We start with a quote by Rupert Willis (1 ), who said “Malformations of every conceivable kind, degree, and combination occur, and no two of them are ever alike,”to emphasize the difficulty of what we attempt to do in this chapter: provide a simplified, useful scheme for classifying neural tube defects. The difficulty results from the fact, as stated above, that individual birth defects are part of a continuum of anomalies rather than unique members of distinct classes of defects; terminology is not always logical nor is it universally accepted among embryologists, pathologists, neurosurgeons, and so forth; and the etiology of birth defects, including neural tube defects, is virtually unknown. Nevertheless, in this chapter, we provide a classification scheme, albeit an imperfect one, to help embryologists begin to understand the clinical consequences of development when it goes awry. In addition, we believe this classification scheme will be useful to clinicians for categorizing neural tube defects and will help to facilitate communication among basic scientists and clinicians as they work together in the important task of understanding neural tube defects.
