Clinical case: Giant inguinal hernia

Objectives

• Why morbid obesity is associated with respiratory distress.
• The difference between an indirect and a direct inguinal hernia.
• What is megacolon and how does it sometimes contribute to the development of inguinal hernias.
• The underlying basis of the appearance of structures of differing radiological densities on a CT image. The explanation should include whether these identical densities are relevant to other imaging modalities such as radiography, MRI and ultrasound.

Association between morbid obesity and respiratory distress

Morbid obesity is associated with a reduction in lung volume as body fat occupies an increasing percentage of body cavities. Further, as illustrated in Figure 3, excess intra-abdominal fat causes elevation of the diaphragm and restricts its movements during respiration. The cause of death in this patient is not clearly identified in the case description but there is no doubt that respiratory difficulties contributed to it.

Differences between indirect and direct inguinal hernias

This patient’s scrotum was massively distended due to the presence in the scrotum of herniated abdominal fat, fluid and viscera (Figure 3). In an indirect inguinal hernia, the spermatic cord and inguinal canal form a passageway allowing the abdominal contents to herniate out of the abdominal cavity and pass into the scrotum (Figure 4). The sac of an indirect inguinal hernia emerges from the abdominal cavity lateral to the inferior epigastric artery.

In a direct inguinal hernia, the herniated material emerges from the abdominal cavity directly through the abdominal wall, often passing through the superficial inguinal ring, but it does not pass through the deep inguinal ring.

A direct inguinal hernia can also enter the scrotum but it passes medial to the inferior epigastric artery as it exits the abdominal cavity. In the case described here, the surgeon was able to confirm that both right and left GIH’s were indirect hernias by their relationship to the inferior epigastric artery.

Contributions of a megacolon to the development of inguinal hernias

Megacolon (Figure 5) refers to extreme dilation of the colon (large bowel). It has multiple causes (congenital and acquired) and is associated with chronic constipation. Although this patient did not have megacolon, in some patients megacolon can contribute to the development of GIH because of the chronic straining that occurs during bowel movements.

Radiological densities in CT images

CT imaging is based on x-ray technology and thus the apparent density (typically represented by “whiteness”) of a structure on a CT image is based on the physical nature of the structure’s molecule’s ability to scatter x-ray photons. Thus, bone is radiographically dense and its molecules scatter more photons than fat. In plain radiography and CT, metal and contrast material provides the brightest white image, followed by bone and calcification. The darkest images come from air, followed by adipose tissue and soft tissues.

The radiographic density of a structure is not transferable to ultrasound or MRI. In ultrasound, bright (hyperechoic) structures are more reflective of sound waves than dark (hypoechoic) structures. In MRI, the intensity (typically brightness) of a structure is dependent on the state of its hydrogen atoms and on the specific magnetic sequence used to produce that particular image.