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This year the 2018 meeting of the American Association of Clinical Anatomists is being held in Atlanta, GA., at the Grand Hyatt Buckhead Hotel and Conference Center. The program is full of interesting topics and is already a hit with all the attendees. Looking forward to the program.

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.

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

Images property of: CAA.Inc. 
Photographer: David M. Klein

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.

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:

• Esphageal hiatus

• Aortic hiatus

• Inferior vena cava hiatus

• Hiatuses (2) for the splanchnic nerves

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

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.

Images property of: CAA.Inc. Artist: Dr. E. Miranda

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.

The word acetabulum is formed by the combination of the Latin root [acetum], meaning "vinegar", and the Latin suffix [-abulum] a diminutive of [abrum], meaning a "cup", "holder", or "receptacle". Thus formed, the word acetabulum means "a small vinegar cup".

Roman soldiers liked to drink their water mixed with a small quantity of vinegar, so as to reduce the sensation of thirst. This mix was called "Posca". An acetabulum was used to add specific quantities of vinegar to the water, so over time the acetabula (plural form of acetabulum) were considered measuring devices. It is said that they measured one cup, or 2 1/2 oz. of wine.

The anatomical acetabula are bilateral cup-like depressions in the os coxae which serve as a component of the coxofemoral joint (hip joint). They are found at the intersection of the three bony components of the os coxae, the ilium, ischium, and pubic bone and look anteroinferiorly.

• Acetabular margin: An incomplete circular bony edge or border that marks the edge of the acetabulum

• Acetabular notch: The area where the acetabular margin is incomplete

• Acetabular labrum: Labrum (Lat. :lip). The acetabular labrum is a complete circular ring of fibrocartilage found on the acetabular margin that helps maintain the head of the femur in place. It is not shown in the accompanying image

• Lunate surface: A smooth, half-moon shaped area on the floor of the acetabulum. It is covered with hyaline cartilage and allows for articulation with the head of the femur

• Acetabular fossa: The non-articular region of the floor of the acetabulum. It contains fat, vessels, and the ligament of the head of the femur

Interesting fact:  You may find that in older English anatomy books the acetabulum is referred to as the cotyloid cavity. The word cotyloid arises from the Greek [κοτυλοειδές] and means "similar to a cup". This separation in terms still exists when studying anatomy in other languages. For example, in Spanish the acetabulum is called "cavidad cotiloídea" or "cotilo", and in French it is called "cavité cotyloïde" or "cotyle". I guess the Greek soldiers did not drink vinegar with their water...

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.

Click on the image for a larger version.

Thoracic anatomy, pathology and surgery, are some of the many lecture topics developed and presented by Clinical Anatomy Associates, Inc.

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