Differential diagnosis:
This was not a right diaphragmatic hernia because the liver was in place in the abdomen surrounded by ascites.
This was not a cystic adenomatoid malformation of the lung type III (CCAML III) because energy Doppler indicated a normal distribution of the pulmonary vessels into the right thoracic mass.
Thus tracheal stenosis was thought of. But, because the heart was completely shifted to the left, the diagnosis of right bronchus atresia was proposed prenatally and was confirmed by pathology.
To our knowledge, this is the first reported case of unilateral bronchial atresia diagnosed by ultrasound in the second trimester of pregnancy.
Discussion:
The first prenatal diagnosis of laryngo-tracheal obstruction was reported in1989 [1]. This is a rare anomaly. In 2000, only 12 such prenatally diagnosed cases had been reported [2].
Upper respiratory tract obstruction is usually associated with bilateral enlarged uniformly hyperechogenic lungs. The diaphragmatic is inverted, bulging downwards into the abdomen.
The presence of fluid-filled trachea and bronchi indicates laryngeal atresia.
Kalache & al. [3] studied ultrasound measurements of the trachea, larynx and pharynx throughout gestation, as a mean to diagnose upper respiratory obstructive anomalies tract. He noted that in fetuses with laryngeal atresia only the tracheal diameter was significantly higher compared with that of normal fetuses.
As in our case, Okamura & al. [4] reported color Doppler findings as the most important characteristic for distinguishing fetal upper respiratory obstruction from other echogenic changes in the fetal chest such as CCAML III. They underlined the increased blood flow but they did not emphasize, as we do, the integrity of the pulmonary vessels architecture into the thoracic mass. We believe this point essential to eliminate two differential diagnoses: CCAML III and lung sequestration.
In all published cases, upper respiratory obstruction was associated with ascites or fetal hydrops, which were interpreted as a sign of congestive (right) heart failure. Doppler flow measurements to the inferior vena cava, umbilical vein and ductus venosus showed signs of compromised fetal circulation [6].
The volume of amniotic fluid can be normal, as in our case.
Kassanos & al. [5] suggest that oligohydramnios (due to the obstructed drainage of lung liquid) may be helpful in distinguishing the upper respiratory tract obstruction from CCAML III.
In some cases, polyhydramnios might result from esophagus compression.
Associated syndromes:
Laryngo-tracheal atresia may be part of different syndromes: Fraser, Di George, VATER association, and rhizomelic chondrodysplasia punctata.
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Fraser syndrome: autosomal recessive, cryptophthalmia, syndactyly and other anomalies like laryngeal atresia, genito-urinary tract anomalies. In a review [6] of 16 Fraser cases, 8 were diagnosed prenatally with hyperechoic lungs, oligohydramnios, and ascites.
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Di George: 22q11 microdeletion, conotruncal-cardiopathy with thymus aplasia or hypoplasia, parathyroid hypoplasia. Laryngeal atresia has been described in 3 neonates with DiGeorge anomaly [7].
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The combination of a VATER-association with tracheal atresia has only been reported twice [8].
Conclusions:
Upper respiratory tract obstruction is uncommon in fetal life. Yet, the diagnosis is feasible prenatally by ultrasound: enlarged hyperechoic lungs associated with ascites or hydrops.
Energy Doppler, by demonstrating the integrity of the pulmonary vessels architecture into the thoracic mass, may be helpful to eliminating two differential diagnoses: CCAML III and lung sequestration for which the prognosis might be quite different.
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3 Kalache KD, Franz M, Chaoui R, Bollmann R . Ultrasound measurements of the diameter of the fetal trachea, larynx and pharynx throughout gestation applicability to prenatal diagnosis of obstructive anomalies of the upper respiratory-digestive tract. Prenat diagnosis 1999 Mar; 19(3): 211-8
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8 Baarsma R, Bekedam DJ, Visser GH. Qualitative abnormal fetal breathing movements associated with tracheal atresia. Early hum Dev 1993 Feb; 32(1): 63-9