Oesophageal Atresia and Tracheo-Oesophageal Fistula

OA with or without a fistulous connection to the trachea is one of the more common congenital anomalies of the GI tract. It is caused by abnormal partitioning of the foregut into separate respiratory (ventral) and GI (dorsal) components early on in the first trimester of fetal life. Five different major anomalies result (Fig. 77-1). The atretic segment of the oesophagus tends to be at the junction of its proximal and middle thirds. Occasionally an isolated TOF occurs without OA; this is the H-type fistula.

Half of all children with OA and TOF have associated congenital anomalies. Features of the VACTERL spectrum (vertebral anomalies, anorectal malformation, cardiovascular malformation, tracheo-oesophageal fistula with oesophageal atresia, renal anomalies and limb defects) are especially common, with other GI malformations—notably duodenal atresia, small bowel malrotation and volvulus and a more distal congenital oesophageal stenosis often reported.¹²

OA is usually suspected on an antenatal ultrasound. The cardinal findings of maternal polyhydramnios and an absent stomach bubble have a positive predictive value of 50%.¹³ A false-negative exam may be as a result of fluid passing via a lower pouch fistula into the stomach. However, OA can be diagnosed with greater certainty by visualising the dilated, blind-ending upper oesophageal pouch and the use of cine-mode fetal MRI.^13,14

The remaining group of infants present almost immediately in the postnatal period with choking, coughing, cyanosis and drooling, symptoms which are exacerbated during attempts to feed the infant. Patients with an H-type fistula are usually symptomatic from birth.

Postnatally, the diagnosis is usually made on a chest radiograph, which shows an orogastric tube curled in the proximal oesophageal pouch (Fig. 77-2). The lungs may show features of an aspiration pneumonitis. The presence of gas in the abdomen implies a distal fistula. A gasless abdomen is seen with isolated OA or rarely OA with a proximal fistula.

In those infants in whom a primary repair is not possible, the gap between the proximal and distal oesophageal pouches can be assessed following the formation of a feeding gastrostomy. Under fluoroscopic guidance, a Hegar dilator is inserted though the gastrostomy and passed retrogradely into the distal oesophagus. A Replogle tube is simultaneously used to delineate the superior pouch. As both tubes are radiopaque, the degree of separation between the pouches is easily visualised. Thoracic CT imaging, following simultaneous injection of air into the upper pouch, via the indwelling Replogle tube, and also via the gastrostomy, can alternatively be used.^15,16

The standard, long-established diagnostic technique for an H-type fistula in most institutions remains the ‘withdrawal oesophagram’, obtained with the infant in the prone position, with a horizontal X-ray beam (or a steep oblique position with a vertical X-ray beam). The contrast is injected under pressure, via a nasogastric tube (NGT) with its tip in the distal oesophagus, as the tube is gradually pulled back under fluoroscopic guidance (Fig. 77-3). Care must be taken not to spill barium via the vocal cords into the trachea, or water-soluble contrast medium can be used. Combined bronchoscopy and oesophagoscopy should be performed if there is a high clinical index of suspicion with negative imaging.

A positive contrast medium injection to outline the proximal oesophageal pouch is rarely necessary, but occasionally required to exclude a proximal pouch fistula. Small quantities (1–2 mL) of isotonic, non-ionic contrast medium should be used under fluoroscopic guidance. A proximal fistula can also be demonstrated if air is injected into the Replogle tube during a multidetector CT (MDCT) imaging.¹⁷

Given the frequent combination of OA/TOF with VACTERL components, a preoperative work-up should involve assessment of the cardiovascular system and GU tract.

Obstruction of the Stomach

Congenital gastric obstruction is rare. It is usually due to a web or diaphragm in the antrum or pylorus. Occasionally a true atresia is present, with a fibrous cord uniting the two blind ends. Pyloric atresia is associated with epidermolysis bullosa simplex.²² The diagnosis may be suspected antenatally due to maternal polyhydramnios and a large fetal gastric bubble. Postnatally, non-bilious vomiting and upper abdominal distension are found.

A plain radiograph will show a dilated stomach with no distal air. At ultrasound, webs appear as persistent, linear, echogenic structures arising from the antral or pyloric walls and extending centrally.

Enteric Duplication Cysts

Enteric duplication cysts are uncommon congenital anomalies of obscure aetiology. They can occur anywhere along the length of the gut but are most frequently found in the ileum. Gastric duplications account for less than 5% of cases,^23,24 and are usually found on the greater curve. When located in the antropyloric region they may cause gastric outlet obstruction and present in the neonatal period with non-bilious vomiting and a palpable mass. Confirmation of the diagnosis is by ultrasound. The cysts have a layered wall, with an inner echogenic layer corresponding to the mucosa/submucosa and an outer hypoechoic layer that represents a smooth muscle layer (Fig. 77-4). This appearance is referred to as the ‘gut signature’. The contents of the cyst are usually hypoechoic, but debris is seen if there has been haemorrhage or infection has developed. Gastric mucosa takes up ^99mTc-pertechnetate, which is helpful to identify the cysts when children present with GI bleeding (see the section ‘Enteric Duplication Cysts’ under ‘Abdominal Distension’).

Gastric perforation is uncommon but accounts for a significant proportion of cases of neonatal pneumoperitoneum, and is a life-threatening condition. The underlying cause is unclear, but the rate of enteral feed introduction, ischaemia and increased mechanical pressure have been suggested.^25,26 Iatrogenic gastric perforation is recognised after insertion of orogastric tubes. A massive pneumoperitoneum is seen on a plain radiograph of the abdomen.

Small Bowel Malrotation and Volvulus

Malrotation is a generic term used to describe any variation in the normal position of the intestines. In itself, it is not necessarily symptomatic, but the resultant abnormal position of the duodenojejunal flexure (DJF) ± caecum, mean these two organs lie closer together, shortening the base of the small bowel mesentery (Fig. 77-5). The midgut has a propensity to twist around this narrowed pedicle (volvulus), compromising the arterial inflow and venous drainage of the superior mesenteric vessels, which can lead to ischaemic necrosis of the small bowel. Untreated small bowel volvulus has a high mortality rate.

In fetal life, the gut begins as a straight, midline tube, which, as it elongates and develops, herniates into the base of the umbilical cord. Traditional embryological teaching is based upon the theory that between the sixth and tenth weeks of fetal development, the midgut loop undergoes a complex three-stage anticlockwise rotation process centred around the axis of the superior mesenteric artery (SMA). This is said to explain the position of the DJF in the left upper, and the ileocaecal junction in the right lower quadrants of the abdomen. The mesentery of the small bowel extends between these two fixed points, giving it a broad base. More recent work by Metzger et al.²⁷ proposes that the anatomical position of the gut relies critically upon localised growth and lengthening of the duodenal loop, which pushes it beneath the mesenteric root.

Should the embryological development of the bowel be interrupted, then a variety of abnormal gut positions can occur; infants with congenital diaphragmatic herniae, gastroschisis and omphalocele by definition all have malrotated, malfixated bowel, although volvulus in these patients is rare after repair of the primary abnormality.²⁸ In general, small bowel malrotation is an isolated abnormality, though it has been reported in association with pyloric stenosis, duodenal stenosis, web and atresia, preduodenal portal vein, annular pancreas and jejuno-ileal atresias. The heterotaxy syndromes, Hirschsprung’s disease and megacystis–microcolon–intestinal hypoperistalsis syndrome are also associated with malrotation and volvulus, as are cloacal exstrophy, prune-belly syndrome and intestinal neuronal dysplasia.

Symptomatic babies with malrotation commonly present within the first month of life, with bilious vomiting. Older children may present with non-specific symptoms of chronic or intermittent abdominal pain, emesis, diarrhoea or failure to thrive. Volvulus, though less common in the older child, still occurs. It is important to suspect malrotation and volvulus in a child of any age with bilious vomiting, and to investigate accordingly in an emergent fashion.

There are no specific plain radiographic findings in malrotation, even with volvulus. The radiograph may be completely normal if the volvulus is intermittent or if there is incomplete duodenal obstruction, due to a loose twisting of the bowel. If the volvulus is tight, then complete duodenal obstruction results, with gaseous distension of the stomach and proximal duodenum. The classical picture is of a partial duodenal obstruction, with distension of the stomach and proximal duodenum, with some distal gas (Fig. 77-6).

On a supine radiograph, the normal DJF lies to the left of the left-sided vertebral pedicles at the height of the duodenal bulb (Fig. 77-7A). When malrotation is present, the DJF is usually displaced inferiorly and to the right side (Fig. 77-7B). It is important to remember that the DJF can be displaced temporarily by a distended colon or stomach, an enlarged spleen, an indwelling naso-enteric tube or manual palpation.

The ‘corkscrew’ pattern of the duodenum and jejunum spiralling around the mesenteric vessels is pathognomonic for midgut volvulus on the upper GI study, the calibre of the bowel decreasing distal to the point of partial obstruction (Fig. 77-8). If there is an abrupt cut-off to the flow of contrast in the third part of the duodenum, volvulus cannot be excluded with certainty and these infants too must proceed directly to surgery.

Ultrasound may demonstrate the dilated, fluid-filled stomach and proximal duodenum when obstruction is present. The relationship of the superior mesenteric vein (SMV) to the superior mesenteric artery (SMA) is abnormal in about two-thirds of patients with malrotation, when the vein lies ventral or to the left of the artery, a finding that is neither sensitive nor specific for malrotation. Ultrasound has also been proposed to confirm the (normal) retromesenteric position of the third part of the duodenum, and has been advocated as a screening tool in neonatal populations.²⁹ A volvulus may be demonstrated with ultrasound as the ‘whirlpool sign’; colour Doppler studies show the SMV spiralling clockwise around the SMA.

Management

The standard operation for small bowel malrotation and volvulus is Ladd’s procedure, whereby the bowel is exposed, untwisted and inspected. Any Ladd’s bands are divided, and the base of the mesentery is widened. Finally, the bowel is returned to the abdomen, with the duodenum and jejunum to the right side, and the colon to the left; and a prophylactic appendicectomy is often performed.

In those patients with small bowel malrotation diagnosed incidentally on an upper GI contrast study performed for another indication, management is less certain. Many paediatric surgeons will opt to perform an elective Ladd’s procedure.

It is important that radiologists understand that a Ladd’s procedure does not result in a normal anatomical position of the bowel; the DJF will always be malpositioned in these patients and recurrent volvulus can occur if the mesenteric base is not sufficiently widened at the time of the first surgery.

Duodenal Atresia and Stenosis

Duodenal atresia (DA) is much more common than duodenal stenosis, and both are caused by failure of recanalisation of the duodenal lumen after the sixth week of fetal life. Duodenal obstruction may also be caused by webs or diaphragms. Extrinsic duodenal compression by an annular pancreas or preduodenal portal vein may contribute to the obstruction in some patients. Regardless of the cause, in 80% of cases, the level of the obstruction is just distal to the ampulla of Vater.

Associated anomalies are present in the majority of patients with DA or stenosis. Down’s syndrome is present in 30% of patients and congenital heart disease in 20%. Malrotation is present in 20–30% of patients and can only be diagnosed prior to surgery if the duodenal obstruction is partial. Components of the VACTERL association may also be present, with OA coexisting in up to 10% of infants.

DA may be diagnosed antenatally when the dilated stomach and duodenal cap are seen. Fetal growth retardation, maternal polyhydramnios and consequent prematurity are common. Infants otherwise present early in the postnatal period with bilious vomiting and upper abdominal distension. Non-bilious vomiting occurs in those infants with a preampullary obstruction.

Radiographs show a gas-filled ‘double bubble’ of the stomach and duodenal cap (Fig. 77-9). If the obstruction is partial or in the rare cases of a bifid common bile duct straddling the atretic segment, then distal gas will be present.

The ‘apple peel’ syndrome is thought to follow intra­uterine occlusion of the distal SMA. There is a proximal jejunal atresia, with agenesis of the mesentery and absence of the mid-small bowel. The distal ileum spirals around its narrow vascular pedicle, an appearance which gives the syndrome its name. A malrotated microcolon is also usually present. A second, more complex type of intestinal atresia is the syndrome of multiple intestinal atresias with intraluminal calcifications.³⁰

The majority of infants with a small bowel atresia present with bilious vomiting in the immediate postnatal period. With more distal atresias, abdominal distension and failure to pass meconium are more commonly recognised clinical features.

On the plain radiograph, there are dilated loops of small bowel down to the level of the atresia. The loop of bowel immediately proximal to the atresia may be disproportionately dilated and have a bulbous contour. A meconium peritonitis with calcification of the peritoneum will be present if an intrauterine perforation has occurred.

Management is surgical, with bowel resection and primary anastomosis if possible. In infants with multiple atresias, the surgeon aims to preserve as much of the bowel length as is feasible.