Thoracic Mass on Fetal Ultrasound

• Congenital pulmonary airways malformation (CPAM): Most common of the congenital thoracic masses. Imaging appearance depends on the nature of the cysts. Fetal ultrasound of large-cyst CPAMs have variable-sized anechoic lesions intertwined with echogenic soft tissue. At fetal MR, there are T2-hyperintense unilocular or multilocular lesions with discrete walls. Small-cyst CPAMs are echogenic with multiple small cysts and have a variable appearance on T2-weighted images depending on the cystic and solid components. Microcystic CPAMs are homogeneously echogenic and are homogeneously hyperintense solid masses on T2-weighted images.
• Bronchopulmonary sequestration: Extralobar form presents as a homogeneous hyperechoic mass in a paraspinal location, usually in the left lower thorax, mimicking a microcystic CPAM. A feeding artery originating from the descending aorta at color Doppler helps distinguish the two. On MR, extralobar sequestration presents as a solid, well-defined, uniformly hyperintense mass on T2-weighted images. Intralobar sequestration is usually diagnosed in childhood or adulthood.
• Hybrid lesion: Combination of CPAM with bronchopulmonary sequestration. The image above demonstrates a T2-hyperintense lesion in the right hemithorax. Pathology showed combined features of intralobar sequestration and congenital pulmonary adenomatoid malformation.
• Congenital lobar emphysema: Collapsed airway acts as a one-way valve, resulting in air trapping and expanded alveoli with intact walls. The intact alveolar walls make the term emphysema technically inaccurate, and some people refer to this condition as congenital lobar overinflation. Left upper lobe is involved in about 50% of cases. Fetal ultrasound may show a homogeneously hyperechoic mass that is homogeneously high signal on T2-weighted images.
• Congenital diaphragmatic hernia: Usually left sided. Look for stomach and bowel next to the heart.
• Congenital high airway obstruction syndrome: Rare. Caused by laryngeal or tracheal atresia, tracheal stenosis or web, or extrinsic compression (e.g., double aortic arch). Results in outflow obstruction of the fetal lung fluid and pulmonary hyperplasia. Prenatal US shows symmetrically enlarged echogenic lungs, dilated and fluid-filled trachea and bronchi, and inverted hemidiaphragms. The large lungs compress and anteriorly displace the heart. Fetal MRI shows enlarged, T2-hyperintense lungs with flattened or inverted hemidiaphragms.
• Bronchial atresia: Rare. Focal obliteration of a segmental, subsegmental, or lobar bronchus with dilated and mucus-filled bronchi distal to the stenosis. There will be an echogenic lesion that is homogeneously high signal on T2-weighted images.
• Bronchogenic cyst: Foregut duplication cysts. Usually in the mediastinum near the carina, but may occur within the lung parenchyma, pleura, or diaphragm.
• Cystic teratoma:

References

Biyyam DR, Chapman T, Ferguson MR, Deutsch G, Dighe MK. Congenital lung abnormalities: embryologic features, prenatal diagnosis, and postnatal radiologic-pathologic correlation. Radiographics. 2010 Oct;30(6):1721-38.