Anatomic and Normal Radiologic Features

The key to understanding the significance of the duo-denocolic relationships is the insertion of the root of the transverse mesocolon and its planes of reflection (Fig. 10-1).

The hepatic flexure of the colon is characteristically composed of two curvatures.2 The proximal, more posterior one continues from the fixed extraperitoneal ascending colon and is related to the inferior and lateral edge of the right kidney and the posterolateral tip of the liver. The colon then passes immediately anteromedially over the descending duodenum to the second curve of the hepatic flexure, which is more anterior and is related above to the gallbladder.

At a point between the two curvatures of the hepatic flexure, as the colon is in intimate relationship to the descending duodenum (Fig. 10-2), it begins to pick up the peritoneal sling of the transverse mesocolon. The colon in this area is then in virtual contiguity with the second portion of the duodenum, with the very short edge of the beginning reflection of the transverse mesocolon providing a mesenteric plane (Figs. 10-3 and 10-4).

The root of the transverse mesocolon broadly intersects the infraampullary portion of the descending duodenum and then continues along the anterior surface of the pancreas. Here it is attached to the midportion of the head and the inferior surface of the body and tail. The nonperitonealized bare area, wide on the right and progressively thinner toward the left, thus provides a shared anatomic plane, between the pancreas and descending duodenum behind and the transverse colon in front, along the leaves of the transverse mesocolon.

The transverse mesocolon itself is a fan-shaped structure in the horizontal plane of the body. Short at its beginning, it is longest in the midsagittal plane, becom-

Transverse Mesocolon

Fig. 10—1. The root of the transverse mesocolon.

It extends across the infraampullary portion of the duodenum and lower border of the pancreas. Note the relationships of the anterior hepatic flexure of the colon (AF) and of the duodenojejunal junction. PF = posterior hepatic flexure. MP marks the location of Morison's pouch, the intraperitoneal posterior extension of the right subhepatic space anterior to the right kidney. (Reproduced from Meyers and Whalen.1)

Fig. 10—1. The root of the transverse mesocolon.

It extends across the infraampullary portion of the duodenum and lower border of the pancreas. Note the relationships of the anterior hepatic flexure of the colon (AF) and of the duodenojejunal junction. PF = posterior hepatic flexure. MP marks the location of Morison's pouch, the intraperitoneal posterior extension of the right subhepatic space anterior to the right kidney. (Reproduced from Meyers and Whalen.1)

Morison Pouch

Fig. 10-2. A normal upper GI series frequently shows lateral pressure on the descending duodenum from a feces-distended anterior hepatic flexure of the colon. This reflects their contiguous anatomic relationship.

Fig. 10—3. Transverse section through the right abdomen at the level of the duodenal bulb (DB) and the proximal descending duodenum (DD).

Note the intimate relationship of the hepatic flexure of the colon (C) at the beginning reflection of the transverse mesocolon. S = stomach; Gb = gallbladder; L = liver; K = kidney.

(Reproduced from Meyers and Whalen.1)

Relation Descending Colon

Fig. 10—4. Right parasagittal section at the level of the duodenal bulb (DB) and the decending duodenum

(DD), showing their relationship to the anterior hepatic flexure (AF) of the colon before it continues ventrally as the transverse colon (TC). The dashed line indicates the transverse mesocolon. (Reproduced from Meyers and Whalen. )

ing abbreviated laterally once again as the colon comes into relationship to the left kidney and the spleen. The length of the transverse mesocolon varies. It tends to be short in stocky individuals and long in tall, thin individuals.

The retroperitoneal duodenum bends forward after its ascending portion at the level of the ligament of Treitz to penetrate the posterior parietal peritoneum and continue as the intraperitoneal jejunum.

Although usage of the term ligament of Treitz for the duodenojejunal function is widely employed, it is not only inaccurate but may be misleading.3 The duodenojejunal flexure is generally about 2.5 cm left of the midline at the level of the inferior border of the first lumbar vertebra.4 In 1853, Treitz5 (Fig. 10-5) described the suspensory muscle of the duodenum as a thin triangular band ascending behind the pancreas to blend with the dense connective tissue around the stems of the superior mesenteric artery and celiac axis.6 It is a curious fact that anatomists refer to the structure as the suspensory muscle of the duodenum, whereas clinicians refer to it as the ligament of Treitz. It is generally conceived of and illustrated in anatomic atlases as a thin fibromus-cular band limited to the duodenojejunal junction. Yet, exclusive attachment to the flexure is rare. Rather, the muscle is usually attached to the third and fourth portions of the duodenum and frequently to the duode nojejunal flexure as well (Fig. 10-6). At its base, the smooth muscle fibers of the suspensory muscle are continuous with the longitudinal and circular muscle fibers of the duodenum. Superiorly, the muscle is gradually replaced by collagenous and elastic fibers. Its overall length varies from 1.25-6.4 cm. The fibromuscular structure plays an important role in the embryologic rotation of the bowel and in facilitating normal progression of contents from the extraperitoneal duodenum to the mesenteric small bowel and contributes to the effects of the superior mesenteric artery syndrome.3,8

The duodenojejunal junction is in intimate relationship to the inferior reflection of the transverse meso-colon (Figs. 10-1 and 10-7). It also serves as a useful landmark for dividing the body and tail of the pancreas.

The duodenojejunal junction, fixed by the ligament of Treitz, generally maintains its position throughout life. The duodenal bulb and proximal portion of the second duodenum, however, tend to descend with age, with progressive laxity of support, a change most marked in the fifth and sixth decades.9 Nevertheless, the position of the root of the transverse mesocolon, which separates the peritoneal cavity from the lesser sac, can be constantly indicated on an upper GI series by a line drawn from the infraampullary segment of the descending duodenum to a point immediately above the duodenoje-junal junction. This delimits the most superior ascent of

Ligament Treitz

Fig. 10-5. Vaclav (Wenzel) Treitz (1819-1872), age 41.

Treitz was a Bohemian-born pathoanatoinist who held faculty positions in Vienna, Krakow, and Prague. In 1853, he described "A new muscle in the human duodenum, over elastic sinews and some other anatomical relations," now generally referred to as the ligament of Treitz. In 1857 in an article entitled "Hernia Retroperitonealis: A Contribution to the History of the Internal Hernias," he discussed the anatomic relationships at the site of the passage of the duodenum into the jejunum bordered by the inferior mesenteric vein and left colic artery, also called the vascular arch of Treitz.

(Courtesy of the Institut für Geschichte der Medizin der Universität Wien, Museum Josephinum, Vienna.)

Ligament Treitz Separates

Fig. 10—6. Variations of the attachment of the suspensory muscle of the duodenum (ligament of Treitz).

(a) Attachment to the third and fourth portions of the duodenum and the duodenojejunal flexure. This occurs in 40-61% of cases.

(b) Multiple, separate divisions are not unusual.

(c) Attachment to the third and fourth positions of the duodenum only. This occurs in 31-53% of cases.

(d) Attachment to the duodenojejunal flexure only. This occurs in 0-8% of cases. (Reproduced from Akin et al.7)

Fig. 10—6. Variations of the attachment of the suspensory muscle of the duodenum (ligament of Treitz).

(a) Attachment to the third and fourth portions of the duodenum and the duodenojejunal flexure. This occurs in 40-61% of cases.

(b) Multiple, separate divisions are not unusual.

(c) Attachment to the third and fourth positions of the duodenum only. This occurs in 31-53% of cases.

(d) Attachment to the duodenojejunal flexure only. This occurs in 0-8% of cases. (Reproduced from Akin et al.7)

Suspensory Muscle The Duodenum

Fig. 10—7. Left parasagittal section at a level lateral to the duodenojejunal junction.

Shown are the relationships of the proximal jejunal loops (JL) to the transverse colon (TC) and its mesocolon (arrowheads), coursing along the inferior aspect of the tail of the pancreas (P). The section is also through the spleen (Sp) and the left kidney (LK). (Reproduced from Meyers and Whalen.1)

Fig. 10—7. Left parasagittal section at a level lateral to the duodenojejunal junction.

Shown are the relationships of the proximal jejunal loops (JL) to the transverse colon (TC) and its mesocolon (arrowheads), coursing along the inferior aspect of the tail of the pancreas (P). The section is also through the spleen (Sp) and the left kidney (LK). (Reproduced from Meyers and Whalen.1)

small bowel loops posterior to the transverse colon normally possible (Fig. 10-8).

On the right, the colon inferiorly and the descending duodenum medially provide two of the boundaries of the posterior extension of the subhepatic space (Mori-son's pouch) anterior to the kidney (Fig. 10-1).

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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