ABSTRACT
The master plan of all vertebrate embryos is based on neuroanatomy. The embryo can
be anatomically divided into discrete units called neuromeres so that each carries
unique genetic traits. Embryonic neural crest cells arising from each neuromere induce
development of nerves and concomitant arteries and support the development of specific
craniofacial tissues or developmental fields. Fields are assembled upon each other
in a programmed spatiotemporal order. Abnormalities in one field can affect the shape
and position of developing adjacent fields. Craniofacial clefts represent states of
excess or deficiency within and between specific developmental fields. The neuromeric
organization of the embryo is the common denominator for understanding normal anatomy
and pathology of the head and neck. Tessier's observational cleft classification system
can be redefined using neuroanatomic embryology. Reassessment of Tessier's empiric
observations demonstrates a more rational rearrangement of cleft zones, particularly
near the midline. Neuromeric theory is also a means to understand and define other
common craniofacial problems. Cleft palate, encephaloceles, craniosynostosis and cranial
base defects may be analyzed in the same way.
KEY WORDS
Cleft - Embryology - Tessier