Pancreas annulare in human embryos.

2 cases of pancreas annulare with duodenal stenosis were found among 3,307 induced abortuses of 5-12 weeks where the pancreatoduodenal area was available for examination. This corresponds to a 0.06% incidence, greatly exceeds the occurrence of the anomaly in neonates and suggests partial prenatal elimination of embryos with pancreas annulare and duodenal stenosis. Microscopic examination of serialed embryonic sections gives evidence of (1) the origin of the ring from the ventral anlage; (2) the underdevelopment of the ring material, which later may cause fibrosis of the annulus, usually observed in neonates; (3) the origin of duodenal stenosis in case of pancreas annulare till 8 weeks of fetal life; (4) the development of such stenosis not only due to atrophy of duodenal segment, resulted from compression by the pancreatic ring, but also due to anomalous differentiation of intestinal segment, the cause of which may be the disturbance of morphogenetic correlations.