Anatomic Considerations

Virtually all of the pancreas is an extraperitoneal organ. However, a nonperitonealized bare area results from the reflections of the posterior parietal peritoneum to form the two leaves of the transverse mesocolon.7 This extends across the lower border of the organ anteriorly (Fig. 11-1). On the right, the transverse mesocolon begins at the point where the anterior hepatic flexure of the colon immediately crosses ventral to the second portion of the duodenum. The bare area then extends as a broad strip across the infraampullary portion of the descending duodenum and continues across the head, body, and tail of the pancreas. The ascending colon and the proximal, more posterior hepatic flexure are completely extraperitoneal.

Significantly, the tail of the pancreas, after extending across the left kidney, is actually intraperitoneal in that it is incorporated or ensheathed within the leaves of the splenorenal ligament. By definition, any structure within a mesenteric attachment is intraperitoneal. Anatomic continuity is established by the peritoneal reflections constituting the supporting ligaments of the left upper quadrant. Figures 11-2 and 11-3 show the relationships of the tail of the pancreas within the spleno-renal ligament to the transverse mesocolon, phrenico-

Fig. 11—1. Mesenteric relationships of the pancreas.

Frontal drawing shows the relationships of the transverse mesocolon (TM) and its continuity with the small bowel mesentery (SBM), splenorenal ligament (SRL), and phrenicocolic ligament (PCL). (Reproduced from Meyers and Evans.2)

Fig. 11—1. Mesenteric relationships of the pancreas.

Frontal drawing shows the relationships of the transverse mesocolon (TM) and its continuity with the small bowel mesentery (SBM), splenorenal ligament (SRL), and phrenicocolic ligament (PCL). (Reproduced from Meyers and Evans.2)

colic ligament, and the peritoneal reflections of the descending colon. The phrenicocolic ligament8 is attached to the anatomic splenic flexure of the colon at the omental and mesocolic taeniae.9 It represents the most lateral continuity of the transverse mesocolon and splenorenal ligament and thereby marks the site of transition from the intraperitoneal transverse colon to the extraperitoneal descending colon.

Of further clinical significance is the fact that the root of the small bowel mesentery, at its origin near the inferior portion of the pancreas, is anatomically continuous with that of the transverse mesocolon (Fig. 11-1). At this point, it is in relationship to the midportion of the transverse duodenum. It then extends obliquely toward the right lower quadrant to insert, most often, at the cecocolic junction. Thus, anatomic continuity is established along the root of the mesentery from the pancreas to the third portion of the duodenum, jejunal loops, ileal loops, and cecum.

In this way, mesenteric planes are provided for the direct spread of extravasated pancreatic enzymes (Figs. 11-4 and 11-5):

1. Along the mesocolon to the transverse colon. Extension along its planes to its lateral limits proceeds (a) on the right, to the hepatic flexure and perhaps the distal ascending colon, and (b) on the left, to the anatomic splenic flexure just below the tip of the spleen.

2. Along the small bowel mesentery to jejunal loops and the ileocecal region.

Splenorenal Ligament

Fig. 11—2. Posterior peritoneal reflections of the left upper quadrant, demonstrating continuity of the transverse mesocolon and splenorenal ligament with the phrenicocolic ligament and the peritoneal reflections of the descending colon. The tail of the pancreas resides within the splenorenal ligament.

Peritoneal Reflections

Fig. 11—3. Left parasagittal drawing, emphasizing peritoneal reflections.

Note the tail of the pancreas within the splenorenal ligament and its continuity with the transverse mesocolon and phrenicocolic ligament.

Fig. 11—3. Left parasagittal drawing, emphasizing peritoneal reflections.

Note the tail of the pancreas within the splenorenal ligament and its continuity with the transverse mesocolon and phrenicocolic ligament.

Syndesmofity

Fig. 11-4. Opacification in vivo of continuity of mesenteric roots and bare areas in relationship to the pancreas.

In this patient who has had a right hemicolectomy and ileotransverse colostomy, fistulography strikingly illustrates communication between the root of the transverse mesocolon (TM), root of the small bowel mesentery (SBM), and the bare area of the descending colon (DC). At the site of the phrenicocolic ligament (arrow), there is communication with the transverse colon (TC) and a left cutaneous fistula.

Root The Transverse Mesocolon

Fig. 11—5. Anatomic pathways of spread from the pancreas.

Lateral drawing. The arrowed-dashed lines show the planes of spread from the pancreas (P) to the transverse colon (TC), characteristically toward its lower border, and to the small bowel (SB). TM = transverse mesocolon; SMB = small bowel mesentery.

(Redrawn from Meyers and Evans.2)

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.

Get My Free Ebook


Post a comment