Bochdalek hernia is the most common form of diaphragmatic hernia. Gale reported an incidence of 6 per cent in 940 adults who had chest and abdominal CT examinations. Bochdalek hernia may occur if there is delayed or incomplete closure of the embryonic pleuroperitoneal membrane during the seventh week of gestation. These hernias are seen far more commonly on the left than on the right. The size of defect varies widely. A small defect may contain only retroperitoneal fat, a portion of the spleen or kidney, or omentum. When large, almost the entire abdominal contents may be in the hemithorax. Large Bochdalek hernias are a rare cause of severe acute respiratory distress in neonates needing urgent surgical correction. The initial chest radiograph reveals the fluid-filled loops of bowel presenting as a water density cystic mass within the hemithorax, with varying degree of contralateral mediastinal shift. In the adult, Bochdalek hernia can present as a soft tissue mass adjacent to the posteromedial aspect of a hemidiaphragm on the chest radiography. CT scans or MR imaging can easily demonstrate the diaphragmatic defect and the hernia contents (Fig 1). Occasionally, spiral CT with sagittal or coronal reformation may be required to demonstrate small diaphragmatic defects (Fig 2). Hypogenetic lung syndrome may have associated anomaly such as Bochdalek hernia involving the right hemidiaphragm (Fig 3).
Fig 1: BOCHDALEK HERNIA
A 64-year-old asymptomatic woman. A. Routine chest radiograph: round regular mass in the retrocardiac area. B. CT scan: Small defect of the left diaphragm (arrow). C. Coronal T1-weighted MRI: herniated retroperitoneal fat through the diaphragmatic defect.
Fig 2: SMALL BOCHDALEK HERNIA
Follow-up CT scan after chemotherapy for bronchogenic carcinoma of the right upper lobe in a 68-year-old man. A. contrast-enhanced CT scan: fat-containing small nodule in the left lower lobe completely surrounded by pulmonary parenchyma, initially mistaken for metastasis at the pulmonary window setting. Also note hepatic metastases. B. CT scan at the lower level: small discontinuity in the left diaphragm. C. CT scan with sagittal reformation: mushrooming in the diaphragmatic contour by the herniated retroperitoneal fat.
Fig 3: HYPOGENETIC LUNG SYNDROME
Right paracardiac mass incidentally discovered on routine chest radiography in an asymptomatic 45-year-old man. A. Chest radiograph: small right lung with anomalous venous return (small arrows) and round regular opacity in the right lower hemithorax (arrows) suggestive of pulmonary sequestration. B. CT scan with pulmonary window setting: anomalous venous return of right inferior pulmonary vein (arrows) to the inferior vena cava. C. Contrast-enhanced CT scan: a portion of liver herniated into the chest (arrow). D. Coronal contrast-enhanced MRI: Bochdalek hernia with herniated liver and anomalous venous return (arrow). E. MRI angiography: anomalous venous return (white arrows)and Budd-Chiari syndrome (arrows) due to liver hernia compressing hepatic veins.