The chest x-ray and CT scan abnormality in the right cardiophrenic angle most likely corresponds to: e) benign epicardial fat pad.

The prominent soft tissue focus in the right cardiophrenic angle is noted to have a fatty tissue density (negative Hounsefield units; –1 to –20 HU). Asymmetric deposition of fat within the thorax is not uncommon, most often seen in the epicardial space in the right cardiophrenic angle as in the case presented, or in the mid-lateral thoracic regions in a subpleural location, which can be mistaken on chest x-rays for peripheral lung lesions or sessile pleural plaques. A non-contrast CT scan of the thorax quickly and simply reveals the fatty nature of the tissue involved. These are incidental benign findings and no further follow-up is required.

A Morgagni hernia is a rare anterior congenital diaphragmatic hernia (CDH), which is also known as a retrosternal, or parasternal hernia. Accounting for only 2% of all CDH cases, it’s characterized by herniation through the foramina of Morgagni of which there is one on each side, located immediately adjacent to the xiphoid process of the sternum. These hernias almost always occur on the right side. This finding can be differentiated from a prominent epicardial fat pad by the presence of curvilinear densities coursing through the fat, representing omental blood vessels, which can be followed into the abdomen on the coronal CT reconstructed images. Most Morgagni hernias are asymptomatic but can cause respiratory distress in newborns if large enough.

Both an invasive primary bronchogenic carcinoma and pericardial adenopathy would exhibit soft tissue density (CT Hounsefield unit numbers around 35-60 HU). The carcinoma would likely be more irregular in outline, and the adenopathy would likely exhibit a more lobulated peripheral contour. A pericardial “spring water” cyst is a benign loculated fluid collection, which develops in the pericardial space, typically in the right cardiophrenic angle as well. Such a lesion would have a fluid CT density (0-30 HU). The negative HU value of the lesion presented (and similar appearance to nearby subcutaneous fat) confirms the presence of fat within.

 

References:

1. Minneci PC et al. Ann Thorac Surg 2004;77:1956-9.
2. Paling MR, Williamson BRJ. Radiology 1987;165:335-9.