Esophageal atresia (EA) encompasses a group of congenital anomalies comprising an interruption of the continuity of the esophagus with or without a persistent communication with the trachea. In most cases there is a tracheoesophageal fistula (TEF); in 7% there is no fistulous connection, while in 4% there is a TEF without atresia. EA with or without TEF accounts is seen in about 1:3000 to 1:4000 live births. It is 2 to 3 times more frequent among twins, and males are affected slightly more than females.
Esophageal atresia is classified into 5 types on the basis of the anatomy and site of the TEF (Gross classification) (Figure 17-37).16
Type A. This represents the isolated form of esophageal atresia without TEF and accounts for 7% to 8% of cases. The esophagus is divided in a proximal segment, which is dilated, thick walled, and reaches the posterior mediastinum at the second thoracic vertebra, and a distal segment, which is short and ends above the diaphragm.
Type B. This variant is described as the combination of esophageal atresia with proximal TEF and occurs in 2% of cases. The fistula is located on the anterior wall of the esophagus and 1 to 2 cm above the end.
Type C. This is the most common variant (86%) and consists of a dilated esophagus with a thickened muscular wall, which ends blindly in the superior mediastinum at the level of the third and fourth thoracic vertebra. The distal esophagus is thinner and narrower and enters the posterior wall of the trachea at the carina or more proximally. The distance between the proximal portion of the esophagus and the distal fistula varies from overlapping segments to a wide gap.
Type D. This is defined as esophageal atresia with proximal and distal TEF. It is the less frequent form, occurring in less than 1% of cases.
Type E. This is the TEF without esophageal atresia and represents 4% of cases. This form is characterized by an anatomically normal esophagus, which is connected with the trachea through a fistula commonly located in the lower cervical region. The fistula may be very narrow or 3 to 5 mm in diameter, and is usually single, although multiple fistulas have been occasionally reported.
Five types of esophageal atresia with and without tracheoesophageal fistula.
The mechanism that leads to esophageal atresia/TEF is still unknown, although animal studies have allowed detailed analysis of failed organogenesis underlying the condition. The most accredited theory postulates that the primary defect consists of the incomplete separation of the foregut into the ventral respiratory portion and the distal digestive portion at 8 weeks' gestation, because of either failure of tracheal growth or failure of the normally developed trachea to separate from the esophagus.17 Alternatively, it has been proposed that the primary insult is the atresia of the proximal esophagus followed by the establishment of a connection between the trachea and esophagus (TEF).18
Ancillary Ultrasound Signs
The anatomical visualization of the esophagus by echogenic lines, which represents the apposition of the collapsed anterior and posterior esophageal walls (see Figure 17-5A and B), might in and of itself not be sufficient to aid in the diagnosis of esophageal anomalies.
The sonographic diagnosis of esophageal atresia/TEF is based on the detection of both polyhydramnios and a small or absent fetal stomach bubble (Figure 17-38). Absent or a subjectively small stomach bubble must be followed up, because of its association with esophageal atresia. Other sonographic signs are polyhydramnios combined with fetal growth restriction, a C loop indicating the association with duodenal atresia or stenosis, and the detection of a proximal esophageal pouch.
Axial view of the fetal abdomen at 28 weeks, showing no gastric bubble (arrow). There is also polyhydramnios.
Because esophageal atresia/TEF is commonly associated with an upper pouch, the presence of polyhydramnios and absent fetal stomach should prompt the evaluation of the upper esophageal segment in order to identify the "pouch sign" in the neck or mediastinum. This sonographic marker appears as an anechoic mass (Figure 17-39) and can be observed in the early third trimester, although its detection as early as 23 weeks' gestation has been reported.19 Because of paucity of reports described in the literature, the sensitivity and accuracy of the pouch sign in identifying fetuses with esophageal atresia/TEF is still undetected. The differential diagnosis of the pouch sign includes lymphovascular malformations and cervical cyst teratoma.
Sagittal view of the neck and thorax in a third trimester fetus showing a "pouch sign" (arrow) due to the esophageal atresia. Color Doppler depicts heart (H) and neck vessels.
Another additional and inconstant sign is fetal growth restriction. Because polyhydramnios is usually associated with fetal macrosomia, the presence of increased amniotic fluid and restricted growth should raise the suspicion of esophageal atresia/TEF. Fetal growth restriction affects 40% of fetuses with esophageal atresia/TEF, probably as a result of reduced intestinal absorption mainly in late gestation.
The combination of duodenal and esophageal atresia is characterized by a C-shaped fluid collection in the fetal abdomen (Figure 17-40), which results from a closed-loop bowel obstruction involving the distal esophagus, stomach, and duodenum.
Axial view of a 22-week fetus showing a marked distension of the stomach and duodenum, which form a "C loop" (arrows). This finding is typical of duodenal atresia combined with an esophageal atresia.
The prenatal diagnosis of esophageal atresia/TEF is limited by several factors. Although the presence of polyhydramnios, small or absent stomach, and pouch sign is highly suggestive for esophageal atresia/TEF, a wide range of pathologic conditions is associated with increased amniotic fluid and nonvisualization of the gastric bubble. Furthermore, the definition of a "small" gastric bubble is subjective and fairly reproducible.19 In addition, the presence of an upper pouch and distal fistula allows the amniotic fluid to flow and fill the stomach. The amount of fluid able to cross the fistula channel is not enough to prevent the onset of polyhydramnios, but is responsible for the detection of a constantly small gastric bubble, which makes the ultrasonographic diagnosis of esophageal atresia/TEF virtually impossible. Finally, the pouch sign is a transient finding that can be detected only when the fetus swallows.
The differential diagnosis includes a number of conditions associated with polyhydramnios and reduced size of the fetal stomach. Obstruction of the fetal GIT proximal to the ileum, facial cleft, and central nervous system disorders leading to depression of swallowing are common causes of polyhydramnios. A nonvisible stomach is present in up to 1% of normal fetuses on initial scans, for which strict follow-up is mandatory. The C-loop sign should be differentiated from other intraabdominal cysts.
Associated anomalies can be found in 50% to 70% of infants with esophageal atresia/TEF.20 Esophageal atresia/ TEF is part of a phenotype of associations and syndromes, such as VACTERL (vertebral, anorectal, tracheoesophageal, renal, and limb anomalies), CHARGE (coloboma, heart defects, atresia choanal, retarde growth, genital hypoplasia, and ear deformities), Potter syndrome (renal agenesia, pulmonary hypoplasia, typical dysmorfic facies), and Schiss association (omphalocele, cleft lip/palate, genital hypoplasia). Trisomy 21 and 18, and 13q deletion may also present esophageal atresia/TEF in their spectrum of features. Fetuses with Down syndrome are more likely to present isolated esophageal atresia in as many as 50% of cases. The most frequent cardiac anomalies are ventricular septal defects and tetralogy of Fallot. The vertebral anomalies regard mainly the thoracic region and lead to scoliosis in later stages. Other structural defects associated with esophageal atresia/TEF include duodenal atresia, malrotation, pyloric stenosis, cleft lip/palate, omphalocele, Meckel diverticulum, annular pancreas, lung abnormalities, choanal atresia, and hypospadia. However, 78% of these anomalies may be undetected prenatally.20
The majority of cases of esophageal atresia are sporadic and nonsyndromic, and familial cases account for less than 1%. There is no known pattern of inheritance and the recurrent risk in a sibling of an affected child is approximately 1%.
Because 20% to 44% of fetuses with esophageal atresia/TEF present chromosomal anomalies, mainly trisomy 21 and 18, fetal karyotype is recommended. The risk of carrying trisomy 21 is particularly enhanced if esophageal atresia is associated with duodenal atresia.
The peristalsis of the esophagus is always compromised in infants affected with esophageal atresia/TEF due to abnormal neuropeptide distribution or vagal nerve damage occurring during surgical repair. The trachea is also anomalous because of an absolute deficiency of the tracheal cartilage and an increased length of the transverse muscle in the posterior wall. In the severe forms, tracheomalacia with tracheal collapse may develop in proximity of the fistula. Therefore, delivery should take place in a tertiary referral center, which can provide neonatal intensive care and pediatric surgery.
When lethal congenital anomalies are not present, the survival rate is more than 95%. At birth, a suction catheter, located in the upper esophageal pouch, is necessary to remove secretions and prevent aspiration. Furthermore, the increased pulmonary resistance induces respiratory gases moving down through the distal fistula into the stomach, leading to distension and rupture of the stomach. Particular attention is warranted in preterm infants, who are likely to need endotracheal intubation and mechanical ventilation.
Postnatal surgery consists of dividing the fistula distal to its entry in the trachea and closing the defect with interrupted sutures. Successively, the proximal blind end of the esophagus is linked to the lower esophageal segment. On the second or third day after surgery, feeding via the transanastomotic tube may be allowed, and oral feeding is gradually introduced. Stenosis at the site of anastomosis can be observed in one-third of the infants, and in most cases it resolves after dilatation.16 In later infancy, substitution of the esophagus with stomach or bowel can be attempted. Long-term complications include food bolus obstruction (16%), tracheomalacia (10%), and gastroesophageal reflux with recurrent respiratory infections, and vomiting and poor growth (40%).16 The quality of life for adults after at least 20 years from surgical repair of esophageal atresia/TEF is comparable to the normal population.21
Emerging Concepts and Future Directions
Direct visualization of the fetal esophagus is feasible with very high frequency transducers in approximately 87% of midtrimester fetuses, and esophageal motility can be followed from pharynx to stomach in 30% of cases.21 However, the efficacy of the anatomical assessment of the esophagus in identifying fetuses with esophageal atresia/TEF is still undetected, and further investigations are required before incorporating this examination in sonographic surveys of fetal anatomy.
Magnetic resonance (MR) has revealed a useful tool to assess fetal thoracic lesions. The sensitivity of MR in diagnosing esophageal atresia/TEF is not well established because of different criteria in selecting fetuses, which may benefit of further studies. Langer et al reported a 100% sensitivity of MR for the identification of 5 fetuses with esophageal atresia/TEF,22 whereas in the series presented by Levine et al, nonvisualization of the esophagus in MR scans occurred in 64% of examinations.23 Such a discrepancy may be explained by the different indications for performing MR, being ultrasound findings of polyhydramnios and absent stomach bubble in the series by Langer et al, and suspicion of chest lesions in the series by Levine et al. Further studies are needed to investigate the efficacy of MR as a complement to the sonographic evaluation.
Esophageal atresia is commonly associated with TEF.
A nonvisualized stomach bubble or subjectively small stomach bubble must be followed up and may indicate esophageal atresia.
The detection of polyhydramnios and absent/small fetal stomach is highly suggestive of esophageal atresia/TEF, as well as the association between polyhydramnios and fetal growth restriction.
Sonographic markers that should arouse the suspicion of esophageal atresia/TEF are the "pouch sign" in the mediastinum and the C-loop in the abdomen.
Because 50% to 70% of fetuses with esophageal atresia/ TEF present associated structural defects, a detailed survey of fetal anatomy is mandatory when esophageal atresia/ TEF is suspected.
Fetal karyotype is highly recommended.
Duodenal atresia is the absence or abnormal narrowing of the segment between the proximal and distal portions of the duodenum. It occurs in 1:5000 pregnancies and 0.6:10,000 live births.24 In 80% of cases, the obstruction of the lumen is located caudally to the Vater ampulla and is complete, whereas in the remaining 20% of cases a membrane or diaphragm within the duodenal lumen is responsible for partial (stenosis) or complete occlusion.
During the fifth week of embryonic life, the epithelium of the primitive duodenum proliferates and obliterates the lumen, up to 11 weeks' gestation when vascularization restores the luminal patency. Duodenal atresia is caused by failed recanalization of the duodenum during organogenesis. Another theory suggests an interruption of blood supply during embryogenensis as the main mechanism underlying the condition, although according to some authors a vascular insult leads to atresia of the jejunal and ileum rather than a maldevelopment of duodenum.25
Ancillary Ultrasound Signs
At 18 to 21 weeks' gestation, the only sonographic marker consistent with an abnormal development of duodenum is a dilated stomach with a mild dilatation of the duodenum. During follow-up scans the typical "double bubble" (Figure 17-41A and B) sign becomes more evident, and in the late second to early third trimester polyhydramnios develops. The recognition of polyhydramnios and double bubble sign allows definitive diagnosis of duodenal atresia. When the double bubble is absent but with evidence of a dilated stomach (Figure 17-42), a duodenal stenosis should be suspected.
A: Axial view of a 24-week fetus demonstrates a characteristic double bubble appearance representing the fluid-filled stomach and duodenum. B: Three-dimensional image of duodenum atresia with inversion mode using a combination of "surface" and "gradient light" modes. AO, aorta; C, inferior vena cava.
Transverse scan of the abdomen in a fetus developing a duodenum stenosis. The only ultrasound sign present was a dilated stomach.
The differential diagnosis is posed with enteric duplication cyst, choledochal cyst, and hepatic cyst, which are characterized by noncommunicating anechoic cysts. Therefore, when 2 abdominal anechoic cysts are detected during ultrasound examination, the presence of an inter-cysts communication should be demonstrated in order to distinguish a duodenal atresia from other cystic structures in the middle or right upper abdomen. In addition, 3D imaging may be helpful in differentiating the gastric from the duodenal cavities, and identifying the communication between the pylorus and duodenum. Extrinsic obstruction, duodenal diverticula, and duplication should also be differentiated from a duodenal atresia.
Major structural anomalies associated with duodenal atresia can be found in 40% to 50% of affected fetuses and include gastrointestinal (malrotation, biliary tract disorders, annular pancreas), vertebral (33%), and cardiac defects (30%). A massive overdistension of the stomach and proximal duodenum, and a C-loop sign are indicative of an associated esophageal atresia. Other structural associated anomalies include anorectal malformation and renal anomalies.
The risk of abnormal karyotype, mainly trisomy 21, is very high, since 40% (range 20% to 50%) of fetuses with duodenal atresia are affected with trisomy 21, and 5% to 15% of neonates with Down syndrome have duodenal atresia. In a review of 275 cases of duodenal atresia, Down syndrome was present in 30%, Down syndrome and cardiac malformation in 14%, cardiac anomaly without trisomy 21 in 23%, and other gastrointestinal defects in 42%.26
Fetal karyotype analysis is mandatory. Infants with duodenal atresia and Down syndrome should undergo rectal biopsy to exclude Hirschsprung disease. A detailed survey of fetal anatomy, including echocardiography, should be performed to rule out associated structural anomalies. Postnatal surgery can be performed just after birth and consists of bypass procedures with duodenoduodenostomy or duodenojejunostomy. In the presence of associated intestinal, pancreatic, and biliary anomalies, additional surgical procedures are needed.
In the isolated forms of duodenal atresia, the prognosis is good with an early postoperative mortality rate of 3% to 5% and a late mortality incidence of less than 6%.27 Of the approximately 90% of surviving infants, 25% will undergo an additional surgical procedure at 6 years to resolve a recurrent stenosis or postoperative complications, such as a gastroesophageal reflux. In contrast, the presence of severe biliary tract defects is responsible for 20% to 40% of neonatal mortality.
Long-term sequelae encompass megaduodenum, duodenogastroesophageal reflux, peptic ulcers, and biliary-pancreatic disorders.
The sonographic sign that allows diagnosing duodenal atresia is the double bubble in the upper abdomen.
The double bubble sign appears after 20 weeks' gestation and indicates dilatation of the stomach and duodenum.
Continuity between the 2 anechoic cysts allows differentiation between duodenal atresia and other abdominal cysts.
Detailed survey of fetal anatomy is mandatory, because associated anomalies can be found in 30% to 40% of fetuses with duodenal atresia.
Fetal karyotype should be tested, because 40% of infants with duodenal atresia present trisomy 21.
The prognosis is very good for the isolated form, whereas the association of other structural defects, mainly those involving the biliary tract, is responsible for a higher risk of neonatal mortality.
Jejunoileal Stenosis and Atresia
Jejunoileal atresia is slightly more common than duodenal atresia, occurring in 1 in 3000 to 4000 births. Variation in prevalence between regions has been observed.25
Considered as a whole, the jejunum is slightly more frequently affected (50%) than the ileum (43%) and both of the 2 intestinal tracts are involved in the remaining 7%. Multiple pregnancies and male fetuses are more likely to be affected by the disease than singleton or female fetuses.
Jejunoileal atresia is classified as follows (Figure 17-43):
Type I. Accounts for 20% of cases and is secondary to an intraluminal diaphragm or membrane.
Type II. A fibrous ring connects 2 blind-ending stumps of intestine. This form represents 32% of cases.
Type III. This form consists of 2 portions of intestine, which are completely separated by a mesenteric gap. It occurs in 48% of cases. Type III exists in 2 variants, which carry the worst prognosis because of reduced intestinal surface: type IIIB (11%), which is characterized by the so-called apple-peel aspect of the bowel and involvement of the entire jejunum, proximal ileum, and distal duodenum; and type IV (17%), in which the atresia involves multiple sites.
Classification of jejunoileal atresia. (Top to bottom) Type I: intraluminal diaphragm or membrane with intact bowel (20%). Type II: two blind-ending stumps of bowel connected by a fibrous band (32%). Type III: two completely separated portions of bowel with a mesenteric gap (48%).
Etiological factors are unknown, although animal models have shown that bowel atresia may be due to atresia or torsion of the feeding artery during the rotation of the midgut. The vascular occlusion of a superior mesenteric artery branch may be the underlying mechanism of the apple-peel variant.
Ancillary Ultrasound Signs
The ultrasound diagnosis is based on the visualization of a severe dilatation of the intestinal loops, proximal tothe obstruction (Figure 17-44A and B). In most cases, this sign appears after 25 weeks' gestation. Polyhydramnios is also a late sign and is more likely associated with a proximal lesion. According to nomograms, an ileal loop with transverse diameter greater than 7 mm is suspicious for atresia or stenosis of the small intestine. Additional markers, which could be helpful for diagnosis, are the location of the obstructed loop in the middle of the abdomen, hyperechoic walls (Figure 17-45A), increased peristalsis, and the detection of intraluminal calcifications suggestive of a meconium ileus (Figure 17-45B). The precise site of obstruction (jejunum or ileus) cannot be directly identified by ultrasound, but indirect signs can be demonstrated. In particular, the detection of ascites and/or abdominal calcifications is indicative of intestinal perforation, which is commonly associated with ileal atresia and complicates 6% of cases, whereas the extreme bowel dilatation without signs of perforation is typical of the jejunum atresia.
Transverse view of a third trimester fetus with jejunoileal atresia (A and B). A significant dilation of the small bowel proximal to the obstruction is evident.
Ileal atresia. A: Axial view of the fetal abdomen showing an obstructed loop with hyperechoic walls in the middle of the abdomen. B: In this image, the dilated bowel and intraluminal calcifications suggestive of a meconium ileus are evident.
The differential diagnosis with Hirschsprung disease, meconium ileus, and volvulus is virtually impossible with prenatal assessment, although the loop dilatation is gradual for intestinal atresia and within 3 to 4 days for volvulus. Hydroureter can also mimic a small intestine atresia, and oligohydramnios and/or hydronephrosis are important clues for differential diagnosis. A small bowel atresia has been occasionally described as a cyst-like mass, which needs to be distinguished from ovarian cysts, enteric duplication cyst, and mesenteric cyst.
Jejunoileal atresia/stenosis is usually isolated. In the few cases with multiple malformations, the associated anomalies are represented by the probable cause of atresia (malrotation, volvulus, intestinal duplications, meconium ileus, gastroschisis) in 27%, complications of atresia (intestinal perforation with meconium peritonitis) in 6%, and concurrent bowel defects (colon atresia, esophageal atresia, enteric duplications) in 5%. Cystic fibrosis should also be considered in a fetus with small bowel atresia. The risk of chromosomal defects is not increased in this case; therefore, fetal karyotype analysis is not recommended on the basis of jejunoileal atresia or stenosis.
The progression of jejunoileal atresia is strictly related to the anatomic site of the lesion. Ileal atresia is usually isolated, tends to perforate in utero, and is less frequently associated to preterm delivery compared to jejunal atresia. The detection of abdominal calcifications represents a poor prognostic factor, because it is highly indicative of bowel perforation secondary to ischemia and infarction, which represents the primary complication of small bowel atresia and occurs in 6% of cases. Conversely, jejuneal atresia is usually multiple, tends to dilatation rather than perforation, and is associated with earlier gestational age at delivery and lower birth weight compared with ileal atresia.
Fetal growth restriction can develop, mainly in association with jejunum atresia, secondary to the consequent protein malabsorption. Because of severe polyhydramnios, amniodrainage may be necessary to reduce the risk of preterm delivery. Intestinal atresia is not considered an indication for cesarean delivery, although severe polyhydramnios can lead to malpresentation during labor. The delivery should be performed in a tertiary referral center, because postnatal surgery is to be performed soon after birth. This consists of the removal of the atretic segments and application of end-to-end bowel anastomosis. The prognosis is usually good, except for types IIIB and IV, in which postnatal repair requires a significant reduction of the small intestine length, which consequently leads to malabsorption (short bowel syndrome). Less than 10% of infants are complicated with volvulus, perforation, and meconium peritonitis, which is associated with up to a 10% postoperative mortality rate.
MR images can be useful in identifying the site of intestinal obstruction. Furthermore, when the lesion obliterates multiple sites of small bowel, characteristic signals have been described.28
Prenatal diagnosis of small intestine atresia relies on visualization of dilated bowel after 25 weeks.
A dilated loop greater than 7 mm is suspicious for the presence of small intestine atresia.
Polyhydramnios is indicative of a proximal lesion.
The detection of intraabdominal calcification indicates intestinal perforation, which is typical of ileal occlusion. In contrast, massive dilatation of bowel loops is typically observed in jejunum obstruction.
Small intestine atresia is usually isolated.
Prognosis is generally good, although early preterm delivery due to severe polyhydramnios increases neonatal morbidity and mortality rates.
Anal Atresia and Other Anorectal Abnormalities
Anorectal malformations (ARMs) represent a spectrum of abnormalities ranging from mild anal anomalies to complex cloacal malformations and account for approximately 1 in 5000 live births. ARMs may be subdivided into high, low, and intermediate types according to their relationship with the levator ani muscle.
The abnormal partitioning of the cloaca by the urorectal septum is the underlying mechanism responsible for ARMs.
During the fourth week of human embryonic development, the urogenital system and gastrointestinal system empty into a common draining structure—the cloaca—consisting of the yolk sac derived, distal hindgut, and the allantois.
The caudal end of the cloaca is fused with the intact cloacal membrane, and therefore has no caudal openings. Subsequently, the cloaca is divided into an anterior (urogenital sinus) and a posterior (rectum and the proximal part of the anal canal) part by the developing urorectal septum. The urorectal septum fuses with the cloacal membrane by the seventh week of development dividing it into the ventral urogenital membrane and the dorsal anal membrane. Both urogenital and anal membranes normally rupture around the eighth week of development, creating communications between the anal/urogenital tract and the amniotic cavity.
Failure of perforation of the anal membrane leads to imperforate anus. If the rectum, vagina, and urinary system open to the perineum through a single orifice, a persistent cloaca will develop.
Ancillary Ultrasound Signs
Prenatal diagnosis of ARMs can be suspected when a dilated rectosigmoid intestinal tract is detected, usually from 22 gestational weeks (Figure 17-46), although case reports of imperforate anus as early as 12 gestational weeks have been described.29 However, the majority of ARMs are missed prenatally.30
Axial view of the fetal lower abdomen showing the dilation of the rectosigmoidal intestinal tract.
Occasionally, the meconium in the dilated rectal pouch becomes hyperechoic either proximally or distally to the site of obstruction. Intraluminal calcifications (Figure 17-47) can result from prolonged stasis of the meconium and/or indicate the presence of alkaline urine derived from a colovesical fistula. It is probable that a change of pH causes precipitation of the calcium salt. Enterolithiasis represents a warning sign for large bowel obstruction with or without urorectal fistula.30 Therefore, adequate gastrointestinal and urologic studies must be undertaken after birth for the final diagnosis.
Axial view of the lower fetal abdomen showing the dilated rectal pouch with intraluminal calcifications (arrow). (B, bladder.)
Differential diagnosis is made with the higher bowel obstructions. If the rectal pouch is larger than the filled bladder and appears bilobed, anorectal obstruction is likely. It is noteworthy that, because bowel dilatation may be a transient finding, serial ultrasound examinations are recommended whenever an enlarged bowel is detected.
Persistent cloaca is more commonly seen in the female fetus and is characterized by a single perineal/anal opening that serves as a common outlet for urine and feces to the outside.
Prenatal ultrasound findings may vary considerably and encompass transient fetal ascites, a multiloculated cystic structure arising from the fetal pelvis that may contain debris, bilateral hydronephrosis, dysplastic kidneys, intraluminal colonic calcifications, reduction in amniotic fluid volume, growth retardation, vertebral anomalies, and ambiguous genitalia (Figure 17-48).
Axial view of the lower abdomen showing a clitoromegaly in a fetus with persistent cloaca. Anal atresia and urinary tract anomalies were also associated.
Genitourinary defects occur in approximately 50% of patients with ARMs. Other frequent associated malformations are vertebral anomalies. The sacral segment is the most frequently involved tract including sacral deficiency and hemisacrum. Associated hemivertebrae can involve the thoracic and lumbar tracts, leading to scoliosis. Spinal defects may include a tethered spinal cord, which is the intravertebral fixation of the phylum terminale. This anomaly, which is highly associated with hypodeveloped sacrum and urologic abnormalities, results in motor and sensory disorders. Syringomyelia and myelomeningocele are rarely described in association with anorectal malformations.
The risk of chromosomal anomalies is high, mainly for trisomies 18 and 21. Although the etiology of ARMs is unknown, the mutation of a variety of different genes can manifest with anal defects. Furthermore, anorectal defects are phenotypic of a large spectrum of nonchromosomal syndromes, including VACTERL, MURCS (müllerian duct aplasia, renal aplasia, cervicothoracic somite dysplasia), and OEIS (omphalocele, extrophy, imperforate anus, spinal defect).
All patients with prenatal detection of dilated bowel must be evaluated at birth to rule out associated anomalies. The presence of an abdominal mass is suggestive for a distended vagina (hydrocolpos), which affects 50% of patients with persistent cloaca. Abdominal ultrasound and radiographs of the spine are mandatory in newborns with imperforate anus. At 3 months of age, MR imaging is useful to detect tethered spinal cord and other spinal anomalies.
Prognosis varies widely from minor and easily treated defects to complex and difficult to manage anomalies, which are often associated with other structural malformations and poor functional prognosis. After surgery with sagittal anorectoplasty, neonates are classified into 3 groups on the basis of postoperative complications:
Group I: Poor anatomy, flat bottom, poor quality of muscle, sacral defects, and urinary incontinence. These defects are managed with muscle transfer and/or colostomy.
Group II: Good quality of muscle and normal sacrum, but displaced bowel. The treatment consists in repositioning of the bowel.
Group III: Constipation. Enemas, suppositories, or anterior resection are necessary.
When ARMs are associated with sirenomelia or caudal regression syndrome, the prognosis is very poor due to the associated bilateral renal agenesia.
Anorectal malformations encompass a wide spectrum of disease, which involves the genital, urinary, and gastrointestinal systems.
Although prenatal diagnosis is often missed, overdistension of the bowel and intraluminal calcifications should prompt for suspicion of anorectal malformations.
Because of the high frequency of associated anomalies and syndromes, a detailed survey of fetal anatomy is mandatory when a dilated bowel is detected.
Fetal karyotype is recommended.
Prognosis and quality of life vary widely according to the associated anomalies.