Spina Bifida and Chiari Malformations

Myelomeningocele is a severe form of failure of closure of the rostral neuropore. It is characterized by the posterior herniation of the spinal cord and meninges through the mesenchymal defect. It is visually evident at birth and infants experience symptoms related to the level of the involved neural structures. Common associations include Chiari malformation and hydrocephalus. Chiari malformation is an umbrella term covering various hindbrain descent abnormalities that often result in caudal brain stem and lower cranial dysfunction. Myelomeningocele as well as these two associations can cause sleep-related breathing disorders (SRBD). The mechanism of SRBD in myelomeningocele is multifactorial but relates to impaired ventilatory response to carbon dioxide and oxygen tension levels. Additionally, when Chiari malformation is present, a child can have impaired ventilatory drive from compression of the respiratory center in the brain stem and decreased tone of the pharyngeal structures related to compression of the lower cranial nerve complex. Thus, a SRBD pattern can be either central, obstructive, or a combination of both. It has been shown that patients with obstructive sleep apnea can be successfully treated by performing adenotonsillectomy and/or using continuous positive airway pressure therapy. It is less clear what the optimal treatment is for those with central sleep apnea. A combination of methylxanthines, oxygen, positive airway pressure ventilation, and posterior fossa decompression has been tried with varying degrees of success. Of note, the Chiari 1 malformation has more recently been recognized as a risk factor for SRBD. Preliminary reports suggest a higher rate of improvement in both central and obstructive apnea-hypopnea indices after posterior fossa decompression.