Esophageal hiatus hernia in situ.
The arrow points to stomach and greater
omentum herniating into the thorax

UPDATED: An esophageal hiatus hernia (also known as a hiatal hernia) is caused by a dilation of the esophageal hiatus and its component structures, the phrenoesophageal membranes (ligaments).

Since the intraabdominal pressure is higher than the intrathoracic pressure, abdominal contents -usually stomach and greater omentum- can herniate through the dilated esophageal hiatus into the mediastinum, the central region of the thoracic cavity. This presents as a hernia sac whose walls are formed by endothoracic fascia, phrenoesophageal membranes and parietal peritoneum. 

There are two main types of esophageal hiatus hernias. Type I is known as a "sliding hiatal hernia" and is characterized by a complete ascension of the esophagogastric junction and abdominal esophagus into the thoracic hernia sac. This is usually accompanied by a typical "hourglass image" in a radiographic assessment, and also presents with gastroesophageal reflux disease (GERD). Type I esophageal hiatus hernias are more common.

Esophageal hiatus hernia, reduced.
The dotted line shows the edge of
the enlarged esophageal hiatus

Type II esophageal hiatus hernia is known as a "paraesophageal hernia" and represent about 5 - 15% of esophageal hiatus hernias. In this case, the esophagogastric junction maintains its anatomical position inferior to the respiratory diaphragm, but the fundus and body of the stomach, along with some greater omentum herniate alongside the esophagus into the mediastinal region of the thoracic cavity. Although there can be GERD, this type of hernia usually presents with little symptomatology, and when it does, symptoms are related to ischemia or partial to complete obstruction. There are variations of type II hernia, which are classified as Type III and IV. Type IV, although rare, will include other viscera in the hernia sac, including colon, spleen, or even small intestine.

The accompanying images above depict a Type I esophageal hiatus hernia. The superior image shows the hernia in situ where the stomach and greater omentum are still in the hernia sac. The inferior image shows the contents reduced and the abdominal esophagus being pulled into the abdominal cavity. The dotted line shows the dilated esophageal hiatus that needs to be repaired to prevent recurrence of the pathology.

Click on this link for additional information on esophageal hiatus hernia surgery.

The image below answers a question by Victoria Guy Ratcliffe, who asked via Facebook "What would it be if it feels like you've got a blockage right at the level of the heart? That's too high for a hiatal hernia, isn't it?" The image answers the question. It shows a dissection of the left side of the thorax. The anterior thoracic wall and the left lung have been removed. The heart is immediately superior and anterior to the esophageal hiatus, and the hernia sac of a Type I esophageal hiatus hernia is seen immediately posterior and in contact with the heart. Whether this means that you will "feel" the hernia, it is up for debate, as all these structures have visceral innervation. Most probably, a well-developed Type II esophageal hiatus hernia might interfere with swallowing at this level, causing the sensation she mentions. Thanks for the question, Tori.

For additional information:
"Approaches to the Diagnosis and Grading of Hiatal Hernia" Kahrilas et al Best Pract Res Clin Gastroenterol. 2008 ; 22(4): 601–616.

Respiratory diaphragm

The term [hiatus] derives from the Latin word [hiare], meaning to "gape" or to "yawn". In human anatomy this term is used to mean an "opening" or a "defect". It must be pointed out that in anatomy (and surgery) the term "defect" does not necessarily mean "defective". In most cases a "defect" is a normal opening in a structure, such as the esophageal hiatus. The plural form is either [hiatus] or [hiatuses].

In the case of the respiratory diaphragm, there are seven such openings, seven normal hiatuses. On top of this, you can find an abnormal opening caused by incomplete congenital closure of the dome of the diaphragm, a congenital diaphragmatic hernia (CDH), also known as Bochdalek's hernia, found in the posterior aspect of the respiratory diaphragm.

The seven hiatuses of the respiratory diaphragm are:

• Esophageal hiatus

• Aortic hiatus

• Inferior vena cava hiatus

• Hiatuses (2) for the superior epigastric vessels, which are the inferior continuation of the internal thoracic (mammary) vessels. Also known as the hiatuses of Morgagni. A hernia in a newborn through this hiatus is also considered a CDH.

• Hiatuses (2) for the splanchnic nerves

Based on the above it is wrong (maybe not wrong, but incomplete) to say that a patient has a "hiatal hernia", as the term does not include which hiatus is involved. In fact the hernia of Morgagni is also a "hiatal hernia" as the hernia passes through a normal defect in the respiratory diaphragm. Come to think of it, it could also be a hernia in a hiatus somewhere else in the body, such as a hernia of Schwalbe, a type or pelvic diaphragm hernia.

Note: Thanks to DHREAMS of the Columbia University Medical Center for the link on CDH.

Sources:
1. "The Origin of Medical Terms" Skinner, HA 1970 Hafner Publishing Co.
2. "Medical Meanings - A Glossary of Word Origins" Haubrich, WD. ACP Philadelphia
3 "Tratado de Anatomia Humana" Testut et Latarjet 8 Ed. 1931 Salvat Editores, Spain
4. "Anatomy of the Human Body" Henry Gray 1918. Philadelphia: Lea & Febiger Image modified by CAA, Inc. Original image by Henry Vandyke Carter, MD., courtesy of bartleby.com

Esophagogastric junction

UPDATED:  The esophageal hiatus is one of the seven hiatuses found in the respiratory diaphragm allowing passage of structures between the thorax and abdomen. As it name implies, the esophageal hiatus is the passageway for the esophagus. It also allows passage of the anterior and posterior vagus nerves, (CN X).

The hiatus is bound by two muscular crura, both of which arise from the right tendinous aortic crus. Since the intraabdominal pressure is higher than the intrathoracic pressure, there is a series of structures at the phrenoesophagogastric junction to close the esophageal hiatus.

The infradiaphragmatic parietal peritoneum reflects off the diaphragm towards the stomach to form its serosa layer (visceral peritoneum). At the same time the infradiaphragmatic fascia, also known as the  endoabdominopelvic fascia, splits into two components or limbs. These are the superior and inferior phrenoesophageal ligaments or phrenoesophageal membranes. (the root [-phren-] means "diaphragm"). These phrenoesophageal ligaments create a disc-like plug between the abdomen and the thorax. This "plug" is reinforced by a circular infradiaphragmatic fat pad. The phrenoesophageal ligaments are reinforced on their thoracic aspect by the endothoracic fascia.

The lower esophagus has a dilation (evident in the image) called the "esophageal ampulla", in relation to this dilation the circular muscle layer of the esophagus slightly thickens creating the so-called "lower esophageal sphincter". This area is not a true anatomical sphincter, but rather is a functional sphincter. 

The esophagogastric mucosal junction shows a marked transition in the shape of a wavy line. This is called the Z-line or the ora serrata. Extensions of the gastric mucosa and submucosa inferior to the ora serrata create a valve-like flap called the "gastroesophageal flap valve". When viewing this mucosal flap through and endoscope, it looks corrugated and flower-like, hence it is also called the "rosette". 

The congenital or pathological dilation of the esophageal hiatus can predispose to esophageal hiatus hernia.

Sources:
1 "Tratado de Anatomia Humana" Testut et Latarjet 8 Ed. 1931 Salvat Editores, Spain
2. "Anatomy of the Human Body" Henry Gray 1918. Philadelphia: Lea & Febiger
Original image by Dr. E. Miranda

Esophagogastric junction

The esophagogastric junction is a complex anatomical region found at the esophageal hiatus of the  respiratory diaphragm. It allows passage of he esophagus from the thorax into the abdomen.

The hiatus is bound by two muscular crura, both of which arise from the right tendinous aortic crus. Since the intraabdominal pressure is higher than the intrathoracic pressure, there is a series of structures at the phrenoesophagogastric junction to close the esophageal hiatus.

The infradiaphragmatic parietal peritoneum reflects off the diaphragm towards the stomach to form its serosa layer (visceral peritoneum). At the same time the infradiaphragmatic fascia, also known as the  endoabdominopelvic fascia, splits into two components or limbs. These are the superior and inferior phrenoesophageal ligaments or phrenoesophageal membranes. (the root [-phren-] means "diaphragm"). These phrenoesophageal ligaments create a disc-like plug between the abdomen and the thorax. This "plug" is reinforced by a circular infradiaphragmatic fat pad. The phrenoesophageal ligaments are reinforced on their thoracic aspect by the endothoracic fascia.

The lower esophagus has a dilation (evident in the image) called the "esophageal ampulla", in relation to this dilation the circular muscle layer of the esophagus slightly thickens creating the so-called "lower esophageal sphincter". This area is not a true anatomical sphincter, but rather is a functional sphincter. 

The esophagogastric mucosal junction shows a marked transition in the shape of a wavy line. This is called the Z-line or the ora serrata. Extensions of the gastric mucosa and submucosa inferior to the ora serrata create a valve-like flap called the "gastroesophageal flap valve". When viewing this mucosal flap through and endoscope, it looks corrugated and flower-like, hence it is also called the "rosette". 

The congenital or pathological dilation of the esophageal hiatus can predispose to esophageal hiatus hernia.

Sources:
1 "Tratado de Anatomia Humana" Testut et Latarjet 8 Ed. 1931 Salvat Editores, Spain
2. "Anatomy of the Human Body" Henry Gray 1918. Philadelphia: Lea & Febiger
Original image by Dr. E. Miranda

Sternum, anterior view

UPDATED:The sternal angle is the term used to denote the angulation at the  joint between the manubrium and the body of the sternum. This transverse joint is called the "manubriosternal joint" and is a secondary cartilaginous joint of a type known as a symphysis. The angle varies between 160 and 169 degrees.

It is know eponymously as the "angle of Louis" named after Antoine Louis¹ (1723-1792), a French physician. The importance of the sternal angle is that of an anatomical superficial landmark, which forms a horizontal plane which indicates a series of anatomical occurrences, as follows:

• Location of the cartilages of the second rib
• Beginning and end of the aortic arch
• Boundary between the inferior and superior mediastinum
• Location of the bifurcation of the trachea
• Posteriorly, the plane of the sternal angle passes trough the T4-T5 intervertebral disc (sometimes a little lower, through the superior aspect of T5)
• Highest point of the pericardial sac.
• It is the point where the right and left pleurae meet in the midline. They touch, but their pleural spaces do not communicate (usually).

1. Some authors contest the eponym, adjudicating it to Pierre Charles Alexander Louis (1787-1872), another French physician.
Image property of: CAA.Inc.. Artist: David M. Klein

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