The Embryology of Spinal Dysraphism

Abstract

The theories of abnormal embryogenesis suggested as explanations for the various forms of SBA and occult spinal dysraphism appear in some instances too all encompassing, as in Gardner's hydrodynamic theory or Padget's neuroschisis theory, or too limited, as in the theory of arrested development proposed by Daniel and Strich for the ACM, or just too speculative in many cases. The observation of a completed defect does not allow one to venture backwards in development to a specific time and cause with any accuracy. Perhaps several different causes striking different tissues at different times can set up a series of aberrations that lead to morphologically similar mature anomalies. The ability of developmental processes to heal themselves, as shown experimentally, may obscure the true mechanism and timing of occurrence although the final morphological expression may be dramatic. Since the study of human embryogenesis in the experimental laboratory is ethically unacceptable although technically feasible, the elucidation of the mechanisms of these neural defects will be long in coming.

The spinal dermal-sinus-like stalk

“…A spinal congenital dermal sinus (DS) is a developmental anomaly of the dorsal midline axis, in which a hollow, epithelium-lined tract extends inward from the skin surface for a variable distance [9]. A key feature of a DS is an open skin defect.…”

“…The outer lining of the tract is that of a white, smooth tube. The tract may end in the subcutaneous or muscular layers but predominantly continues into the intradural space, where a delicate connection with the spinal cord is frequently found [1,9,17]. In many cases, the DS is continuous with the spinal cord at this point, and finding a dissection plane between both can be difficult [17].…”

Tethered cord syndrome and occult spinal dysraphism

“…During stage 12, the caudal portion of the neural tube closes at the level L-1 or L-2. 16 Neurulation gives rise to the spinal cord only down to the lumbar spine region. The spinal cord caudal to this is formed by the process of canalization.…”

“…With the completion of neurulation, the neural tube is totally covered by cutaneous ectoderm. 16 The tail bud forms after completion of neurulation. The formation of the neural tube caudal to that formed during neurulation occurs by canalization of the tail bud, which occurs during stages 13 through 20 .…”

“…The formation of the neural tube caudal to that formed during neurulation occurs by canalization of the tail bud, which occurs during stages 13 through 20 . 16 This process consists of the development of vacuoles within the tail bud, then coalescence of these vacuoles to form the canal, which then connects with the rostral neural tube formed during neurulation. Abnormalities that develop during canalization of the tail bud can give rise to the thick terminal filum, terminal myelocystocele, and lipomyelomeningocele.…”