Describe the two types of hiatal hernia.

Sliding (axial) hiatal hernia: The gastroesophageal junction (B line) slides into the mediastinum above the diaphragm. 

Rolling (paraesophageal) hiatal hernia: The gastroesophageal junction is in a normal location, but the gastric fundus rolls into the mediastinum. The potential for infarction makes this type of hiatal hernia a surgical emergency.