surgery as the imaging findings overlap normal postoperative appearance. Clinical assessment is of utmost importance when re-tethering is suspected.

A meningocele, whether in the cervical or more commonly lumbosacral region, contains only CSF-filled sac of dura mater without any neural elements. The cord can be tethered to the periphery of the sac. It is not associated with Chiari II malformation. A terminal myelocystocele is a rare condition where the herniated CSF space communicates with the distal spinal canal. It is associated with more proximal cord syrinx. Terminal myelocystoceles are associated with omphalocele, cloacal exstrophy, imperforate anus, and spinal anomalies (OEIS) complex [7].

Closed spinal dysraphism is covered by skin. Also called as occult spinal dysraphism it is not associated with an increase in maternal serum and amniotic fluid Alpha-feto Protein (AFP) levels. Most commonly it manifests as a midline spinal abnormality on physical examination in the newborn. Bifurcation or asymmetry of the superior gluteal crease, skin covered hairy patch, skin tag, subcutaneous mass or lump (lipoma), abnormally pigmented patch, telangectasias, hemangiomas, and high sacral dimples may herald an underlying spinal dysraphic anomaly [4, 8].

Spinal lipoma is the term given to a variety of spinal dysraphisms associated with a fatty component. Lipomyelocele is akin to a myelocele, except that the neural placode is covered by a lipoma that is contiguous with the subcutaneous fat. The neural elements lie within the confines of the vertebral canal (Fig. 2.4). In a lipomyelomeningocele the subarachnoid spaces bulges out of the vertebral canal and pushes the neural placode and the overlying lipoma as well. The nomenclature of these defects can be easily understood as it represents the layer that is first encountered from the dorsal aspect [1].

Intradural lipoma is a lipoma in the subpial location that is typically attached to the dorsal spinal cord. Intradural lipomas occur more commonly in the thoracic spine, followed by the cervicothoracic junction, and may cause symptoms related to cord compression. The intradural lipomas located in the lumbosacral region, intimately related to the filum terminale, are named terminal lipomas and are often associated with tethered cord (Fig. 2.5). Terminal lipomas are frequently associated with sacral hypoplasia, anorectal malformations, genitourinary malformations, and dorsal dermal sinus.