[New development in Crohn's disease: ++unravelling the mystery and its reinstatement as a surgically treatable condition. Part 2. Potential etiopathogenesis of "terminal ileitis" and extension of the disease to mesenteric small intestine and the colon].

INTRODUCTION

The aetiopathogenesis of terminal ileitis is still unknown, as is the cause of its spread to the small and large bowel. The aim of this study was to shed light on these unknown aspects of Crohn's disease.

CONCLUSIONS

The lack of patency of the ileal branch of the ileocolic lymphatic collector which causes terminal ileitis, usually in the earlier part of life, is likely to occur in the foetus around the 10th week of pregnancy as a result of a minor abnormality of the physiological regression of the vitelline duct. Excessive atrophy of the lymphatic network seems to occur, also affecting the rudimentary lymphatic vessels in the midgut destined to become the terminal ileum. The terminal ileitis spreads to the large bowel in an increasing percentage of cases and is directly related to duration of the disease, causing first ileitis plus right colitis, and then ileitis plus total colitis (which, however, does not include the rectum). It may also include the jejunum, causing skip lesions. This spread of lesions is not due to any genetic predisposition (that is to say, it is not predetermined in empirical terms), but rather to the extent of the lymphatic obstruction caused by the spread of immunocomplexes via the lymphatic network. This is shown by the fact that secondary lesions of the jejunum and large bowel are also typical of lymphoedema and that their spread is segmentary. In the light of these pathogenetic mechanisms, it is reasonable to assume that the spread of the process from the ileum to the colon might be prevented by prompt surgery during the initial phase of the ileitis. If these views are correct, the traditional subdivision of Crohn's disease forms into ileitis, ileocolitis and solitary colitis should be replaced by a very simple scheme showing the spread of the primary ileitis very often to ileocolitis, first confined to the right colon and then total. We cannot include either solitary colitis (not clearly defined in the literature) or anorectal Crohn's disease (whose forms have yet to be fully acknowledged) in this scheme.