Concepts in the neurosurgical care of patients with spinal neural tube defects: An embryologic approach.

Abstract

The neural tube defects (NTDs) are a heterogeneous group of structural birth defects that arise from a complex array of multiple genetic and environmental factors and adversely affect the structure and function of the brain and spinal cord. Spinal NTDs are clinically more common than cranial NTDs. There remains a significant gap in linking the multiple NTD phenotypes to current genomic understanding. This article summarizes the neurosurgical clinical approach to spinal NTDs by correlating each step of embryonic development of the human nervous system with key management concepts for defects that arise at that step. The NTDs are broadly classified as open or closed. Open defects include myelomeningocele (MMC), encephalocele, and anencephaly. Closed defects are also known as occult spinal dysraphism and are characterized by intact skin over the spinal defect. They are more common and often cause neurologic decline from tethered cord syndrome. Failure of primary neurulation gives rise to open myelomeningocele (MMC). Surgical closure of an open MMC focuses on realigning the tissue layers that failed to separate during neurulation. In utero closure is a promising recent technique. Chronic neurosurgical management largely focuses treating hydrocephalus. The Chiari II malformation is uniformly present in MMC patients and may cause brainstem dysfunction. Tethered spinal cord may progressively impair normal neurologic function but typically responds well to surgical untethering. Surgical closure of MMC centers on approximated realignment of embryologically disordered neural tissue. Clinical surgical management decisions in the spinal NTDs remains challenging but standardized principles have emerged.