Congenital Diaphragmatic Hernia (CDH) Imaging

In patients presenting in the neonatal and infantile periods, the classic radiographic appearance of congenital diaphragmatic hernia is one in which the left hemithorax is filled with cystlike structures (loops of bowel), the mediastinum is shifted to the right, and the abdomen is relatively devoid of gas (see the images below). ^[11] In some cases, a few loops of intestine can be seen in the abdomen, but more often only the stomach remains visible within the abdomen.

Anteroposterior (AP) view of the chest in a patient with a congenital diaphragmatic hernia (CDH) shows herniation of bowel loops into the left hemithorax, with a shift of the heart and mediastinum to the right side.

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Anteroposterior (AP) view of the abdomen in a patient with a congenital diaphragmatic hernia (CDH) shows a gasless pattern caused by herniation of bowel loops into the right hemithorax.

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Interestingly, the stomach may be in an abnormal location, often more central than one would expect. The abnormal positioning of the stomach may be helpful in differentiating congenital diaphragmatic hernia from those few cases of congenital cystic adenomatoid malformation (CCAM) in which the cysts are large enough to mimic the air-filled intestinal loops. ^[11] In CCAM of the lungs, the stomach and bowel are normal in position and appearance.

Diagnostic considerations

If the chest radiograph is obtained before any air has entered the herniated bowel, diagnosing this condition with accuracy may be difficult. Similar difficulties arise when the liver alone is in the right hemithorax. In either case, the involved hemithorax is partially or totally opacified, and the mediastinal structures are shifted to the other side. In this circumstance, a large pleural fluid collection or mass may be present; however, in most such cases, air soon enters the intestine, and this finding establishes the diagnosis. In other cases, the condition may be diagnosed by noting abnormal intrathoracic positioning of a nasogastric tube. ^[11]

Unusual findings

Unusual findings include a contralateral pneumothorax, contralateral collapse/consolidation, fluid in the chest, and the absence of a contralateral aerated lung. ^[11] If herniation occurs on the right, the intestine and liver or the liver alone may fill the right hemithorax. If the liver is in the chest, its normal silhouette is not generally seen in the abdomen.

Morgagni hernias

Classically, Morgagni hernias appear as unilateral, mediastinal, and basal masses containing a variety of abdominal organs, including air-filled loops of intestine. Occasionally, these hernias may be bilateral, and in rare cases, they may produce significant respiratory distress. Large anterior-central diaphragmatic hernias may produce elevation of the cardiac silhouette and bilateral bulges to either side of the lower mediastinum. Often, these herniations occur into the pericardial cavity. When this occurs, serious cardiorespiratory compromise can result. ^{[3, 11]}

Postsurgical repair findings

After the repair of a congenital diaphragmatic hernia, an ipsilateral ex vacuo pneumothorax is a universal finding on all chest radiographs obtained immediately after surgery in neonates. This finding is unaffected by the use of a chest drain. ^[10]

The degree of expansion of the ipsilateral lung is variable. Final radiographs at discharge usually demonstrate a mild ipsilateral shift of the mediastinum. In most cases, this indicates increased pulmonary hypoplasia in the ipsilateral lung.

The postoperative radiographic course for patients presenting in later childhood is different. The ipsilateral lung is frequently fully expanded on the first postoperative radiograph, and the diaphragm usually occupies a normal position. These findings indicate a lesser degree of pulmonary hypoplasia. ^[10]

In adults with congenital diaphragmatic hernia, previously undiagnosed Bochdalek hernias are most frequently identified when patients undergo computed tomography (CT) scanning for reasons that appear to be unrelated to the hernia. These Bochdalek hernias usually contain retroperitoneal fat or a kidney. ^{[4, 18, 19]}

Some authors believe that, with the routine use of thin-section CT scanning on modern imaging equipment, the prevalence and characteristics of late-presenting Bochdalek hernia can be more accurately estimated ^{[19, 25]} ; however, small Bochdalek defects may occur in as many as 6% of older adults.

MRI can accurately depict congenital diaphragmatic hernia and permits an easy diagnosis. MRI findings can be used to differentiate this condition from other chest masses, and MRI is superior to ultrasonography in demonstrating the position of the fetal liver above or below the diaphragm. MRIs can clearly depict diaphragmatic discontinuity, a fetal compressed lung, and connecting bowel segments between the abdomen and chest. ^{[26, 5]}  

Most infants with congenital diaphragmatic hernia have at least 1 abnormality identified on MRI of the brain. In a study of 53 infants with congenital diaphragmatic hernia, 32 had at least 1 abnormality. The most common MRI findings were enlarged extra-axial spaces (36%), intraventricular hemorrhage (23%), ventriculomegaly (19%), white-matter injury (17%), and cerebellar hemorrhage (17%). The main predictors of brain injury were a requirement for extracorporeal membrane oxygenation, large diaphragmatic defect size, and lack of oral feeding at discharge. ^[27]

Pregnant women carrying a fetus with congenital diaphragmatic hernia are often referred for ultrasonography first because of suspected polyhydramnios. The definite ultrasonographic diagnosis of fetal congenital diaphragmatic hernia lies on the visualization of abdominal organs in the chest; the ultrasonographic hallmark of this condition is a fluid-filled mass just behind the left atrium and ventricle in the lower thorax, as seen on a transverse view.

In patients presenting in the prenatal period, ultrasonographic features indicative of congenital diaphragmatic hernia include polyhydramnios, an absent or intrathoracic stomach bubble, a mediastinal and cardiac shift away from the side of the herniation, a small fetal abdominal circumference, the absence of the stomach in the abdomen, and, rarely, fetal hydrops. ^{[15, 28, 29]}

Fetal cardiac ultrasonography can provide useful information for predicting the outcomes of isolated left-sided congenital diaphragmatic hernia. The ratio of the diameter of the tricuspid valve to that of the mitral valve (TV/MV ratio) has been found to be a reliable indicator of outcomes of isolated left-sided congenital diaphragmatic hernia. A TV/MV ratio greater than 1.72 has been found to discriminate nonsurvivors from survivors with better sensitivity and specificity. ^[30]

In a right-sided hernia, the right lobe of the liver alone may be herniated (see the image below), or associated hydrothorax and ascites may be observed. ^[15]

Fetal ultrasound markers of congenital diaphragmatic hernia severity have been found to be predictive of significant morbidity and death. Lung-to-head ratio less than 1, thoracic liver position, and aberrant stomach position have been found to be associated with delayed time to resolution of pulmonary hypertension and may be used to identify fetuses at high risk of persistent pulmonary hypertension. ^[29]

(See the image below.)

Ultrasonogram of a right-sided congenital diaphragmatic hernia shows the liver herniating through the defect.

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Romiti et al proposed a new CDH ultrasonographic marker in fetuses called the mediastinal shift angle. In their report, on the same ultrasound images commonly used for lung-to-head ratio (LHR) measurement, a landmark line was drawn from a point on the posterior face of the vertebral body, splitting it into 2 equal parts, to the midposterior surface of the sternum. Another landmark line was then traced from the same point of the vertebral body to touch tangentially the lateral wall of the right atrium. The angle between these 2 lines was used to quantify mediastinal shift and called the mediastinal shift angle (MSA). According to the researchers, statistical analysis confirmed an inverse correlation between MSA values and survival (P=.004), with the best cutoff value for MSA being 43.7°, which demonstrated the highest discriminatory power (sensitivity 63%; specificity 93.75%). ^[31]

Corsini et al reported that the pattern of lung ultrasound for CDH diagnosis in infants with respiratory distress includes partial absence of the hyperechoic line representing the normal diaphragmatic profile, partial absence of the pleural line in the affected hemithorax, absence of A lines in the affected area, presence of multi-layered area with hyperechoic contents in motion (normal gut), and possible presence of parenchymatous organs inside the thorax (ie, liver or spleen). ^[32]