6  Abdomen

Anal Atresia

Definition: Congenital absence of the opening of the anus.

Incidence: One in 5000 births.

Sex ratio: M : F = 3 : 2.

Clinical history/genetics: Sporadic, rarely familial forms with autosomal-recessive inheritance.

Embryology: Failure of division of the cloaca into the urogenital sinus and rectum, around 9 weeks after conception. Various lesions are recognized in which the rectum terminates above or below the puborectal sling. The higher the location of anal atresia, the more frequent the associated malformations. The level of atresia also determines whether primary surgical therapy is indicated after birth or whether a colostomy should be performed first, with definitive surgical correction at a later stage. This anomaly is commonly accompanied by esophageal atresia.

Teratogens: Alcohol, thalidomide, diabetes mellitus.

Associated malformations: These are found in 50%. Skeletal anomalies are associated in 30%, urogenital malformations in 38%, esophageal atresia in 10%, and cardiac anomalies in 5%.

Associated syndromes: Over 80 syndromes have been described in which anal atresia is found, including VACTERL association. Various chromosomal anomalies—e.g., partial trisomy 22q and partial monosomy 10q.

Ultrasound findings: The anus can be seen as an echogenic spot at the level of the genitals in transverse section. In the case of anal atresia, the echogenic spot is missing. Dilation of the large intestine and calcification of meconium within it may be an additional sign. These findings are first evident at a later gestational age (after 30 weeks).

Clinical management: Further sonographic screening, including fetal echocardiography. Karyotyping. Injection of contrast medium into the amniotic cavity followed by radiography of the fetus (amniofetography) have been performed in some cases historically.

Procedure after birth: Atretic anus is diagnosed at once at the first examination of the newborn after birth. Oral feeding is then contraindicated. A nasogastric tube should be inserted to relieve the secretions. In male infants, the anal fistula joins the urethra, and in the females the vagina. A blind ending of the rectum is an exception. An anus praeter is often established initially, so that definitive surgical treatment can follow at the age of 6–12 months.

Prognosis: This depends on the associated malformations. In the isolated form of anal atresia, 70% of cases show good functional capacity after surgical correction.

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Definition: Ascites is defined as a collection of fluid within the peritoneal cavity.

Clinical history/causes: Fetal hydrops, fetal cardiac insufficiency infections, mediastinal obstruction (pulmonary disease), gastrointestinal obstruction, meconium peritonitis; rarely, perforation in urinary tract obstruction, metabolic and hematological diseases of the fetus, hepatobiliary dysfunction, intra-abdominal tumors.

Ultrasound findings: The abdominal scan shows fluid accumulation as an echo-free area in the abdominal cavity. This is usually a clear diagnosis. The greater omentum may often falsely be confused with a cystic lesion in the abdomen. If only a narrow rim of ascites is found, then it is difficult to differentiate from certain artefacts.

Clinical management: Further sonographic screening, including fetal echocardiography. It is important to differentiate between isolated fetal ascites and ascites as a part of a generalized fetal hydrops. Are pleural and pericardial effusions present? Can edema of the fetal skin be demonstrated? TORCH serology (prenatal infection?), possibly amniocentesis for further clarification (infection? chromosomal anomaly? cystic fibrosis?).


Fig. 6.1 Ascites. Severe isolated fetal ascites at 25 + 6 weeks. The liver, urinary bladder and bowel loops with echoes due to meconium peritonitis are seen floating within it.

Prognosis: Frequently no cause is found for isolated fetal ascites. Spontaneous remission may occur, with a very favorable prognosis.


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Duodenal Atresia

Definition: Complete obliteration of the lumen of the duodenum.

Incidence: One in 10 000 births.

Clinical history/genetics: Mostly sporadic, rarely familial disposition.

Teratogens: Diabetes mellitus, thalidomide.

Embryology: The lumen of the intestines is obliterated with epithelium in the 5 weeks after conception: this is a physiological finding. Up until 11 weeks of gestation, recanalization occurs. Duodenal atresia is caused by failure of recanalization.

Associated malformations: These are found in 50% of cases. Skeletal anomalies, other gastrointestinal anomalies, especially annular pancreas (20%), cardiac anomalies, and renal malformations.

Associated syndromes: Over 15 syndromes with duodenal atresia have been described. Up to a third of the cases have trisomy 21.

Ultrasound findings: “Double bubble” sign: the stomach is filled with fluid and next to it, the fluid-filled proximal duodenum can be seen as a second “bubble,” with the pylorus separating the two cavities. The distal bowel is devoid of fluid. Hydramnios frequently coexists, and this is first apparent after 24 weeks.

Clinical management: Further sonographic screening, including fetal echocardiography. Karyotyping. Vaginal scan (cervical finding): premature labor? If there is hydramnios with premature contractions and maternal abdominal discomfort, drainage of the hydramnios may be necessary.

Procedure after birth: Placement of a nasogastric tube and removal of gastric secretions. The amniotic fluid appears green, due to bile reflux. Aspiration is similar to meconium aspiration. Intubation rather than mask respiration of the infant is preferred to avoid overdistension of the stomach, which facilitates aspiration. Withholding of fluid and nutrients. Early surgical correction with a duodenoduodenal or duodenojejunal anastomosis.


Fig. 6.2 Duodenal atresia. A cross-section of the fetus at the upper abdominal level at 27 weeks, showing two cystic lesions (“double bubble”) following duodenal atresia in a fetus with trisomy 21.


Fig. 6.3 Duodenal atresia. Same findings as above, in longitudinal section.

Prognosis: This depends on coexisting malformations and the maturity of the infant (premature labor due to hydramnios). Mortality can be as high as 36%. Surgical repair of isolated duodenal atresia is successful in almost all cases, with an overall survival rate of 95%.


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Intestinal Atresia and Stenosis

Definition: Congenital atresia or stenosis of the small or large bowel.

Incidence: Small-bowel atresia and stenosis occur in one in 3000–5000 births (jejunum 50%, ileum 43%, multiple stenosis 7%). Large-bowel atresia and stenosis one in 20 000.

Clinical history/genetics: Mostly sporadic. Autosomal-recessive syndromes have been described in association with intestinal atresia and stenosis. Cystic fibrosis is found in 25% of cases of jejunal and ileum atresia.

Teratogen: Thalidomide, cocaine; application of methylene blue (e.g., amniocentesis in twin pregnancy).

Embryology: Most cases are attributed to a vascular accident (hypotension, vessel anomaly, volvulus) causing local ischemia. Three types of stenosis are described:

1. Bowel continuity is disturbed by a membrane consisting of mucous and submucous parts. The tunica muscularis is not involved.

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Jan 11, 2016 | Posted by in FETAL MEDICINE | Comments Off on Abdomen
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