Paper - Imperfect torsion of the intestinal loop
|Embryology - 6 Dec 2019 Expand to Translate|
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Imperfect Torsion of the Intestinal Loop
By Douglas G. Reid, M.B., Ch.B. Edin., B.A. Trin. Coll. Camb.,
Demonstrator of Anatomy in the University of Cambridge, Trinity College.
The loop referred to in the title is the embryonic intestinal loop, which in the case under notice (see ﬁgure) was minus the transverse colon and plus the third portion (pars inferior) of the duodenum. The neck of the loop was formed by the second part (pars descendens) of the duodenum and the right end of the transverse colon. But the disposition of the gut was unusual in that the limb formed by the large intestine, and that formed by the small, lay the former on the left, the latter on the right of the superior mesenteric artery. Such, as regards the bowel, was the outstanding feature of this interesting condition. There was no indication of old peritonitis or other pathological condition to take away the value of the picture. The body was that of a man over sixty years of age who died of cerebral haemorrhage, and presented no other outstanding anomalies than those of the intestinal canal whose details are here recorded. The stomach was more attenuated in shape than usual. There was a very well-developed hepatocolic ligament (see fig., A), and the foramen of Winslow was normal. The great omentum (see fig., B) presented its usual inseparable attachment to the middle portion of the colon and mesocolon, and was similarly fused with the upper portion of the ascending colon.
The rest of the duodenum requires a more detailed description. It was unusually mobile and lay altogether to the right of the mesial plane, was not related in front to the colon, to the root of the mesentery, or to the jejunum. The descending portion had the usual direction, and lay about 5 cms. from the right end of what, from its position, may be considered to represent the transverse colon, and with it formed the neck of the loop of bowel. The short third part of the duodenum lay entirely posterior to the second portion of the duodenum, from which it was separated by the head of the pancreas. Its direction was to the left and slightly upwards. Reaching the bifurcation of a very short common stem of the inferior pancreatico-duodenal artery and of the uppermost of the vasa intestini tenuis, the bowel at this level, close to the right side of the superior mesenteric artery, turned acutely to the right and downwards, becoming jejunum. This for quite 4 cms. was also covered in front by the second portion of the duodenum (see ﬁgure). But wedged in between them, and separating them to a large extent from one another, was the lower part of the head of the pancreas.
The surfaces of the duodenum, jejunum, and pancreas, which were in apposition with each other, were bare as regards peritoneum. The posterior aspect of the third portion of the duodenum was free behind, the peritoneum leaving the upper border of this aspect to reach the posterior abdominal wall along an almost horizontal line which formed the upper duodenal portion of the line of soldering (see fig., D) to be described. Inasmuch as the second part of the duodenum, head of the pancreas, and jejunum came into antero-posterior relation with one another the mesentery of the last named was common to all. All were thus equally mobile. Above the jejunum a lamina of peritoneum (part of the originally right lamina of the mesoduodenum), lying in the frontal plane, and about 2 cms. long, connected the second part of the duodenum to the posterior abdominal wall quite to the right of the superior mesenteric artery. Upon the front of this lamina was a rather well-developed muscle of Treitz embedded in connective tissue, representing part of the originally left lamina of the mesoduodenum.
To become continuous with the muscular wall of the third portion of the duodenum this muscle passed downwards upon the right side of the superior mesenteric artery. The connective tissue and muscle just described were covered in front by the posterior (ordinarily anterior) surface of the head of the pancreas, just at its upper part. But, covering this surface of the head of the pancreas, and intervening, was a fascia which also represented the connective element of the original left lamina of the mesoduodenum. The third portion of the duodenum was sessile. Of the appendages of the duodenum the liver, at least, presented nothing unusual. Practically the whole of the head (see ﬁg., PA) of the pancreas lay clasped between duo- denum in front and duodenum and jejunum behind. It did not lie behind either of the superior mesenteric vessels; indeed, its left border, projecting somewhat beyond the descending portion of the duodenum, overlapped the artery in front. This border, however, owing to the peculiar disposition of the duodenum, corresponded to the right border of the usual adult head of the pancreas. In other words, there was absence of the little pancreas of Winslow (processus uncinatus pancreatus). Perhaps a mere rudimentary development in connection with the right (which corresponded to the usual left) border of the head of the pancreas represented it. Nevertheless, the condition of matters present only went to conﬁrm the statements made to the effect that the development of the pancreatic uncus corresponds to the degree of leftward shift of the jejunal end of the duodenum.
It may be stated at once that the intestinal loop—excluding the already described third portion of the duodenum - possessed a dorsal lamina, which had acquired a narrow line of soldering, and a ventral (the loop, of course, was in the frontal plane) lamina of peritoneum. The small intestinal limb of the loop was without a Meckel’s diverticulum. Tracing the dorsal lamina of the peritoneum (mesentery) in connection with the small intestine, it was found to pass to a line (see fig., D) of most deﬁnite soldering on the posterior abdominal wall and inner surface of the right wall of the pelvis. Starting above in continuity with the duodenal line of soldering it passed, with a gentle curve, downwards and to the left, then downwards and to the right.
After lying for some distance upon the front of the aorta and in the middle line, it went medial to the right common iliac artery into the pelvis. The ventral lamina (see fig., V), lying upon the subjacent superior mesenteric artery and its branches, was carried directly — by which is meant that it had no line of soldering whatsoever—to the ascending colon. Thus nothing really resembling the root of “ the mesentery ” of the usual adult existed. The caecum (see fig., F) lay inverted and wholly intrapelvic; it presented its usual adult form. The lower part of the ascending colon was also intrapelvic. In obtaining this position it had tended to shove the caecum up again into the abdomen, and had so inverted it. The ascending colon (see ﬁg., E), save for its lower end, lay entirely to the left of the mesial plane. It coursed upwards and to the left, then upwards and to the right, going over into the transverse colon at the neck of the loop.
Peritoneal Relations. Examining the intrapelvic part of the ascending colon, it was found that the ﬁngers could be introduced behind it into a number of peritoneal fossae, and in these could be pushed, without rupture of peritoneum, right up to the intrapelvic line of soldering, where their progress was arrested. Therefore the dorsal lamina of the peritoneum of this portion of the intestinal loop, save for a narrow line of soldering to the pelvic wall, and some imperfect blending with the parietal pelvic peritoneum resulting in the formation of a row of ﬁve well-marked fossae, existed in its primitive, free, unfused condition. The abdominal portion of the ascending colon had acquired a ﬂimsy, bloodless connexion with the parietal peri- toneum, and its upper part was related, as already described, to the great omentum, and thus were concealed the true relations of the parts. An opening having been made through the two layers of the great omentum (at + in ﬁgure), the ﬁngers could be passed behind the ascending colon into a peritoneal cavity bounded in front by the two lamina of peritoneum connected with the ascending colon, between which blood—vessels were lying, furnishing thus a clue to the situation; bounded behind by the parietal peritoneum; and to the right by the line of soldering (see D in fig.). Below, it reached downwards as far as the bifurcation of the aorta; and ﬁngers introduced into the two uppermost peritoneal fossae could be passed upwards over the pelvic brim to this level, so as to meet, only separated by the walls of the fossae, the ﬁngers in the compartment. In all situations the ﬁngers could be pushed, without tearing of peritoneum, right up to the line of soldering, where their advanc'e was barred. Thus the intra-abdominal dorsal lamina of the peritoneum of the loop also existed in its primitive, free condition, except for the narrow line of soldering. Above, at the level of the origin of the artery of the transverse colon (see fig., (1)), the dorsal lamina passed into the lower lamina of the mesentery of the colon with the upper lamina, of which the ventral lamina of the peritoneum of the loop, of course, became continuous.
The part corresponding to the normal transverse colon (see ﬁg., K) was not in the common sessile condition. Its extremities lay in practically the same horizontal plane. One, as already mentioned, formed part of the neck of the intestinal loop. The splenic ﬂexure was in its usual adult position, inferior to the phreno-colic ligament (see fig., 0). Transverse only for a short extent of length, this part of the colon for the rest of its course took the form of a loop whose limbs were closely apposed and, indeed, bound together by peritoneum, and ﬁxed by a common mesentery to the posterior abdominal wall. The lower extremity of this interesting colic loop descended an inch or so below the inter-tubercular plane. The root of its mesentery skirted, from below upwards—its lower end (see fig. M), in truth, passing on to the side of the pelvic colon—the right aspect of the iliac, and the similar aspect of the descending colon.
All the bowel caudalwards from the splenic ﬂexure presented no noteworthy feature. The descending colon lay dorsal to the ascending limb of the colic loop; neither it nor the iliac colon possessed a mesentery The intersigmoid fossa (see ﬁg., S) was well developed.
Vascular Relations. The superior mesenteric artery (see ﬁg., SM) as it entered the neck of the intestinal loop lay to the left of the duodenum and head of the pancreas. The duodenum was, therefore, not within the limbs of the usual superior mesenteric and aortic A. Nor was the artery within a pancreatic embrace. The vessel, almost immediately crossing the line of soldering so as to lie thereafter entirely to its right, took a course curved with convexity directed to the right. The superior mesenteric vein lay from below upwards ﬁrst to the right, then behind, and to the left of the artery, overlapping it somewhat in front, and was joined, considerably below the neck of the pancreas, by the splenic vein. The portal vein (P) so formed crossed in front of the artery. If we imagine the intestinal torsion to be completed, the usual relation of the vein to the artery would be obtained. The arteries of the jejunum and ileum (and a large accessory hepatic artery) had their origin from the right convex aspect of the superior mesenteric. The very short common stem of the inferior pancreatico-duodenal artery, and of the uppermost artery to the jejunum, arose from its right and posterior aspect. The ileo-colic (see fig., (3)), and a common stem of the arteries of the transverse and ascending colons, took origin from its left concave aspect. The latter coursed to the left and upwards, and at the line of soldering divided into its two parts. The artery of the ascending colon (see fig., (2)) followed closely the line of soldering, but diverged to its left below; it was placed throughout between peritoneal laminae. An especially noted point, then, was that the peritoneum of the intestinal loop was free from adhesion to the right and left of the artery of the ascending colon in part of its course. The branches of the artery of the ascending colon arising from its left aspect coursed to the left—not_ behind the parietal peritoneum, but between the laminae of peritoneum already described. The artery of the transverse colon (middle colic (see fig., (1)) entered at once between the two laminae of the mesentery of the transverse portion of the transverse colon. It gave here a branch to this part, and a second which, leaving the mesentery, coursed behind the perietal peritoneum to enter the mesentery of the colic loop. The artery of the descending colon (left colic) also entered this mesentery to supply the colic loop before supplying, by means of one of its two terminal branches, the adjacent descending colon.
Cite this page: Hill, M.A. (2019, December 6) Embryology Paper - Imperfect torsion of the intestinal loop. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Imperfect_torsion_of_the_intestinal_loop
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