DIAGNOSIS: Foramen of Morgagni hernia.

DISCUSSION

The diaphragmatic foramen of Morgagni hernia is located posterolateral to the sternum at the site of the internal mammary artery. The hernia usually occurs on the right side but may occur on the left or in the midline; it has also been described as retrosternal, parasternal, substernal, and subcostosternal (1). It is the least common diaphragmatic hernia and comprises only 3% of all surgically treated hernias (2).

First described by Giovanni Morgagni in 1761, the potential space for the hernia is produced by a congenital defect or weakened area that results from failure of the septum transversus of the diaphragm to fuse with the costal arches (1). This anatomic defect, best known as Morgagni's foramen, has also been referred to as Larrey's space (2). It is believed that the congenital foramen (weakened area) gradually stretches and that herniation through the foramen occurs later in life, possibly because of rapid changes in intra-abdominal pressure and aging of the diaphragm (1). Omental fat is freely moveable (3), and the most common contents of the hernia are omentum and transverse colon; however, the hernias have also been discovered to contain stomach, liver, cecum, terminal ileum, and ascending colon. The foramen of Morgagni hernia always has a peritoneal sac and is considered to be a direct-type hernia (4).

In adults, Morgagni hernias occur most often in overweight middle-aged women and are usually asymptomatic; however, patients may have abdominal or chest discomfort (as in the current case) or dyspnea. Although the hernia usually develops slowly, increased symptoms have been associated with weight lifting or other types of straining (2). Although considered to be a congenital abnormality (4), the foramen of Morgagni hernia is rarely diagnosed during the first years of life (1), and unlike other types of diaphragmatic hernias is only rarely associated with other congenital anomalies. Some evidence has been presented of a possible association between the hernia of Morgagni and trisomy 21 (5).

In radiographs, the foramen of Morgagni hernia appears as a homogenous mass in the right cardiophrenic angle (2). When the hernia contains bowel, the diagnosis can usually be made by radiographs and barium studies (6). CT is useful to determine that the paracardiac mass has fat density (2). The differential diagnosis of a fat density mass in the right cardiophrenic angle includes pericardial fat pad, lipoma, and a Morgagni hernia containing omentum. If the mass is not homogenous or contains material that has soft tissue density, diagnostic possibilities include liposarcoma, thymolipoma, and teratoma (6). Thin linear densities may be seen within the herniated omentum, and these are believed to be omental vessels. This finding helps differentiate a Morgagni hernia from a lipoma. CT is also helpful for demonstrating continuity between the fat density paracardiac mass and the abdominal fat (as in the present case). CT images reconstructed in the sagittal plane may show both continuity of the thoracic fatty mass with the omentum and the exact location of the diaphragmatic defect (3). In the current case, these findings are demonstrated in Figure 5. Magnetic resonance imaging has also been used successfully in establishing the diagnosis of foramen of Morgagni hernia because this modality establishes the fatty nature of the mass, identifies omental vessels, and demonstrates the defect in the diaphragm.

Surgical repair is usually indicated when symptoms increase in incidence or severity. It is important to determine the extent of the diaphragmatic defect and the contents of the hernia prior to surgery. Successful laparoscopic repair of these hernias has been reported (2).

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2. Gilkeson RC, Basile V, Sands MJ, Hsu JT. Chest case of the day. AJR Am J Roentgenol 1997;169:266-270.
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5. Honore LH, Torfs CP, Curry CJR. Possible association between the hernia of Morgagni and trisomy 21. Am J Med Genet 1993;47:255-256.
6. Sutro WH, King SJ. Computed tomography of Morgagni hernia [letter]. New York State Journal of Medicine 1987;September:520-521.