Case Report
Women's Imaging
January 2007

Prenatal Tracheal Obstruction Due to Double Aortic Arch: A Potential Mimic of Congenital High Airway Obstruction Syndrome

Double aortic arch is a relatively common congenital anomaly of the aortic arch system resulting from failed regression of the fourth pharyngeal arch arteries. Symptoms develop postnatally due to compression of the trachea and esophagus, which are encircled by the left and right aortic arches. The classic history is noisy breathing during the first few weeks of life, and the diagnosis is usually confirmed by postnatal echocardiography or MRI. Prenatal diagnosis is rare [1, 2], and double aortic arch has not been previously described as a cause of prenatal tracheal obstruction, to our knowledge.
Congenital high airway obstruction syndrome (CHAOS) is a recognized cause of prenatal central airway obstruction due to intrinsic atresia or stenosis of the larynx or upper trachea. CHAOS causes pulmonary overdistention due to retained bronchial secretions. Increased intrathoracic pressure with impaired venous return is believed to account for the associated development of fetal hydrops. The resulting constellation of large echogenic lungs with flattening or inversion of the diaphragm, dilated fluid-filled airways below the level of obstruction, and fetal hydrops or ascites is considered characteristic of CHAOS on prenatal sonography. Untreated CHAOS inevitably leads to fetal demise or stillbirth [3-5].
We present a case of double aortic arch that caused prenatal central airway obstruction and that mimicked CHAOS on fetal echocardiography and MRI.

Case Report

A 26-year-old pregnant woman (gravida 1, para 0) was referred to our institution for management of suspected fetal CHAOS after a routine detailed obstetric sonogram at 22 weeks' gestation showed fetal ascites and enlarged echogenic lungs (Fig. 1A). The four-vessel view of the heart was normal. A repeat sonogram at 24 weeks' gestation confirmed the findings of pulmonary enlargement with fetal hydrops and ascites, but dilated airways were not seen and the central airway was considered normal.
In view of these atypical features, MRI was performed at 24 weeks' gestation, confirming the presence of ascites and pulmonary overexpansion. In addition, MRI showed mildly dilated intrapulmonary airways with apparent narrowing of the central airway between the thoracic inlet and the carina (Figs. 1B and 1C). The central airway appeared otherwise patent without intrinsic occlusion (Fig. 1D). The possibility of extrinsic vascular compression was raised and was subsequently confirmed on fetal echocardiography, which showed a double aortic arch with a dominant right arch, a smaller left arch, and left ductal arch forming a ring surrounding the trachea (Figs. 1E and 1F). On pulsed Doppler interrogation, left and right ventricular inflow patterns and flow patterns in the inferior vena cava (no increase in a reversal), ductus venosus (no a wave reversal), and umbilical vein (no pulsations) appeared normal. The diagnosis was further confirmed by the presence of mirror image bifurcated brachiocephalic arteries in the same plane, cephalad to the aortic arch (Fig. 1G).
A female infant was delivered vaginally at 30 weeks' gestation after spontaneous preterm labor. The infant required immediate intubation for respiratory insufficiency. Extubation was not possible until the nondominant arch was surgically divided at 6 weeks of age. Subsequent postoperative recovery was uneventful.

Discussion

Prenatal central airway obstruction can lead to fetal demise or stillbirth and can be due to intrinsic airway defects (collectively termed “CHAOS”) or extrinsic compression by neck masses or vascular rings. The recognition of CHAOS on prenatal sonography may allow life-saving airway management by the ex utero intrapartum treatment or by in utero tracheotomy [6, 7]. The impressive imaging findings that develop due to the airway obstruction in CHAOS (pulmonary overexpansion, distal airway dilatation, and fetal hydrops or ascites) have not been previously reported with extrinsic compression by tumors or vascular rings, although such congenital abnormalities are a recognized cause of postnatal airway obstruction. Prenatal sonography or MRI may depict these conditions, but polyhydramnios (presumably due to impaired fetal swallowing) is the only reported finding suggestive of prenatal airway or esophageal obstruction.
Fig. 1A 26-year-old pregnant woman (gravida 1, para 0) was referred to our institution for management of suspected fetal congenital high airway obstruction syndrome. Sagittal sonogram obtained at 22 weeks' gestation shows echogenic lung (L) and flattened diaphragm (arrow). A = anterior, P = posterior.
Fig. 1B 26-year-old pregnant woman (gravida 1, para 0) was referred to our institution for management of suspected fetal congenital high airway obstruction syndrome. Sagittal T2-weighted single-shot fast spin-echo MR image obtained at 24 weeks' gestation shows enlarged left lung (L) causing flattening of left hemidiaphragm (white arrows). Mildly dilated bronchus (black arrow) is seen in left lower lobe. Large volume of ascites (asterisk) is visible below diaphragm.
Fig. 1C 26-year-old pregnant woman (gravida 1, para 0) was referred to our institution for management of suspected fetal congenital high airway obstruction syndrome. Coronal T2-weighted single-shot fast spin-echo MR image obtained at 24 weeks' gestation shows apparent narrowing (arrow) of central airway superior to carina and inferior to thoracic inlet. Right lung (RL) and heart (asterisk) are easily visualized in this magnified image.
Fig. 1D 26-year-old pregnant woman (gravida 1, para 0) was referred to our institution for management of suspected fetal congenital high airway obstruction syndrome. Sagittal T2-weighted single-shot fast spin-echo MR image obtained at 24 weeks' gestation shows continuity between fetal trachea (thick white arrow) and oropharynx (black arrow), without evidence of high airway occlusion. Thin white arrow denotes continuity between pharynx and trachea.
Fig. 1E 26-year-old pregnant woman (gravida 1, para 0) was referred to our institution for management of suspected fetal congenital high airway obstruction syndrome. Transverse cross-sectional image above level of three-vessel view [10] obtained at 24 weeks' gestation shows dominant right arch and smaller left arch arising above level of left ductus arteriosus, with trachea located centrally (arrow). LAA = left aortic arch, RAA = right aortic arch.
Fig. 1F 26-year-old pregnant woman (gravida 1, para 0) was referred to our institution for management of suspected fetal congenital high airway obstruction syndrome. Doppler color flow image of E confirms patency of aortic ring formed by double aortic arch. This vascular anomaly was not visible on MRI but was well seen on sonography. LAA = left aortic arch, RAA = right aortic arch.
Fig. 1G 26-year-old pregnant woman (gravida 1, para 0) was referred to our institution for management of suspected fetal congenital high airway obstruction syndrome. Transverse cross-sectional image obtained at 24 weeks' gestation using consecutive sweep farther cephalic than E shows mirror image bifurcated brachiocephalic arteries in same plane, with left carotid and subclavian arteries indicated by leftmost arrows and subclavians posteriorly (two rightmost arrows). A = anterior.
In this case, the fetus had dramatic sonographic findings that mimicked those of CHAOS and that were presumably causing airway obstruction. These findings could have prompted an inappropriate intervention such as an in utero tracheotomy. Fetal MRI was helpful in precisely localizing the level of airway narrowing and raising the possibility of extrinsic vascular compression. Fetal echocardiography revealed the specific cause of extrinsic compression—the presence of a double aortic arch.
This case highlights the need to critically review imaging findings in apparent CHAOS cases on prenatal sonography. Atypical features should lead to further imaging with fetal MRI or fetal echocardiography because these techniques may help identify extrinsic vascular anomalies, such as the double aortic arch seen in this case. Recognition that double aortic arch may mimic CHAOS on prenatal sonography may prevent misdiagnosis and facilitate appropriate treatment.
The present case is of interest for a second reason. It has been proposed that the cause of hydrops in CHAOS is secondary to cardiac compression with impedance of systemic venous (including umbilical venous) return. The absence of Doppler flow changes consistent with compression and increased central venous pressure—including dominant e wave in ventricular filling, increased a wave reversal in the inferior vena cava, a wave reversal in the ductus venosus, and umbilical venous pulsation [8, 9]—suggested another mechanism for the hydrops. Perhaps with significant lung expansion and inversion of the diaphragms, there may be impedance of lymphatic return through the thoracic duct resulting in abdominal lymphatic congestion and the evolution of ascites, which was the primary extrathoracic finding in our case.

Footnotes

Address correspondence to F. V. Coakley.
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References

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Yoo SJ, Min JY, Lee YH, Roman K, Jaeggi E, Smallhorn J. Fetal sonographic diagnosis of aortic arch anomalies. Ultrasound Obstet Gynecol 2003; 22:535-546
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Achiron R, Rotstein Z, Heggesh J, et al. Anomalies of the fetal aortic arch: a novel sonographic approach to in-utero diagnosis. Ultrasound Obstet Gynecol 2002; 20:553-557
3.
Paek BW, Callen PW, Kitterman J, et al. Successful fetal intervention for congenital high airway obstruction syndrome. Fetal Diagn Ther 2002; 17:272-276
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DeCou JM, Jones DC, Jacobs HD, Touloukian RJ. Successful ex utero intrapartum treatment (EXIT) procedure for congenital high airway obstruction syndrome (CHAOS) owing to laryngeal atresia. J Pediatr Surg 1998; 33:1563-1565
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Goldstein RB. Ultrasound of the fetal thorax. In: Callen PW, ed. Ultrasonography in obstetrics and gynecology. Philadelphia, PA: Saunders, 2000:447-448
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Mychaliska GB, Bealer JF, Graf JL, Rosen MA, Adzick NS, Harrison MR. Operating on placental support: the ex utero intrapartum treatment procedure. J Pediatr Surg 1997; 32:227-231
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Hedrick MH, Ferro MM, Filly RA, Flake AW, Harrison MR, Adzick NS. Congenital high airway obstruction syndrome (CHAOS): a potential for perinatal intervention. J Pediatr Surg 1994; 29:271-274
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Fontes-Pedra SRF, Smallhorn J, Ryan G, et al. Fetal cardiomyopathies: etiologies, hemodynamic findings, and clinical outcome. Circulation 2002; 106:585-591
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Mahle WT, Rychik J, Tian ZY, et al. Echocardiographic evaluation of the fetus with congenital cystic adenomatoid malformation. Ultrasound Obstet Gynecol 2000; 16:620-624
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Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: W82 - W85
PubMed: 17179331

History

Submitted: March 1, 2005
Accepted: May 29, 2005

Keywords

  1. airway
  2. aorta
  3. cardiovascular imaging
  4. congenital anomaly
  5. fetal imaging
  6. MRI
  7. trachea

Authors

Affiliations

Dorothy J. Shum
Department of Radiology, University of California San Francisco, Box 0628, M-372, 505 Parnassus Ave., San Francisco, CA 94143-0628.
Matthew S. Clifton
Department of Surgery, University of California San Francisco, San Francisco, CA 94143-0628.
Fergus V. Coakley
Department of Radiology, University of California San Francisco, Box 0628, M-372, 505 Parnassus Ave., San Francisco, CA 94143-0628.
Lisa K. Hornberger
Department of Pediatrics, Fetal Cardiovascular Program, University of California San Francisco, San Francisco, CA 94143-0628.
Bonnie N. Joe
Department of Radiology, University of California San Francisco, Box 0628, M-372, 505 Parnassus Ave., San Francisco, CA 94143-0628.
Ruth B. Goldstein
Department of Radiology, University of California San Francisco, Box 0628, M-372, 505 Parnassus Ave., San Francisco, CA 94143-0628.
Michael R. Harrison
Department of Surgery, University of California San Francisco, San Francisco, CA 94143-0628.

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