Congenital defect of spine and spinal cord.
Spinal Dysraphia; Myelodysplasia; Myelomeningocele; Spina Bifida Occulta.
Approximately 1:1000 live births. Risk in a subsequent sibling is 3 to 4% and up to 10% with two previously affected siblings.
Unclear. Genetic predisposition is clearly seen in the increased incidence among siblings, but nutritional and environmental factors also have a role in the pathogenesis.
Arises from the failure of the fetal neural tube to close within the first 3 weeks of gestation. This leads to the incomplete fusion of the posterior lamina and spines of the vertebral column, most commonly in the lumbosacral segments. The underlying spinal cord tissue may also have developmental abnormalities, including syringomyelia, diastematomyelia, and a tethered cord.
Clinical and radiological features. Investigation of the abnormal spine includes plain radiograph, CT scan, and MRI with or without contrast. CT scan of head is also recommended to assess the presence of hydrocephalus and other neural abnormalities. Prenatal diagnosis can be made by demonstration of the defect on ultrasonography and the detection of alpha-fetoprotein in amniotic fluid. Alpha-fetoprotein in maternal serum is an effective test for screening in high-risk patient.
Spinal dysraphias are either “open” (myelomeningoceles, myeloschisis, hemimyelomeningoceles, hemimyeloceles) or “closed” with either a lipomatous mass or not.
In “OPEN” Spinal Dysraphias: Various amounts of neural tissue and meninges herniate through the defect to form a sac-like cystic structure covered by a thin layer of skin tissue that may rupture and leak cerebrospinal fluid. Early repair and closure is recommended to reduce the risk of infection and to preserve neurological function. The extent of the neurological deficit depends greatly on the location of the meningomyelocele; it most commonly occurs in the lumbosacral region. The conus medullaris is usually disrupted and abnormal. Clinical features include flaccid paralysis of the lower limbs, absence of deep tendon reflexes, lack of response to touch and pain, and urinary and fecal incontinence. Lesions above T4 generally result in paraplegia, whereas lesions below S1 allow ambulation. Hydrocephalus in association with a Type II Arnold-Chiari Malformation occurs almost always occurs in these patients. Postural abnormalities of the lower limbs including clubfeet and subluxation of the hip are also common.
In “CLOSED” Spinal Dysraphias (Spina Bifida Occulta): There is a midline defect of the spinal column without protrusion of the spinal cord or meninges. Most affected individuals are asymptomatic and lack neurological signs. In some cases, it may be associated with patches of hair, a lipoma, discoloration of the skin, or a dermal sinus in the midline of the low back. In meningocele, the meninges herniate through the defect, but the spinal cord assumes normal ...