Obstructive lesions of the small intestine from the pylorus down to the ileocecal valve may give rise to polyhydramnios in the antenatal period which is detectable by antenatal ultrasonography. As a general rule, the more proximal the lesion the more severe the degree of polyhydramnios, and distal ileal lesions may be present in the absence of polyhydramnios [5]. The list of differential diagnoses giving rise to polyhydramnios is however extensive. Another feature that may be seen on antenatal ultrasonography is the presence if dilated loops of intestine with or without echogenic bowel. While the combination of echogenic and dilated loops of bowel is often a sign of some form of intestinal abnormality, the precise nature of any problem is rarely identified before birth. One exception to this is a diagnosis of congenital duodenal obstruction in which case the appearance of a double bubble on antenatal ultrasonography has high sensitivity and specificity.

Following birth, the most common and important clinical manifestation of obstructive lesions of the GIT is bile-stained vomiting. Vomiting with truly bilious staining is always abnormal in the neonatal period and always requires investigation. Lesions in the duodenum and jejunum usually result in bilious vomiting within hours. In addition, the abdomen may appear empty or even scaphoid, and visible gastric peristalsis may be observed. Lesions lower in the ileum result in a distended abdomen if the obstruction is complete, and there may be failure to pass meconium. Obstructive lesions may also give rise to intestinal perforation in the neonatal period and occasionally antenatally. In all cases of neonatal intestinal obstruction , infants become progressively hypovolemic and are prone to circulatory and respiratory collapse. They require fluid resuscitation and may require ventilatory support. GIT obstruction should therefore be considered in any infant who is dehydrated especially if there is a history of vomiting.

Stenotic lesions of the small bowel in which the obstruction is incomplete may give rise to increased diagnostic difficulty. Affected infants may present with intermittent vomiting and episodes of partial obstruction. They eventually fail to thrive or develop complete obstruction at which stage they are fully investigated and the diagnosis becomes apparent.

Intestinal malrotation is considered separately as it may present with a spectrum of clinical scenarios depending on the degree of intestinal obstruction or midgut volvulus or both. The clinical pictures of all types of abnormal rotation are those of acute or chronic intestinal obstruction and/or acute or chronic abdominal pain suggestive of intestinal ischemia. True malrotation typically presents in the first year of life with symptoms of upper GIT obstruction including vomiting which is usually bile-stained. A coexisting volvulus may be suspected by abdominal pain , peritonitis , and hypovolemic shock associated with intestinal ischemia. However, these signs may be relatively nonspecific in the young infant. Malrotation may also present later in life.

The aim of investigating cases of suspected obstruction of the small intestine is twofold. First to identify the nature and anatomical location of the lesion to allow for planning of correct treatment and second to identify cases of malrotation in whom there is a risk of midgut volvulus and intestinal ischemia. These cases require urgent surgical intervention to reduce the risk of potentially catastrophic intestinal necrosis. The history and examination may give clues as to the location of the lesion as described above. An abdominal X-ray may simply confirm the presence of dilated intestinal loops but may also give further clues in some cases. A double bubble appearance on abdominal X-ray with a lack of air in the distal intestine (Fig. 3.2) is characteristic of duodenal obstruction. Multiple air-filled loops of proximal bowel often with air-fluid levels along with a paucity or complete absence of gas in the distal bowel is highly suggestive of obstruction of the ileum. Intestinal perforation if present will usually be apparent on abdominal X-ray, and in the rare cases of antenatal perforation, there may be widespread or localized flecks of calcification representing calcified meconium within the peritoneum.

In cases in which the diagnosis is not clear on abdominal X-ray or in which midgut malrotation or volvulus is suspected, a limited upper gastrointestinal contrast study is indicated. The classical finding in cases of malrotation is that the duodenojejunal flexure lies to the right side of the spine instead of its normal left-sided position (Fig. 3.3). This finding should prompt urgent surgical treatment due to the risk of coexisting midgut volvulus. The contrast study may also identify the presence of a stenotic segment or complete obstruction.

Cases of lower ileal stenosis or atresia are often more difficult to diagnose, and a contrast enema is invaluable in distinguishing between ileal and colonic obstruction and could be therapeutic in cases of meconium ileus (see below) .

There are four basic types of duodenal obstruction (Fig. 3.4). In type 1, there is a stenosis of the duodenum resulting from a diaphragm or web partially or totally occluding the lumen. Due to the incomplete nature of the obstruction, cases may present in childhood rather than in the neonatal period. In type 2 duodenal atresia, the proximal and distal segments end blindly but remain connected by a fibrous cord. There is complete separation of the bowel segments in type 3 and type 4 comprises an atretic segment with an annular pancreas. Multiple atresias are said to occur in up to 15 % of cases [7].

The principles of treatment are to restore intestinal continuity while avoiding interference with the ductal system draining the pancreas and biliary tree. This is best achieved using a duodenostomy in which the obstructed segment is bypassed by joining the proximal segment directly to the distal segment. Following surgery, the long-term gastrointestinal results are good [8].

Morphological classification of these lesions allows different surgeons and centers to compare outcomes, and it is also of therapeutic and prognostic value. The most commonly accepted system is that proposed by Louw [11] and modified by Grosfeld [12]. Whether the lesion is classified as ileal or jejunal is determined by the most proximal affected segment (Fig. 3.5).

Stenosis is a localized narrowing of the lumen without any break in the continuity or mesenteric defect. The intestinal wall may be thickened and rigid at the stenotic site, and there is a small, often minute lumen. The overall intestinal length is not shortened. Type I atresia is the result of a membranous web occluding the lumen with no mesenteric defect and no intestinal shortening. The lumen is usually completely occluded, and the proximal bowel therefore dilated but remaining in continuity with the collapsed distal segment. Type II atresia arises from a complete obliteration of the intestinal segment into a fibrous cord which joins two blind ends and runs in the free edge of the mesentery. There is no mesenteric defect, and once again, the total bowel length is usually normal. In both type III(a) and III(b) atresia, the intestine is likely to be shortened, and this may have significant clinical consequences. Type III(a) atresia consists of blind-ending proximal and distal bowel with no connection and an often large mesenteric defect. The blind ends are often physiologically abnormal with decreased or absent peristaltic activity which may give rise to torsion, distension, or perforation. Type III(b) atresia, also known as apple-peel atresia because of its gross morphology, may involve massive intestinal loss. It consists of intestinal atresia near the ligament of Treitz, obliteration of the superior mesenteric artery (SMA) beyond the origin of the middle colic branch, and the absence of the dorsal mesentery. The remaining intestine is coiled helically (like an apple peel) around a single perfusing vessel, often has impaired vascularity, and is almost inevitably short. Furthermore, there may be additional segments of type I or II atresia within the apple-peel segment. Such a configuration most likely arises from occlusion of the SMA due to thrombus, embolus, or strangulation as part of a midgut volvulus. In type IV atresia, there are multiple atretic segments, and the intestine may resemble a string of sausages. Overall, bowel length is usually shortened, and the intestine grossly dilated. It has been proposed that the etiology of type IV atresia may be due to failure of recanalization of solid epithelialization throughout the length of the intestine rather than from multiple single vascular events.

While it is generally accepted that stenosis and atresia of types I, II, and III(b) are the result of intrauterine vascular accidents, a genetic component has been suggested in type III(b) and IV.

The mainstay of surgical treatment for this type of lesion is resection of the atretic or stenotic segment and primary anastomosis with closure of the mesenteric defect. The proximal intestinal segment is usually dilated and functionally abnormal with absent or ineffective peristalsis. This dilated proximal segment is excised along with a short segment distal to the stenosis or atresia. It is essential to establish patency of the distal bowel by irrigation or wash out intestine, and subsequently, a primary anastomosis is performed. There is a balance to be struck between the length of dilated proximal segment resected and the risk of leaving the infant with a short length of small bowel. As such, it is almost inevitable that the caliber of proximal bowel will be greater than that of the distal intestine, and a number of techniques exist to assist construction of the anastomosis in such circumstances.

Outcome following intestinal atresia is dependent primarily on the length of remaining intestine and the presence of the ileocecal valve. Short bowel syndrome has been defined as the presence of less than 75 cm of the small intestine or 30 % of the predicted intestinal length in a premature infant [13, 14]. Outcomes following short bowel syndrome vary, and there is a high level of dependence on parenteral nutrition. However, intestinal adaptation can occur such that more than 80 % of babies with short bowel syndrome do eventually become entirely enterally nourished [15].