Embryologic pathogenesis of renal agenesis associated with cervical vertebral anomalies (Klippel-Feil phenotype).

Existing embryologic data suggest that the blastema of the cervical vertebrae, scapulae, and the genitourinary system have an intimate spatial relationship at the end of the 4th or beginning of the 5th week of fetal life. An alteration in this region can affect the cervical vertebrae and scapulae directly, and the genitourologic changes are mediated indirectly through the inductive capacity of the pronephric duct. The genitourinary malformation documented in patients with a specified Klippel-Feil phenotype support such an embryologic pathogenesis. Urologic pathology, in both sexes, is consistent with partial or absent induction of ureteral bud formation, and genital pathology in the female reflects partial or complete failure of müllerian duct development. These data also suggest a more frequent bilateral occurrence of these anomalies; a phenomenon that, in its most severe form, would result in bilateral renal agenesis, as illustrated by the stillborn presented in this paper.