1 From The Greenwood Genetic Center, Greenwood, South Carolina; Departments of Pediatrics, Reproductive Medicine, and Pathology, University of California at San Diego; Department of Pediatrics, Section of Pediatric Genetics, University of Michigan, Ann Arbor; Department of Pediatrics, University of New Mexico School of Medicine, Albuquerque; and Department of Pathology, Medical University of South Carolina, Charleston
Dissection of the abdominal vasculature in 11 cases of sirenomelia has demonstrated a pattern of vascular abnormalities that explains the defects usually found in this condition. The common feature is the presence of a single large artery, arising from high in the abdominal cavity, which assumes the function of the umbilical arteries and diverts nutrients from the caudal end of the embryo distal to the level of its origin. The steal vessel derives from the vitelline artery complex, an early embryonic vascular network that supplies the yolk sac. Arteries below the level of this steal vessel are underdeveloped and tissues dependent upon them for nutrient supply fail to develop, are malformed, or arrest in some incomplete stage. In contrast to the prevailing view that sirenomelia arises by posterior fusion of the two developing lower limbs, these studies suggest that the single lower extremity in sirenomelia arises from failure of the lower limb bud field to be cleaved into two lateral masses by an intervening allantois.
Key Words: sirenomelia vascular steal teratogenesis dysmorphology
Accepted on January 7, 1986
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