Jonathan Markowitz, Ankur S. Narain, Fady Y. Hijji, Philip K. Louie, Daniel D. Bohl, and Kern Singh

16.1 Background

• Most congenital spinal pathologies affect the upper cervical or lumbar regions:

– Due to defective spina cord embryogenesis and/or vertebral malformation.

• Neural tube defect (NTD):

– Incomplete fusion of the neural tube during fetal development.

– Myelodysplasia is the most common type of NTD:

∘ These include spina bifida occulta, meningocele, myelomeningocele, and rachischisis.

• Spine bifida affects approximately 1,500 births annually in the United States:

– Highest rates of NTDs are found in China, Ireland, Great Britain, Pakistan, India, and Egypt.

16.2 Myelodysplasia (Spina Bifida)

• Background and etiology:

– Incomplete closure of the caudal end of the neural tube during spinal cord development and lack of fusion of vertebral arches:

∘ Development of the vertebrae and spinal column begin in the third week of embryonic development.

∘ The neural tube is created by the inward folding and fusing of the neural plate (primary neurulation).

∘ Neural tube is the embryo’s precursor to the central nervous system.

– Results in an open lesion or sac (spina bifida cystica) that can contain the spinal cord, nerve roots, and meninges:

∘ Varying degrees of myelodysplasia depending on level of failed closure.

– Environmental causes:

∘ Maternal folic acid deficiency.

∘ Maternal use of folic acid antagonists (dihydrofolate reductase inhibitors): aminopterin, methotrexate, sulfasalazine, pyrimethamine, triamterene, and trimethoprim.

∘ Antiepileptic drugs: carbamazepine, valproate, phenytoin, primidone, and phenobarbital.

∘ Maternal hyperthermia.

∘ Maternal diabetes.

– Spina bifida occulta:

∘ Mildest form.

∘ Unfused vertebral arch.

∘ Meninges do not herniate through the opening in the spinal canal.

– Meningocele:

∘ A subset of spina bifida cystica:

▪ Spinal elements are contained within a sac.

∘ Herniation of the meninges (excluding the spinal cord), through the opening in the spinal canal.

– Myelomeningocele:

∘ A subset of spina bifida cystica.

∘ Herniation of the meninges and the spinal cord through the opening in the spinal canal.

– Rachischisis:

∘ Neural elements exposed with no covering.

• Presentation:

– Mild forms (i.e., spina bifida occulta) may be asymptomatic:

∘ Occasional abnormal tuft of hair or small dimple at the site of the spinal malformation.

– Meningocele or myelomeningocele will present with a cyst containing neural elements.

– Neurological symptoms can include bladder, motor, and sensory paralysis below the level of the spinal lesion.

– Often associated with latex allergy.

∘ Lesion of L3 or above are mostly confined to a wheelchair.

– Changes in functional level should alert the physician to the possibility of tethered cord syndrome:

∘ Formation of fibrous attachments between the spinal cord and spinal canal:

▪ Results in stretching of the spinal cord and progressive cord damage and neurologic deficit.

• Clinical evaluation:

– Examination should include assessment of level and degree of motor and sensory function, range of motion (ROM), spinal deformity, integrity of the skin, and associated deformities and contractures.

– Prenatal laboratory diagnosis:

∘ Maternal screening of serum alpha fetoprotein (AFP) levels:

▪ Performed ideally at 16 to 18 weeks of gestation, but can be performed as early as 15 weeks or as late as 20 weeks.

▪ First trimester screening is not recommended because of low sensitivity.