一、发病原因
正常肠道发育过程分3个阶段:①管腔开通阶段,在胚胎初期小肠已形成一个贯通的肠管。②上皮细胞增殖阶段,胚胎5~10周时上皮细胞增生繁殖,使肠腔闭塞,形成暂时充实期。③再度腔化阶段,胚胎11~12周时完成,闭塞肠管内出现很多空泡,彼此相互融合,使管腔再度沟通。如果胚胎肠管发育在第2或第3个月中发生障碍,某段没有出现空泡,停留于实质期,或出现空泡但未彼此融合,或融合不全,将形成肠管的闭锁或狭窄。有人认为胎儿时期肠管血循环障碍,阻碍了小肠正常发育也可产生闭锁。如脐环收缩太快、胚胎8周前胃肠管为直管状,以后肠道发育快、腹腔扩大慢,致使小肠变弯曲,腹腔容纳不下,突入脐囊内,10~12周腹腔增大,突出的中肠做逆时针方向旋转,还纳入腹腔,还纳前脐环收缩,影响该段小肠血液循环,引起萎缩,发展成狭窄或闭锁。如小肠营养血管异常,有缺损或分支畸形,或发生肠套叠均可致发育不良。
二、发病机制
1、好发部位先天性十二指肠闭锁可位于十二指肠的任何部位,但以胆总管、胰管、壶腹附近最多见,病变多在十二指肠第二段壶腹部,一般认为壶腹远端的病变较近端为多见。
2、病理类型先天性十二指肠闭锁常见有4种类型:
(1)盲管型:十二指肠近端终止于异常扩张的盲管,远端细小并与近端分离,肠管失去其连续性。
(2)索带型:十二指肠近远端均盲闭,两者之间有纤维索带相连接,此型最为罕见。
(3)盲状束袋型:十二指肠近远端虽然相连,但中间有盲状束袋形成,肠腔不通,且近端与远端直径差异甚大。
(4)隔膜型:此型最多见,占十二指肠闭锁的85%-90%。其特征为肠管保持连续性,但在第2section or the}}3There is a septum in the intestinal lumen of this section, resembling a web-like shape, which can be a single septum or multiple septa, most of which are located near the ampulla of Vater, causing varying degrees of duodenal obstruction. There is a small hole in the center or edge of the septum, with a diameter as thick as a probe, making it difficult for food to pass through. Septa without holes cause obstruction at birth, while septa with large holes may be asymptomatic or have mild symptoms. Krieg(1937) had collected cases of congenital duodenal septum21cases, among which18Cases have been statistically analyzed on the relationship between the presence and size of the septum hole and the onset time, indicating that the larger the hole in the septum, the later the symptoms appear. Some symptoms appear in childhood or adulthood. Although anatomically it is incomplete occlusion, functionally it is actually equivalent to atresia; sometimes the septum is complete, and it is also atresia anatomically, and in some cases the septum can prolapse to the3section.
3、Pathological changes in the atresia type cause complete obstruction, with the duodenum and stomach proximal to the obstruction dilated several times the normal diameter, the intestinal wall thickened, and peristalsis reduced; the duodenum distal to the obstruction is atrophied and small, in cases of complete atresia, there is no gas in the lumen, it is thinner than a chopstick, and the wall is very thin. If it is a perforated septum type, it causes incomplete obstruction, and the proximal intestinal tract is thickened, the extent of dilation is related to the degree of stenosis of the intestinal lumen and the duration of the disease.