**2.3 Classification**

Congenital duodenal obstruction as described by Gray S. and Skandalakis J. is classified into three types [33]. Type I (the most common) is usually represented by an intraluminal membrane with a normal structure of the common muscular wall for the proximal and distal segments. Duodenal stenosis belongs to this type of CDO. Type II is characterized by a short fibrous cord between the blind segments of the duodenum with separate muscle layers. Type III (rarer) is the complete separation of duodenal segments. In this anatomical variation of duodenal obstruction, multiple atresias are often present and require intraoperative exploration of the small bowel distal to the duodenal obstruction, using a liquid test.

Partial congenital duodenal obstruction or congenital duodenal stenosis, most often fenestrated membrane, is a rare cause of high intestinal obstruction in neonates. The opening in the membrane allows for passage of food and can cause duodenal obstruction of various severity. Thus, the anomaly may not be detected immediately after birth; diagnosis can be delayed even into adulthood [34]. The symptoms can mimic other conditions, such as gastroesophageal reflux disease.
