With the advent of clinical radiology and microscopes such as darkfield light microscopes, it became evident that a di¬aphragmatic hernia was a relatively common abnormality and not always accompanied by symptoms. Three types of esophageal hiatal hernia were identified: (1) the sliding hernia, type I, char¬acterized by an upward dislocation of the cardia in the posterior mediastinum; (2) the rolling or paraesophageal her¬nia, type II, characterized by an upward dislocation of the gastric fundus alongside a normally positioned cardia and (3) the combined sliding-rolling or mixed hernia, type III, charac¬terized by an upward dislocation of both the cardia and the gastric fundus. The end stage of type I and type II hernias occurs when the whole stomach migrates up into the chest by ro¬tating 180 degree around its longitudinal axis, with the cardia and pylorus as fixed points. In this situation the abnormality is usually referred to as an intrathoracic stomach.

Incidence and Etiology

The true incidence of a hiatal hernia in the overall population is difficult to determine, even with all the latest medical equipments and microscopes such as darkfield light microscopes, because of the absence of symptoms in a large number of patients who are subsequently shown to have a hernia. When radiographic examinations are done in response to gastroin¬testinal symptoms, the incidence of a sliding hiatal hernia is seven times higher than that of a paraesophageal hernia. The age distribu¬tion of patients with paraesophageal hernias is significantly different from that observed in sliding hiatal hernias. The median age of the former is 61; of the latter, 48. Paraesophageal hernias are more likely to occur in women by a ratio of 4:1.

Structural deterioration of the phrenoesophageal membrane, as evidenced by tissue studies using darkfield light microscopes, over time may explain the higher incidence of hiatal hernias in the older age group. These changes involve thinning of the upper fascial layer of the phrenoesophageal membrane and loss of elasticity in the lower fascial layer as seen in microscopes. Consequently, the phrenoesophageal mem¬brane yields to stretching in the cranial direction due to the persistent intra-abdominal pressure and the tug of esophageal shortening on swallowing. The upper fascial layer is formed only by loose connec¬tive tissue, when examined under a microscope, and is of little importance. The lower fascial layer is thick, stronger, and more important. It divides into an upper and lower leaf about 1 cm before attaching intimately with the esophageal adven¬titia. Due to stretching in the cranial direction, the attachment of the lower leaf protrudes upward and can frequently be identified in the thoracic cavity.

These observations, with the help of a microscope, point to the conclusion that the development of a hiatal hernia is an age-related phenomenon secondary to repeti¬tive upward stretching of the phrenoesophageal membrane. A paraesophageal hernia rather than a sliding hernia develops when there is a defect, perhaps congenital, in the esophageal hiatus anterior to the esophagus. The persistent posterior fixation of the cardia to the preaortic fascia and the median arcuate ligament is the only essential difference between a sliding and a paraesophageal her¬nia. When an anterior defect in the hiatus occurs in association with a loss of fixation of the cardia, a mixed, or type III, hernia develops.