Neural Tube Anomalies: Clinical Management by Open Fetal Surgery

Myelomeningocele (MMC), the most common congenital abnormality of the central nervous system (CNS), occurs due to failure of the neural tube to close in the first 4 weeks after conception and is characterized by a fluid-filled sac containing an exposed spinal cord and nerves. Myeloschisis is similar to MMC except that a membranous sac is not present and the defect is wider (Figure 44.1). The consequence of an open neural tube defect is abnormal development of the CNS. The neural elements become damaged from exposure to the toxic effects of amniotic fluid, leading to associated long-term morbidity and mortality. Cerebrospinal fluid (CSF) leaks out through the MMC and as a consequence the hindbrain herniates into the cervical spinal canal and blocks CSF circulation, leading to hydrocephalus and brain damage. Although 75% of individuals affected with spina bifida survive to adulthood, the one-year survival rate for infants is 88-96% [1, 2]. More than 80% of affected individuals require a ventriculo-peritoneal shunt to divert CSF in order to decompress the associated hydrocephalus, and this is dependent upon lesion level, with the need being greater for those with higher level lesions [3]. The need for a shunt is associated with complications including infection, obstruction, displacement, and shunt revisions [3, 4]. More than 75% of patients have radiographic evidence of the Chiari II malformation (hindbrain herniation, brain stem abnormalities, and a small posterior fossa) that can manifest clinically as apnea, swallowing difficulties, quadriparesis, and coordination difficulties in up to one-third of affected individuals [5-7]. Functional motor levels correlate with lesion level in approximately 39% of patients, but in over half the functional level correlates to anatomic lesions two levels higher [3]. Wheelchair use correlates with lesion level; 90% of patients with a thoracic lesion use a wheelchair while 45% with a lumbar lesion and 17% with a sacral lesion use a wheelchair [8]. Bladder and bowel incontinence are also associated with MMC, necessitating the use of bowel and bladder regimens including clean intermittent catheterization and enemas. Urologic complications include recurrent urinary tract infections, vesicoureteral reflux, and upper urinary tract dilation [9]. Additionally, the overwhelming majority of infants will require intervention for a foot deformity [10]. For those living long term with spina bifida, up to one-third of adults require daily assistance and a high rate of unexpected death has been noted [11, 12].