Understanding Hiatal Hernia and Its Types

It can be unsettling to learn about a hiatal hernia (also called a hiatus hernia) for the first time, especially if it was discovered “by accident” while your doctor was looking for something else ^[1]. Whether you have dealt with years of reflux or were completely unaware of any issue, finding out your anatomy has shifted is a significant moment.

Biologically, a hiatal hernia occurs when the opening in your diaphragm (the large muscle separating your chest from your abdomen) becomes enlarged or weakened ^[2]. This opening is called the esophageal hiatus. Normally, it acts like a snug portal around your esophagus, helping to keep your stomach where it belongs ^[3]. When this opening widens, a portion of your stomach—and sometimes other organs—can slide or bulge upward into your chest cavity ^[4].

The Anatomy of the Hiatus

Your body relies on a specialized “gatekeeper” system to keep stomach acid down. This system is made of two parts: the lower esophageal sphincter (a ring of muscle at the bottom of your food pipe) and the crural diaphragm (the muscle of the hiatus itself) ^[3][5]. In a healthy body, these two muscles line up perfectly to create a strong barrier.

In a hiatal hernia, this barrier is disrupted. As the hiatus widens, the two muscles can become separated. Doctors often use a test called high-resolution manometry to measure this gap; a separation of more than 2 centimeters is a suggestive finding of a hernia that must be interpreted alongside the complete report and other imaging ^[6][7].

Understanding the Four Types

Doctors categorize hiatal hernias into four types based on what has moved and where the “junction” (the point where your esophagus meets your stomach) is located.

• Type I: Sliding Hiatal Hernia
  This is the most common form, accounting for the vast majority of cases ^[8]. In a sliding hernia, the junction between your esophagus and stomach slides up through the hiatus into your chest ^[9]. It may slide back and forth depending on your posture or the pressure in your belly. Type I hernias are strongly associated with acid reflux, though they do not automatically cause it in everyone.
• Type II: Paraesophageal Hernia
  This is much rarer. In a true Type II hernia, the junction stays in its correct place below the diaphragm, but the top part of the stomach (the fundus) pokes through the opening alongside the esophagus ^[10]. Some modern research suggests this type is so rare that many cases labeled “Type II” are actually a different anatomical variation called a parahiatal hernia ^[11]. Classification can vary between radiologists and surgeons, and your management depends on your actual anatomy and symptoms, not the label alone.
• Type III: Mixed Hernia
  As the name suggests, this is a combination of Types I and II. Both the junction and the top of the stomach have moved up into the chest ^[9]. These are often larger than Type I hernias.
• Type IV: Complex Hernia
  This is the most advanced type. In a Type IV hernia, the opening is large enough that other abdominal organs—such as the colon, spleen, pancreas, or small intestine—have also migrated into the chest cavity along with the stomach ^[12][13].

Why Hernias Are Often “Hidden”

It is very common for a hiatal hernia to be found incidentally. Because the symptoms can be vague or non-existent, many people live with them for years without knowing.

The likelihood of having a hiatal hernia increases significantly as you age. In one study of older adults, the number of people with a hernia rose from about 2% in their 50s to over 16% by their 80s ^[1]. In some medical groups, such as patients seeking weight-loss surgery, nearly half of patients over the age of 60 were found to have a hernia ^[14].

Body weight also plays a role. Increased intra-abdominal pressure—the pressure inside your belly—can physically push the stomach upward through the hiatus ^[2]. Studies have shown that a higher Body Mass Index (BMI) or a larger waist circumference is often linked to a larger hiatal opening ^[15][1]. Because this process happens slowly over many years, your body may “adjust” to the change, which is why your doctor might only spot it during a routine CT scan or an endoscopy for an unrelated concern ^[16][17].