Ligaments of the Gastrointestinal Tract
Desmology is a subdivision of anatomy that focuses on the study of ligaments. It originates from the Greek word desmos, which means “bond”. A ligament is commonly defined as a fibrous connective tissue that is responsible for bonding bone to bone. However, the term is also used to describe peritoneal folds that anchor adjacent abdominal viscera to each other, or to the abdominal wall. The nomenclature associated with the ligaments of the digestive tract is based on the structures that they connect. For example, the hepatoduodenal ligament connects the liver to part of the duodenum. This article will focus on the ligaments associated with the gastrointestinal tract as well as any clinically significant point associated with the same.
By and large, the abdominal viscera are suspended in the abdominal cavity by peritoneal folds and ligaments. The liver, stomach, duodenum, and spleen are the gastrointestinal organs of focus that have attachments with each other as well as with the abdominal wall.
Coronary Ligament (Complex)
The liver is the largest accessory digestive organ within the peritoneal space. It has several ligamentous attachments that anchor the organ in the upper right quadrant of the abdominal cavity. The largest of the seven hepatic ligaments is the coronary ligament. This fibrous, double layered structure is a reflection of the diaphragmatic peritoneum that attaches to the posteroinferior aspect of the right lobe of the liver. The cranial layers of the coronal ligament further divide to anchor the superior surface of the liver to the inferior surface on the right hand side. Also on the right hand side, the caudal layers of the coronary ligament attach the inferior surface of the liver to the right kidney and its associated suprarenal gland. The attachment of the coronal ligament to the liver leaves a triangular area that is devoid of peritoneum that is referred to as the bare area of the liver. The coronary ligament of the right lobe of the liver is continuous with the right triangular ligament. However, there is no true coronary ligament on the left hand side. Instead the cranial and caudal layers of the coronary ligament approximate to form the left triangular ligament.
The triangular ligaments are asymmetrical bilateral structures that help to hold the liver in place. The right triangular ligament is a relatively short structure that is a continuation of the coronary ligament. It begins at the apex of the bare area of the liver.
The left triangular ligament is formed from the two layers of the coronary ligament. Consequently, the left triangular ligament projects over the cranial surface of the left lobe of the liver. The ligament lies anterior to the abdominal oesophagus, the medial part of the gastric fundus and the cranial segment of the lesser omentum. While the right triangular ligament is continuous with the coronary complex, the left coronary ligament is also continuous with both the falciform ligament and the lesser omentum. The arrangement is such that the posterior layer of the left triangular ligament is continuous with the lesser omentum inferolaterally, while the anterior layer of the left triangular ligament is continuous with the falciform ligament superomedially.
The second largest hepatic ligament is the falciform ligament. The sickled shaped ligament (as suggested by its name) takes a craniocaudal course along the anterior surface of the liver. Superiorly, the falciform ligament is attached to the anterior abdominal wall (just an inch to the right of median plane) and the inferior surface of the diaphragm. Inferiorly, it attaches to the superior surface of the liver between the left and right lobes. Like the other hepatic ligaments, the falciform ligament has two layers. The left leaf takes a lateral course to merge with the coronary ligament on the right, while the right leaf unites with the left triangular ligament medially. The inferior border of the falciform ligament has no hepatic attachments. Instead, it is occupied by the ligamentum teres hepatis (round ligament of the liver).
Ligamentum Teres Hepatis
During embryonic development, the left umbilical vein drains blood into the left portal vein. However, about two months postnatally, the vein degenerates and forms the ligamentum teres hepatis (Latin for the round ligament of the liver). The ligamentum teres hepatis continues in the inferior border of the falciform ligament and courses in the fissure of the ligamentum venosum on the inferior surface of the liver.
In utero, the ductus venosum was responsible for shunting blood from the left portal vein to the left hepatic vein, bypassing the hepatic circulation. During the first postnatal week, the ductus venosum degenerates and becomes the ligamentum venosum. This slender fibrous cord passes from the left branch of the portal vein upwards in the fossa bearing its name to reach inferior vena cava.
Hepatogastric and Hepatoduodenal Ligaments
The lesser omentum forms an “L” shaped attachment that extends from the distal segment of the abdominal oesophagus, along the lesser curvature of the stomach to the proximal part of pars superioris of the duodenum. It inserts on the inferior surface of the liver, adjacent to the fissure of the ligamentum venosum and the porta hepatis.
The lesser omentum may be further subdivided into the larger hepatogastric ligament and the smaller (but thicker) hepatoduodenal ligament. The two layers of the hepatogastric ligament are continuous with the posterior leaf of the left triangular ligament and the right coronary ligament. The later goes on to enclose the inferior vena cava. The hepatoduodenal ligament encircles the constituents of the porta hepatis (portal vein, bile duct and hepatic artery). The hepatoduodenal component of the lesser omentum forms the anterior border of the epiploic foramen of Winslow.
Ligament of Treitz
While the structure marking the transition from duodenum to the jejunum is often called the ligament of Treitz, it actually arises from the muscular bands of the right crus of the diaphragm. As a result, it is more aptly called the suspensory muscle of the duodenum. The muscle is a combination of fibromuscular fibers of smooth muscle (from pars horizontalis and pars ascendens of the duodenum) and skeletal muscle (from the diaphragm). It has a relatively convoluted course around the oesophagus, roots of the celiac trunk and superior mesenteric arteries before inserting in the duodenojejunal flexure of the small intestines. Contraction of the muscle causes distention at the duodenojejunal flexure, which promotes gastric motility.
Like the lesser omentum, the greater omentum has its origins from the stomach. However, the greater omentum originates from the greater curvature of the stomach. The structure can be described as a double layered sheet, with the posterior sheet recurring to insert along the transverse colon. The segment of the greater omentum that inserts at the root of the transverse mesocolon is known as the gastrocolic ligament or gastrocolic omentum. It forms the anterior boundary of the lesser sac of the abdomen.
Gastrosplenic (Gastrolienal) Ligament
A portion of the greater omentum also leaves the greater curvature of the stomach and attaches to the spleen. This is known as the gastrosplenic or gastrolienal ligament. The two layers of the gastrosplenic ligament divide at the hilum of the spleen and envelopes the organ. The layers subsequently re-join to form the lienorenal ligament, which attaches the spleen to the left kidney. For completion, it is important to note that another ligamentous structure known as the left colic (splenic) flexure connects the spleen to the diaphragm.