The Anatomical Position of the Ileum in Health and Disease

Abstract

IT IS NOW almost six years since the attention of the medical world was attracted to the subject of regional or, more often, terminal ileitis. In that short space of time, the full clinical picture has been identified, the etiology discussed, the complications noted, and the surgical therapy amply instituted. The fact that any part or segment of the ileum might be, and often is, involved, and the recognition of participation of higher sites in the jejunum have led to the name “regional enteritis.” Yet for practical purposes the main brunt of the disease, and by far its most common form, is not a general enteritis, but a terminal ileitis, the last six to twelve inches of ileum being exclusively involved in over 90 per cent of all cases. In addition, a common complication of fistula formation frequently characterizes the disease, these fistulous tracts making their terminus in the lower right anterior abdominal wall or traversing the pelvis to appear in the perineum as perirectal or recto-vaginal fistulas. If one were to ask an anatomist, an internist, a surgeon, or even a radiologist the normal position and site of the terminal segment of the ileum, the answer would likely be hesitant, if a correct one, and would probably be based more on a general impression than upon accurate knowledge or observation. The sparsity of accurate data regarding the true anatomical position of the terminal ileum and the study of these low fistulous complications have together led us to attempt to ascertain the exact position of the terminal loop of ileum and its anatomical relationship, both in the normal body and when it is the object of a disease process. Anatomical and Embryological.—References to the exact position of the terminal ileum are sparse in anatomical textbooks and practically missing from current literature. Very few anatomists mention the subject at all; those who do—Testut, Sernoff, Piersol—place the terminal ileum deep in the pelvic fossa on the right side, though exact observations or notations are brief and insufficient from a practical standpoint. The exact anatomical location of the terminal ileum is dependent upon the normal embryological development of the ileocecum and its associated mesenteries. Ontogenetically, the ileocecum develops from that portion of the midgut which is caudad to the superior mesenteric artery, “the post-arterial segment” of Dott; according to Mall and to Huntington, the ileocecum is returned to the celomic body cavity from the physiological umbilical pouch during the tenth week of embryonal development. It assumes primarily an anterior position beneath the right lobe of the liver whence it descends to the normal adult position in the right iliac fossa. The mesentery of the ileum is formed by the fusion of the superior mesenteric artery to the posterior abdominal wall; this mesentery becomes, and is, continuous with the mesentery of the ascending colon. Both of these processes are usually effected before parturition but they may be delayed until after birth. According to Alglave, the cecum fails to descend, remaining high under the liver in almost 3 per cent of all cases. On the other hand, it may descend to the other extreme, that is, below the true pelvic brim in about 10 per cent of 1,050 specimens studied by G. M. Smith.