Case of the Week # 502

Case of the Week # 502

Javier Cortejoso
 on 04/06/2023
 on Thursday, April 6th, 2023
The ultrasound images demonstrate the following findings:
• Image 1, Videos 1-2: show axial sections of the fetus in which the heart is deviated towards the right hemithorax. The axis and morphology of the heart are completely normal. Behind the heart is the right lung. A heterogeneous echogenic mass within the anterior part of the left hemithorax, possibly representing non-dilated small bowel loops, causes this displacement. Behind this heterogeneous zone is a homogeneous, hypoechoic structure, which could correspond to the liver or spleenThe stomach is located inferior to the heart and mass.
• Video 3: parasagittal section through the fetal thorax and abdomen shows a curved hypoechoic line, convex toward the thorax, that is possibly the anterior part of the diaphragm. This line reaches the stomach and localizes the defect in the posterior diaphragm. Through the defect, there is herniation of echogenic bowel (and liver?) into the fetal chest. Color Doppler images show displacement of superior mesenteric artery or less likely, umbilical and hepatic vessels into the fetal chest.

The presence of a fetal chest mass should be suspected when the fetal heart is deviated from its expected normal position. The chest mass may be cystic, solid, or a combination of both. The most common fetal chest mass is displaced abdominal viscera resulting from a diaphragmatic hernia, followed by congenital pulmonary airway malformation, pulmonary sequestration, bronchogenic cyst, and bronchial atresia. Pleural effusions also can cause mass effect. These entities can be differentiated on the basis of their sonographic appearance.

Congenital diaphragmatic hernia (CDH) is characterized by a defect in the diaphragm leading to the protrusion of abdominal contents into the thoracic cavity affecting the normal development of the lungs. The prevalence of congenital diaphragmatic hernia based on the available literature is approximately 1 in 2500 pregnancies and 1 in 5000 live births. The condition may present as an isolated lesion or as part of a syndrome. The most common associated chromosomal abnormalities are trisomies 13, 18, 21 and tetrasomy 12 p. Congenital diaphragmatic hernia is the most common finding in Fryns syndrome and can also be part of Brachmann-Cornelia De Lange, Beckwith-Wiedemann, Simpson-Golabi-Behmel, Goltz, Denys‐Drash, Gershoni‐Baruch, Cantrell's pentalogy and others. Posterolateral hernias, also known as Bochdalek hernias, are the most common type (70–75%) with the majority occurring on the left side (85%) and less frequently on the right side (13%) or bilateral (2%). Rarer forms include anterior defects, also known as Morgagni hernias (23–28%), and central or hiatus hernias (2–7%). The defect may range from a small opening of the posterior muscle rim to complete absence of diaphragm. Unlike Bochdalek-type hernias, most foramen of Morgagni hernias have a well-defined hernia sac. The defect in the diaphragm causes the abdominal viscera to herniate into the thoracic cavity. Herniation of viscera into the thoracic cavity results in abnormal lung development on the ipsilateral side with variable effect on the contralateral side. Pulmonary hypoplasia results in abnormal pulmonary vasculature resulting in persistent pulmonary hypertension leading to right ventricular dysfunction. A complete absence of the diaphragm may occur resulting in diaphragmatic agenesis and severe lung hypoplasia.

Most hernias are first suspected at the 18th to 22nd weeks of gestation, but they have been identified as early as the first trimester of pregnancy. The ultrasound diagnosis of congenital diaphragmatic hernia is typically indirect, with the identification of the abnormal intrathoracic position of the stomach and/or other migrated viscera, and the displacement of the heart in the mediastinum. In bilateral diaphragmatic hernias, the left-to-right midline shift of the heart is minimal. Sagittal and parasagittal views can detect a tortuous path of the inferior vena cava and the absence of the hypoechoic contour of the diaphragm. A cephalad orientation of the superior mesenteric artery strongly supports the diagnosis of congenital diaphragmatic hernia. The presence of a fluid-filled stomach in the chest is easily recognized, but diaphragmatic hernias in which the stomach is located in the abdomen are more difficult to correctly diagnose as the bowel, liver, and lung may have a similar sonographic appearance. In the few cases in which the stomach does not migrate into the thorax, the appearance of the bowel and the spleen may be that of an inhomogeneous hyperechoic mass in the left hemithorax. Real-time images may demonstrate peristalsis, allowing for recognition of herniated bowel. Paradoxical motion of the hemidiaphragm with fetal breathing movements is diagnostic of a diaphragmatic abnormality. It consists of a downward movement of the abdominal organs on the normal side, and an upward movement of the herniated abdominal contents into the chest during fetal inspiration. Pleural effusions are not uncommon with congenital diaphragmatic hernia and are seen much more often with right-sided than with left-sided hernias. Interestingly, if pleural effusions are noted in a fetus with suspected left-sided congenital diaphragmatic hernia, the possibility of diaphragmatic eventration should be raised, as over half of fetuses with eventration will have pleural and pericardial effusions. Pleural effusions communicate with the peritoneal cavity through the diaphragmatic defect, and in half of cases with congenital diaphragmatic hernia and pleural effusion, peritoneal fluid is also seen. A hernia sac is a pleuroperitoneal sac covering and enclosing the herniated organs in the thorax. By ultrasound and magnetic resonance imaging, the smooth convex interface suggestive of a hernia sac stands in contrast to the irregular interface typically observed in congenital diaphragmatic hernia without a hernia sac. Polyhydramnios frequently accompanies congenital diaphragmatic hernia but is usually a late finding, seen most often in the third trimester.

Associated nonsyndromic structural anomalies can include in descending order of frequency: cardiovascular, genitourinary, central nervous system, musculoskeletal, gastrointestinal, and chest abnormalities. About 10% of patients with congenital diaphragmatic hernia present with additional gastrointestinal pathologies. Intestinal herniation may cause distortion of the vascular axis resulting in impaired flow, vascular congestion, mesenteric volvulus, and/or ischemia in utero or after birth. The outcomes in congenital diaphragmatic hernia depends on the presence of associated anomalies (especially heart disease), the extent of lung hypoplasia, and the position of the liver. The presence of a hernia sac is associated with a higher pulmonary volume and a better overall prognosis.

Diaphragmatic eventration is characterized by the cephalic displacement of all or a portion of an intact diaphragm owing to a weakness believed to be secondary to defective diaphragmatic muscularization. It accounts for 5% of all congenital diaphragmatic defects, is more common on the right side, and is not associated with severe lung hypoplasia. Typical prenatal ultrasound findings are the existence of an abnormal intrathoracic mass, cardiac axis or mediastinal shift and polyhydramnios. A partial elevation of a hemidiaphragm with a normal position of the uninvolved part should suggest the diagnosis, but the thinned membrane is not always detected.

The differential diagnosis of congenital diaphragmatic hernia includes any intrathoracic lesion that displaces the fetal heart or lungs, including cystic (i.e., congenital pulmonary airway malformation; bronchogenic, enteric, and neuroenteric cysts; and thymic cysts) and solid lesions (mediastinal teratoma, bronchopulmonary sequestrations, tracheal/bronchial atresia, and even an obstructive mucous plug). In these conditions, the intraabdominal organs are not displaced to the thorax. Multiple cystic lesions in the chest are more likely to be congenital pulmonary airway malformation than congenital diaphragmatic hernia, and a presence of a systemic feeding vessel to a cystic or solid mass is consistent with a bronchopulmonary sequestration. Congenital pulmonary airway malformation type III (microcystic) presents as a solid-appearing, bulky, echogenic lung mass. The mass appears solid because the sound beam traverses multiple interfaces caused by the walls of myriad tiny cysts. Pulmonary sequestrations typically are echogenic, homogeneous, and well-defined masses that tend to occur in in the posterior basilar segment of the lungs, usually on the left side. Color Doppler investigation of this mass shows a feeding vessel originating from the descending aorta, which allows differentiation from type III Congenital pulmonary airway malformation.

Suggested readings:
• Alamo L, Gudinchet F, and Meuli R. Imaging findings in fetal diaphragmatic abnormalities. Pediatr Radiol 2015; 45: 1887-1900
• Berman DR, Treadwell MC. Ultrasound Evaluation of the Fetal Thorax. In: Norton ME, Scoutt LM, and Feldstein VA, ed. Callen’s Ultrasonography in Obstetrics and Gynecology, 6th ed. Elsevier Inc., Philadelphia, PA, USA, 2017; pag 346-370
• Chandrasekharan PK, Rawat M, Madappa R, et al. Congenital Diaphragmatic hernia – a review. Maternal Health, Neonatology, and Perinatology (2017) 3: 6 DOI 10.1186/s40748-017-0045-1
• Comstock C, Bronsteen RA, Whitten A, et al. Paradoxical motion: a useful tool in the prenatal diagnosis of congenital diaphragmatic hernias and eventrations. J Ultrasound Med 2009; 28:1365-1367
• Didier RA, DeBari SE, Oliver ER, et al. Secondary imaging findings aid in prenatal diagnosis and characterization of congenital diaphragmatic hernia. J Ultrasound Med 2019; 38: 1449-1456
• Jeanty C, Nien JK, Espinoza J, et al. Pleural and pericardial effusion: a potential ultrasonographic marker for the prenatal differential diagnosis between congenital diaphragmatic eventration and congenital diaphragmatic hernia. Ultrasound Obstet Gynecol 2007; 29: 378-387
• Minkner K, Alamo L. Pre- and neonatal imaging of gastrointestinal complications in congenital diaphragmatic hernia. Abdom Radiol 2018; 43: 574-582
• Oliver ER, DeBari SE, Adams SE, et al. Congenital diaphragmatic hernia sacs: prenatal imaging and associated postnatal outcomes. Pediatr Radiol. 2019; 49: 593-599
• Sohaey R and Zwiebel WJ. The fetal thorax: noncardiac chest anomalies. Semin. Ultrasound CT MR 1996; 17: 34-50
• Spaggiari E, Stirnemann J, Bernard JP, et al. Prognostic value of a hernia sac in congenital diaphragmatic hernia. Ultrasound Obstet Gynecol 2013; 41: 286-290

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