Structural anomalies of the gastrointestinal (GI) and genitourinary (GU) tract arerelatively common. Fetuses with GI or GU anomalies, which often have a goodquality of life after postnatal surgical correction, largely benefit from prenatal diagnosis.

Esophageal atresia is a relatively frequent anomaly, occurring in 1 in 3000–3500live births. It is caused by an impairment in the process of recanalization of theprimitive esophagus. Prenatal diagnosis is suspected when, in the presence of poly-hydramnios (usually after 25 weeks), serial ultrasound examinations fail to demon-strate the fetal stomach, or the stomach appears permanently small (< 15% of theabdominal circumference) (Fig. 22.1); gastric secretions, however, may be sufficientto distend the stomach and make it visible. Also, in the case of an associated fistula,the stomach may look normal. Prenatal diagnosis can therefore often be missed.Factors such as associated anomalies, respiratory complications at birth, gestationalage at delivery, and neonatal weight play the most important prognostic role. Pre-natal diagnosis is crucial, as it permits the paediatrician to be alerted, facilitatesprompt neonatal diagnostic confirmation, and enables prevention of potentiallysevere complications, such as aspiration pneumonia.

Duodenal obstruction occurs in approximately 1 in 7500–10000 live births. It isa sporadic abnormality, although there is an autosomal-recessive pattern of inheri-tance in some cases. Approximately half the fetuses with duodenal atresia have asso-ciated abnormalities, including trisomy 21 in about 40% of cases, and skeletaldefects, gastrointestinal abnormalities, and cardiac and renal defects. Detection oftwo echo-free areas inside the abdomen (“double-bubble” sign), representing thedilated stomach and the first portion of the duodenum, is crucial for prenatal diag-nosis (Fig. 22.2). Polyhydramnios is invariably associated. However, obstruction dueto a central web may result in only a “single bubble” representing the fluid-filledstomach. Postnatal prognosis of duodenal atresia depends mainly on the following:associated anomalies, birthweight, and prompt confirmation of prenatal diagnosis.Survival rate after surgery in patients with an isolated anomaly is higher than 95%.The most frequent site of small bowel obstruction is the distal ileus, followed bythe proximal jejunum. In about 5% of cases, obstructions occur at multiple sites.Although the condition is usually sporadic, in multiple intestinal atresias, familialcases have been described. Associated abnormalities and chromosomal defects arerare. The lumens of the small bowel and colon do not normally exceed 7mm and20mm respectively. Diagnosis of obstruction is usually made late in pregnancy, after25 weeks, because dilation of the intestinal lumen is slow and progressive. Jejunal

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22 Gastrointestinal and genitourinary anomaliesSandro Gabrielli, Nicola Rizzo, and E. Albert Reece

Handbook of Clinical Obstetrics: The Fetus & Mother, Third EditionE. Albert Reece, John C. Hobbins

Copyright © 2007 by Blackwell Publishing Ltd

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Figure 22.1 Cross-section of the abdomen in a fetus with esophageal atresia. Stomach is notvisualized. sp, spine; uv, umbilical vein.

D

st

sp

Figure 22.2 Cross-section of the upper fetal abdomen in a case of duodenal atresia,showing the pathognomonic “double-bubble” sign. D, dilated duodenal bulb; sp, spine; st,stomach.

and ileal obstructions are imaged as multiple fluid-filled loops of bowel in theabdomen (Fig. 22.3). The more distal the site of the obstruction, the greater thenumber of anechoic structures Fetuses with an uncomplicated intestinal obstructioncan be delivered vaginally at term. Induction of labor should be considered whenperforation with ascites occurs. As meconium begins to accumulate in the fetalbowel at 4 months, any perforation occurring after that time could bring the outflowof meconium into the peritoneal cavity. As a result, an intense reaction occurs,leading to extensive adhesions (Fig. 22.4). Polyhydramnios is a frequent finding;ascites may also be present. Prognosis is usually severe. Omphalocele, or exompha-los, occurs in about 1 in 4000 births, and results from failure of normal embryonicregression of the midgut from the umbilical stalk into the abdominal coeloma.Omphalocele is often associated with other abnormalities, as a result of generalinterference with embryonic development during early gestation. It is also associ-ated with an increased risk of chromosomal abnormalities. Prenatal diagnosis isbased on the demonstration of the midline anterior abdominal wall defect, the her-niated sac with its visceral contents, and the umbilical cord insertion at the apex ofthe sac (Fig. 22.5). Isolated lesions have a good prognosis with a survival rate aftersurgery of higher than 90%. Maternal transport to a tertiary center and an accu-rately planned Cesarean delivery would probably avoid the risks of a sudden,

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Figure 22.3 Cross-section of the abdomen in a fetus with small bowel atresia. Dilatedbowel is visible.

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B

sp

Figure 22.4 Cross-section of the fetal abdomen showing a highly hyperechogenic mass(arrow) of meconium peritonitis (cystic type). B, distended loops of bowel; sp, spine.

Figure 22.5 Cross-section of a fetus with omphalocele. Note the herniated hyperechogenicmass (arrow) at the level of cord insertion. L, liver; P, placenta; uc, umbilical cord on top ofthe defect.

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unexpected delivery leading to a delay in surgical care. Gastroschisis is found inabout 1 in 4000 births. In gastroschisis, the primary body folds and the umbilicalring develop normally, and evisceration of the intestine occurs through a smallabdominal wall defect located just lateral and usually to the right of an intact umbil-ical cord. Associated anomalies are uncommon. Prenatal diagnosis is based on thedemonstration of the normally situated umbilicus and the herniated loops of intes-tine, which are free-floating and widely separated (Fig. 22.6). Prognosis hasimproved dramatically during the last three decades. It seems crucial, however, thatdelivery takes place in tertiary-care centers where the neonate can receive intensivecare and where neonatal surgical correction is promptly available.

Bilateral renal agenesis is found in 1 in 5000 births, while unilateral disease isfound in 1 in 2000 births. Renal agenesis derives from failure of development ofthe ureteric bud or nephrogenic blastema, because both components occur at theformation of normal kidneys. This abnormality is usually isolated and sporadic.Failed visualization of kidneys and bladder, associated with oligohydramnios,prompts the diagnosis of bilateral renal agenesis (Fig. 22.7). Bilateral renal agene-sis is a lethal condition. Unilateral agenesis has a favorable prognosis. Multicystickidneys are usually unilateral, although bilateral renal involvement has beenreported. In the majority of cases, this is a sporadic abnormality, but a few exam-ples of familial cases have been described. Multicystic kidney is often associatedwith other congenital anomalies, including mainly congenital heart diseases andchromosomal aberrations (mainly trisomy 18), and it is often part of genetic

Figure 22.6 A case of gastroschisis diagnosed at 22 weeks’ gestation: free-floating loops ofbowel (B) herniated through a lateral abdominal wall defect.

syndromes. Multicystic kidneys are usually unilateral and appear as a cluster of mul-tiple irregular cysts of variable size with little intervening hyperechogenic stroma(Fig. 22.8). Isolated unilateral multicystic kidneys have a good prognosis. Autoso-mal-recessive cystic kidneys invariably involves both kidneys, and occurs in of 1 in20000 live births. Sonographically, both kidneys usually appear extremely enlargedand hyperechogenic (Fig. 22.9). In severe cases, the bladder is absent and oligohy-dramnios is extreme. However, these sonographic appearances may be manifest onlyin late gestation. Prognosis is variable. Autosomal-dominant cystic kidneys almostinvariably affects both kidneys, although often symmetrically. It is usually asymp-tomatic until the third or fourth decade of life. Sonography does not usually demon-strate abnormalities prior to the second or third decade. In a handful of cases,however, affected fetuses have demonstrated findings similar to the autosomal-recessive variety. Kidneys appear grossly enlarged with multiple cysts of variablesize intermixed with well-represented, hyperechogenic solid tissue. The experienceof prenatal diagnosis is limited. It would not seem that intrauterine presentation isnecessarily associated with a poor prognosis. Enlargement of the urinary tractusually occurs, albeit not exclusively as the consequence of obstruction. Mild pyelec-tasia (anteroposterior diameter between 4 and 10mm) has recently been suggestedas a sonographic marker for chromosomal abnormalities and, in some cases, mayreveal vesicoureteric reflux at birth. Hydronephrosis is characterized by dilated renalpelvis and calices (Fig. 22.10).

In cases of megacystis, the bladder is usually greatly enlarged, occupying most ofthe abdomen and distending it. Urethral obstruction can be caused by urethral age-nesis, persistence of the cloaca, urethral stricture, or posterior urethral valves. Withposterior urethral valves, there is usually incomplete or intermittent obstruction of

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A B

Figure 22.7 Color Doppler failed to demonstrate the renal arteries in a case of bilateral (A)and unilateral (B) renal agenesis.

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Figure 22.8 Coronal scan of the trunk of a 33-week fetus with unilateral multicysticdysplastic kidney disease. The cysts are clearly separated by echoic tissue.

Figure 22.9 Coronal section of a fetus with recessive-type polycystic kidneys. Kidneysappear extremely enlarged and hyperechogenic.

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Figure 22.10 Coronal view of the kidney in a case of ureteropelvic junction obstruction.Pelves and calices appear fairly dilated.

the urethra, resulting in an enlarged and hypertrophied bladder with varying degreesof hydroureters, hydronephrosis, a spectrum of renal hypoplasia and dysplasia,oligohydramnios, and pulmonary hypoplasia. The outcome of urethral obstructiondepends on how severe it is and how early it occurs. Complete persistent obstruc-tion occurring in the early midtrimester (e.g., urethral atresia, early posterior ure-thral valves) results in massive distention of the bladder and abdominal wall(prune-belly abdomen), severe oligohydramnios, dysplastic kidneys, and pulmonaryhypoplasia. Shunting of the fetal bladder is feasible, although there is no conclusiveevidence that such intervention improves renal or pulmonary function beyond whatcan be achieved by postnatal surgery. Antenatal evaluation of renal function relieson a combination of ultrasonographic findings and analysis of fetal urine obtainedby puncture of the bladder or renal pelvis. Ovarian cysts are one of the mostcommon causes of abdominal mass in the female neonate. Prenatal ultrasound diag-nosis is possible from the second trimester of pregnancy. Cystic mass in the fetallower abdomen, integrity of GI and GU tracts, and female sex are the main ultra-sound criteria for diagnosis of fetal ovarian cyst. The cyst may be completely fluidor septated and sometimes presents with a fluid-solid level. The cyst may increasein size, decrease, or even disappear, or lead to complications such as torsion, infarction, and rupture. In this light, once prenatal ultrasound diagnosis has been

made, serial examinations should be performed throughout gestation to detect any structural changes in the mass. When sudden development of intense hypere-chogenicity within the mass followed by a complex, heterogeneous appearanceoccurs, immediate delivery is recommended. Conversely, small cysts detected inutero can subsequently disappear and may not be present on a postnatal ultrasoundevaluation.

Further reading

Achiron R, Soriano D, Lipitz S, et al. Fetal midgut herniation into the umbilical cord: improveddefinition of ventral abdominal anomaly with the use of transvaginal sonography. Ultra-sound Obstet Gynecol 1995;6:256.

Aubertin G, Cripps S, Coleman G, et al. Prenatal diagnosis of apparently isolated unilateralmulticystic kidney: implications for counseling and management. Prenat Diagn2002;22:388.

Baerg J, Kaban G, Tonita J, et al. Gastroschisis: a sixteen-year review. J Pediatr Surg 2003;38:771.

Blazer S, Zimmer EZ, Gover A, et al. Fetal omphalocele detected early in pregnancy: associated anomalies and outcomes. Radiology 2004;232:191.

Brantberg A, Blaas HG, Salvesen KA, et al. Surveillance and outcome of fetuses with gastroschisis. Ultrasound Obstet Gynecol 2004;23:4.

Haeusler MC, Berghold A, Stoll C, et al. prenatal ultrasonographic detection of gastrointesti-nal obstruction: results from 18 European congenital anomaly registries. Prenat Diagn2002;22:616.

Jouannic J, Hyett Jon A, Pandya PP, et al. Perinatal outcome in fetuses with megacystis in thefirst half of pregnancy. Prenat Diagn 2003;23:340.

Rizzo N, Gabrielli S, Perolo A, et al. Prenatal diagnosis and management of fetal ovarian cysts.Prenat Diagn 1989;9:97.

Romero R, Ghidini A, Gabrielli S, et al. Gastrointestinal tract and abdominal wall defects. In:Brock DJH, Rodeck CH, Ferguson-Smith MA, eds. Prenatal diagnosis and screening.Edinburgh: Churchill Livingstone; 1992:227.

Roume J, Ville Y. Prenatal diagnosis of genetic renal diseases: breaking the code. UltrasoundObstet Gynecol 2004;24:10.

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23 Fetal skeletal anomaliesLuís F. Gonçalves, Patricia Devers, Jimmy Espinoza, and Roberto Romero

Skeletal dysplasias are a heterogeneous group of disorders that affect the develop-ment of chondro-osseous tissues, resulting in abnormalities in the size and shape of