**3. Aetiology**

Congenital duodenal obstruction occurs due to intrinsic or extrinsic mechanisms. The most common causes of intrinsic duodenal obstruction are atresia and stenosis. Intestinal embryogenesis involves rapid epithelial proliferation that results in lumen obliteration during the sixth week of gestation. This is followed by recanalization through vacuolization to re-establish the intestinal lumen in the 11th week of gestation. Failure in this step is believed to be the cause of duodenal atresia and stenosis. This is different from the principal cause of atresia in other parts of the small bowel, which is believed to result from vascular accidents [5].

Extrinsic compression of the duodenum causing obstruction occurs due to malformation of adjacent structures such as annular pancreas, preduodenal portal vein, or intestinal malrotation [6]. Annular pancreas is a condition where there is an error in the rotation and fusion of the ventral and dorsal buds of the developing pancreas during the 4–8th weeks of gestation (**Figure 1**). This often leads to the formation of a ring of pancreatic tissue encircling and obstructing the second part of the duodenum [5]. It is not totally agreed upon whether the annular pancreas actually causes duodenal obstruction from external compression or whether the malformed pancreas is just concomitant to true duodenal atresia [7]. In cases of annular pancreas with duodenal obstruction, the bile duct anatomy is often variable, with the ampulla of Vater located either above or below the level of duodenal obstruction [8–10].

*Congenital Duodenal Obstruction: Atresia, Stenosis, and Annular Pancreas DOI: http://dx.doi.org/10.5772/intechopen.111385*
