Morphologic study of embryonic development of rat duodenum through a computerized three-dimensional reconstruction: critical analysis of solid core theory.

To date, intrinsic obstructions of the duodenum have been explained by the "solid core" theory, described by Tandler in 1902 (Morphol Jahrb 29:187-216, 1902). This study aimed to evaluate the epithelial occlusion of rat duodenum during embryonic development, through optical microscopy and computerized three-dimensional reconstruction. The Wistar rat embryos used in this study had 13, 14, 15, and 16 days of gestation. This corresponds to human embryos with 33, 40, 44, and 52 days of development, which is between the fifth and eighth week. The study included 12 embryos studied by optical microscopy, and four by three-dimensional reconstruction (those with 13, 14, 15, and 16 days). Through optical microscopy, an intense epithelial proliferation was observed in the gestation embryo of 13 days, with no occlusion of the opening of the duodenum. In the embryos with 14, 15, and 16 days of gestation, an increase in diameter of the duodenum was observed along with intestinal development. Through three-dimensional reconstruction, it was observed that the opening of the digestive tube of rat embryos with 13-16 days of gestation is never obstructed by epithelial proliferation, although it may follow a sinuous path. This study concludes that the "solid core" phase described by Tandler does not occur in the embryonic development of rat duodenum.