Lower Small Bowel Mesentery Terminal Ileum and Cecum Radiologic Features

The root of the small bowel mesentery extends from the left side of the second lumbar vertebra downward to the right, across the aorta and inferior vena cava, to the right sacroiliac joint, a distance of only about 15 cm. From

Penn Small Intestine Cancer

Fig. 4—109. Metastatic seeding in the pouch of Douglas.

Double-contrast study demonstrates infiltrations and mucosal tethering involving the rectosigmoid junction anteriorly from metastatic ovarian carcinoma. (Courtesy of Stephen Rubesin, M.D., Hospital of the University of Pennsylvania, Philadelphia.)

Fig. 4—109. Metastatic seeding in the pouch of Douglas.

Double-contrast study demonstrates infiltrations and mucosal tethering involving the rectosigmoid junction anteriorly from metastatic ovarian carcinoma. (Courtesy of Stephen Rubesin, M.D., Hospital of the University of Pennsylvania, Philadelphia.)

the root, a series of mesenteric ruffles support the small bowel loops (Figs. 4-113 and 4-114). These fanlike mesenteric extensions contribute to the characteristic undulating nature and position of the coils of small bowel, which averages 15-20 ft in length. Distally, the mesentery inserts most often at the cecocolic junction. A series of peritoneal recesses is thus formed extending along the right side of the ruffled small bowel mesentery obliquely toward the right lower quadrant of the abdomen. I have shown that these also serve to pool collections of ascitic fluid1,3,4 (Figs. 4-115 and 4-116). Spread here occurs in a series ofcascades or rivulets from one mesenteric ruffle to the next, directed along the axis of the small bowel mesentery toward the right lower quadrant in relation to distal ileal loops and the cecum (Fig. 4-117). It is here, within the lower recesses of the small bowel mesentery, that the most consistent pool of fluid forms before overflow into the pelvis occurs.

Seeded deposits lodging within the lower recesses of the small bowel mesentery in the right infracolic space are clinically identifiable in over 40% of cases by their displacement of distal ileal loops, perhaps with pressure effects also upon the medial contour of the cecum and ascending colon.

Symmetric growth within multiple adjacent mesen-teric recesses results in discrete separation of ileal loops in the right lower quadrant. Angulated tethering of mucosal folds indicates associated fibrous response. Significantly, these and any serosal masses are therefore identifiable on the concave borders, which are suspended by the mesenteric ruffles.4 The narrowed loops may be aligned in a parallel configuration that I describe as "palisading" (Fig. 4-118). The axis of the serosal masses as well as of the affected intestinal loops conforms to the axis of the small bowel mesentery. As the seeded growths become somewhat larger, they may displace the bowel loops in a gently arcuate manner (Fig. 4-119). The striking symmetry of size, mass displacement from the mesenteric border of the loops, and orientation to the mes-enteric ruffles in the right lower quadrant characterize the process. The seeded metastases on the serosal aspect of ileal loops in the right lower quadrant are typically localized to the concave mesenteric borders.

If the desmoplastic response to the seeded metastases is severe, marked fixation and angulation of ileal loops in the right lower quadrant result (Figs. 4-120 and 4121). The most extreme fibrous reaction has been encountered in metastatic seeding from pancreatic carcinoma and mucin-producing gastric carcinoma. Serosal mass displacement may remain evident. The points of acute angulation tend to conform to the axis of the mesentery. Despite the narrowing and sharp course, obstruction may not be conspicuous.

Caecum Volgus

Fig. 4-110. Progressive changes of metastatic seeding in the pouch of Douglas.

Deposits from a primary carcinoma of the splenic flexure of the colon result in increasing mass impression on the rectosigmoid.

(b and c) 5 months and 1 year, respectively, after (a).

Fig. 4-110. Progressive changes of metastatic seeding in the pouch of Douglas.

Deposits from a primary carcinoma of the splenic flexure of the colon result in increasing mass impression on the rectosigmoid.

(b and c) 5 months and 1 year, respectively, after (a).

Metastatic Seeding Pouch Douglas

Fig. 4—111. Metastatic seeding in the pouch of Douglas.

Sagittal MR image shows seeded deposits from a primary carcinoma of the ovary in the rectouterine pouch of Douglas (PD). R = rectum; S = sigmoid colon; U = uterus; B = urinary bladder.

(Courtesy of Michiel Feldberg, M.D., Ph.D., University of Ultrecht, The Netherlands.)

Tumor The Pouch Douglas

Fig. 4—111. Metastatic seeding in the pouch of Douglas.

Sagittal MR image shows seeded deposits from a primary carcinoma of the ovary in the rectouterine pouch of Douglas (PD). R = rectum; S = sigmoid colon; U = uterus; B = urinary bladder.

(Courtesy of Michiel Feldberg, M.D., Ph.D., University of Ultrecht, The Netherlands.)

Fig. 4—112. Metastatic seeding in the pouch of Douglas.

Sagittal MR image in a patient with ovarian carcinomatosis shows implanted tumor filling the rectouterine pouch (arrows) and tumor plaques adhered to the anterior uterine wall (arrowheads). The urinary bladder (UB) is collapsed and compressed by a large amount of ascites. (Reproduced from Auh et al.10)

Human Mesentery

Fig. 4-113. The small bowel mesentery, illustrating its ruffled nature.

A series of peritoneal recesses is formed along its right side. (Reprinted with permission from Kelly HA: Appendicitis and Other Diseases of the Vermiform Appendix. Lippincott, Philadelphia, 1909.)

Fig. 4-113. The small bowel mesentery, illustrating its ruffled nature.

A series of peritoneal recesses is formed along its right side. (Reprinted with permission from Kelly HA: Appendicitis and Other Diseases of the Vermiform Appendix. Lippincott, Philadelphia, 1909.)

Fig. 4-114. The small bowel mesentery.

CT section through the lower abdomen containing ascites clearly shows the fat-laden small bowel mesentery with its vessels (arrows).

In the right lower quadrant, mesenteric ruffles support loops of ileum (I).

Fig. 4-114. The small bowel mesentery.

CT section through the lower abdomen containing ascites clearly shows the fat-laden small bowel mesentery with its vessels (arrows).

In the right lower quadrant, mesenteric ruffles support loops of ileum (I).

Which Quadrant The Illeum

If no significant fibrous reaction is elicited as the metastases increase in size, gross extrinsic mass displacement may be shown (Figs. 4-122 through 4-124). The mes-enteric masses, however, tend to be multiple, and they maintain their relationship to the lower small bowel mesentery (Fig. 4-125). They displace ileal loops predominantly inferiorly and medially and may exert pressure on the ascending colon medially and the proximal transverse colon inferiorly.

Since the small bowel mesentery most commonly inserts at the cecocolic junction, the effects of seeded metastases on the cecum are shown typically on its medial and inferior contours.4 The level of involvement is thus usually below the ileocecal valve in the caput of the cecum. The extrinsic mass indenting the cecum may be smooth or lobulated (Figs. 4-126 and 4-127), ofvariable size (Fig. 4-128), and at times, may encircle the cecum (Fig. 4-129). The mass changes on the cecum are not, in themselves, specific for seeded metastases and may simulate appendiceal abnormalities, other mesenteric masses, or even primary lesions of the cecum. However, they are almost invariably accompanied by the more characteristic changes involving distal small bowel loops. If first appreciated on a barium enema study, these can be identified by reflux into the terminal ileum (Figs. 4-

127 and 4-128) or in a subsequent small bowel series. The association of findings may occasionally closely simulate granulomatous enterocolitis.44 (Fig. 4-130). The small bowel alterations are usually not difficult to distinguish from other common disease states. The lack of inflammatory features, such as spasm, ulcerations, and sinus tracts, and the characteristic spectrum of changes help in the differential diagnosis from regional enteritis, tuberculosis, amebiasis, and peritoneal adhesions. When the seeded metastases are diffuse throughout the small bowel (Fig. 4-131), the changes secondary to the des-moplastic process may resemble carcinoid or radiation enteritis. Fixed angulation and alternating areas of narrowing and dilatation are accompanied by serosal masses identifiable on the mesenteric borders and conspicuous tethering of mucosal folds.

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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  • Safa
    Where is small bowel loop under cecum?
    7 years ago

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