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Case Report |
1
Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline
Ave., Boston, MA 02215.
2
Department of Obstetrics and Gynecology, Beth Israel Deaconess Medical Center,
Boston, MA 02215.
3
Department of Surgery, Children's Hospital, 300 Longwood Ave., Boston, MA
02215.
4
Department of Radiology, Children's Hospital, Boston, MA 02215.
Received May 23, 2000;
accepted after revision June 23, 2000.
Address correspondence to D. Levine.
Introduction
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The appearance of bronchogenic duplication cysts has been described in utero as an anechoic unilocular intrathoracic cyst [3, 4]. In one fetus, the enlarged, uniformly echogenic obstructed lung, not the obstructing cyst, was the lesion seen prenatally [5]. A bronchogenic cyst causing a fluid-filled obstructed lung has also been previously described in a newborn [2]. To our knowledge, the antenatal diagnosis of a mediastinal bronchogenic duplication cyst leading to unilateral and then bilateral bronchial obstruction has not previously been reported. The prenatal diagnosis in this case allowed life-saving ex utero intrapartum treatment including placement onto extracorporeal membrane oxygenation therapy while the fetus was still under placental perfusion and resection of the obstructing lesion followed by airway reconstruction performed during the first hours of life.
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When the fetus was at 30 weeks' gestation, in addition to the echogenic lung mass, a moderate mediastinal shift to the right was detected. Additional sonographic findings at this time were macrosomia (with the size of the fetus at 4 weeks' gestation greater than that expected) and moderate polyhydramnios with an amniotic fluid index of 28. No left lung mass was identified to explain the mediastinal shift. Because of this unexpected finding, a second sonogram and MR image were obtained at 31 weeks 4 days' gestational age (Figs. 1C,1D,1E,1F). The MR image again showed a mass just behind the atria of the heart in the region of the carina. The mass had a bilobed appearance and was of high signal intensity on T2-weighted imaging and dark on T1-weighted imaging. The right lung was compressed with a mediastinal shift to the right. The right lung was of lower signal intensity than expected, which was thought to result from compression. The left lung appeared hyperinflated with stretched vessels. The lung parenchyma protruded between the ribs. The findings were best explained by a complex cystic mediastinal mass, likely a bronchogenic cyst, causing obstruction of the left main stem bronchus leading to hyperinflation of the left lung. The compressed right lung and hyperinflated obstructed left lung raised concerns about the ability of the neonate to breathe after birth. Because a well-controlled, planned delivery was necessary for this fetus, an ex utero intrapartum treatment procedure was planned for delivery at 34 weeks. During this procedure the fetus is partially delivered and while on placental support, diagnostic and therapeutic maneuvers can be performed.
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One week later, the patient presented to labor and delivery with preterm contractions. The contractions were controlled with magnesium sulfate. Large-volume amniocentesis (1200 mL) was performed to relieve the patient's discomfort and decrease uterine distention. Because of concern about potential change in the appearance of the lungs, sonography and MR imaging were again performed before the ex utero intrapartum treatment procedure. In addition to the previously seen echogenic mediastinal mass, a 12-mm anechoic cyst was now visualized just below the aortic arch on sonography. MR images documented decreased mediastinal shift to the right compared with the prior examination, which had been performed 10 days previously (Fig. 1G). The left lung was still hyperexpanded, but it had less herniation to the right side. In addition, the right lung had increased signal intensity compared with the prior study. These findings could be explained by maturation of the lungs with reabsorption of excess left lung fluid, giving more room for the right lung to expand. More worrisome was the possibility that the right lung was now also obstructed and therefore beginning to accumulate more fluid. If allowed to progress unabated, this complication could lead to cardiac compression and hydrops.
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Because of concern regarding bilateral bronchial obstruction, the ex utero intrapartum treatment procedure was performed at 33 weeks' gestation. While the fetus remained attached to the placental circulation, bronchoscopy was performed, which revealed a thinwalled cyst obstructing the distal trachea and both mainstem bronchi at the carina. Fluid was seen filling the otherwise normal airways distal to the cyst. Endotracheal tube intubation beyond the obstructing lesion was thought to be a poor option because only one mainstem bronchus could be intubated. In addition, obstructed lungs in utero contain low levels of surfactant, which makes ventilation difficult. The fetus was put on extracorporeal membrane oxygenation before the umbilical cord was divided. A CT scan obtained with contrast material was used to evaluate the vessels around the lesion. This examination showed similar findings to those of the MR examination, with a cystic nonenhancing lesion forming a U beneath the carina, a mediastinal shift to the right, a hyperexpanded fluid-filled left lung, and a fluid-filled right lung with volume loss. The cyst was resected via an open right thoracotomy. A complex 1.5 x 1.0 cm cyst was found interdigitating between and compressing the rings of the trachea and mainstem bronchi. After the cyst was removed, the carina was reconstructed.
Postoperatively, the neonate did well. She was taken off extracorporeal membrane oxygenation at 4 days, was extubated at 7 days, and was discharged in good health at 2 weeks.
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This case is of interest for a number of reasons. First, this bronchogenic cyst had an echogenic appearance on sonography, which suggested a different cause of the lesion such as a congenital cystic adenomatoid malformation. This case emphasized the need to include mediastinal masses and cysts in the differential diagnosis when a centrally located thoracic mass is visualized, despite an echogenic appearance. The echogenic appearance of the lung may have been caused by a small area of obstructed lung rather than the bronchogenic cyst itself.
A second reason this case is of interest is the development of obstruction with a mediastinal shift toward the side of the presumed mass. Typically when a fetal mediastinal shift is visualized, it is assumed that the shift is away from the side of a large mass lesion. In this case, no left-sided mass was initially visualized sonographically. Either a new mass, isoechoic to the lung, was present on the left, or a central obstruction was present. Use of prenatal MR imaging was crucial in making the diagnosis because the MR examination defined the hyperexpanded left lung and the bronchogenic cyst. The prenatal diagnosis of a bronchogenic cyst was suggested at the time of the second MR examination because bronchogenic cysts are the most common subcarinal mass lesion [7].
The third interesting finding in this case was the rapid change in the appearance of the lungs over a period of 10 days. The third MR examination revealed that although the left lung had decreased in size, there was a rapid increase in size and signal intensity (on T2-weighted imaging) in the otherwise small right lung. This signal intensity was similar to that of the obstructed left lung, suggesting new bilateral obstruction.
A final comment on this case regards the use of prenatal MR imaging for improved fetal diagnosis. MR imaging has been shown to be useful as an adjunct to sonography in the evaluation of fetal chest masses [8]. In our patient, MR imaging allowed visualization of a mediastinal cyst that was not adequately characterized on sonography. Although MR imaging is not expected to replace sonography for routine fetal screening and diagnosis, MR imaging should be considered when a complex mass in the thorax that requires further elucidation before delivery is visualized.
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