5 Science and Practice of Medicine.
Gangrene and ulceration, however, do not always follow intussusception. The mesenteric injuries may be sufficient to produce congestion and exudation, and the patient survive the invagination for weeks, and death eventually occur without sloughing or ulceration; or spontaneous reduction of the invagination may take place and recovery of the patient follow. The last termination must be rare, and impossible when firm adhesion between the serous surfaces has taken place; but that it does exceptionally occur is proved by cases where the diagnosis of intussusception was undoubted, the invagination being felt in the rectum or seen prolapsed through the anus. The most common termination, if the patient survives, is mortification of the invaginated part and separation in mass or by shreds or fragments.
Intussusception may occur in any portion of the intestinal canal, but some points are more liable to it than others. 56 per cent. of the cases collected by Brinton were ileo-cæcal; in 32 per cent. the small intestine alone was involved; 28 iliac and 4 jejunal; in 12 per cent. the colon, including its sigmoid flexure, was the part implicated.
When the rectum is involved, it usually forms the outer layer of the invagination, the middle and inner layers being formed by the bowel which has passed from above into it; when prolapse of the rectum itself occurs, the mucous membrane is generally alone involved, but along with this the muscular coat may also descend and a true invagination of the rectum be found.
The most common variety of intussusception is the ileo-cæcal. It is in this form that we find the greatest length of bowel involved. This invagination begins generally at the ileo-cæcal valve, the lips of which at first turn toward, and descend into, the cavity of the cæcum, drawing with them the end of the ileum; in this case the valve forms the lowest point of the invagination. If the invagination continues, the end of the cæcum is next inverted; and if the process still goes on, more and more of the colon is invaginated, until in some rare cases it traverses the whole of the large intestine, appearing just above or even protruding through the anus. In this variety the vermiform appendix lies between the middle and inner layers of the intussusception, and its opening, usually stretched and enlarged by the inverted cæcum and inflammatory effusion, is found close to the ileo-cæcal orifice. In this intussusception the cæcum and colon are large and roomy, and the invaginated portion not so liable, as it is when the small intestine is alone implicated, to strangulation and sloughing; nor is there seen in ileo-cæcal intussusception, unless the portion of bowel involved is very short, the marked curvature of the invaginated portion so commonly found in the small intestine. In the ileo-cæcal form it is twisted or much convoluted rather than bent.
Another variety of ileo-cæcal invagination—very rare, however—is where the ileo-cæcal orifice does not descend into the cavity of the cæcum, but the lower end of the ileum passes through the valve into the large intestine. In this instance the invaginated portion is tightly compressed by the valve, and strangulation is speedy and complete. An invagination may occur in the lower part of the ileum, and the inner and middle layers pass on to the ileo-cæcal valve, and be arrested at that point, and afterward, in consequence of violent peristaltic action, the whole intussusception, inner, middle, and outer layers, be invaginated into the colon. In this way the invagination becomes doubled.
While intussusception may occur in either sex and at all periods of life, it happens nearly twice as often in males as in females, and is most frequently seen in childhood. Leichtenstern6 found in his statistics of 473 cases that one-half were seen in children under ten years old, and one-fourth of all intussusceptions occurred in children from four to twelve months old. Invagination of the small intestine is found almost exclusively in adults. Brinton from his records gives the mean age of its occurrence 34.6 years. According to the same author, the average age of ileo-cæcal invaginations is 18.57 years, and one-half of all cases of this form of intussusception observed by him were in children under seven years of age. Leichtenstern states that the lower part of the ileum is the most frequent site of invagination in the small intestine, and the descending colon and sigmoid flexure the most common portion involved in intussusception occurring in the large intestine.
6 Op. cit.
The mechanism of intussusception is probably not always the same. The following is thought to be the most frequent process: A segment of bowel becomes paralyzed by local peritonitis, some injury, diarrhoea, or colic, and while in this state a segment of bowel above is subjected to violent peristaltic action, and is forced into the unresisting portion below. In this case the paretic segment forms the outer or receiving layer of the intussusception. Leichtenstern believes that the paretic portion is turned in and invaginated into the normal bowel below, and that the clinical course of intussusception and post-mortem appearance correspond with this explanation. If such is the case, the paralyzed portion forms the inner layer, and the active bowel below the receiving layer. Another theory, which applies with much force to the most common of all invaginations—viz. the ileo-cæcal—is, that as violent anal tenesmus produces prolapse of the rectum, so prolonged and powerful tenesmus at the ileo-cæcal opening may cause prolapse of the lips of this orifice, and, eventually, invagination of the ileum, or of both this and the cæcum, into the colon. When we remember that the ileo-cæcal valve is furnished with a sphincter muscle, the analogy is complete. The idea so long entertained that intestinal worms may occasion invagination of the bowel has generally been abandoned. A polypoid tumor, by dragging down the portion of bowel to which it is attached, may produce invagination; and Brinton's statistics give 5 per cent. of cases of intussusception from this source. An examination of a larger number of cases would probably show a much smaller percentage due to this cause.
A majority of cases of intussusception, however, take place suddenly, without previous diarrhoea, colic, traumatism, or ill-health of any kind, and probably occur without any tenesmus or paresis of a portion of bowel. It may be that the longitudinal fibres of a segment of gut contract, dilating and shortening a portion of the bowel; while this part is distended a portion immediately above may be lengthened and narrowed by contraction of the circular fibres, and violent peristalsis going on at this moment, aided, possibly, by contraction of the muscular wall of the abdomen, forces the upper and narrow segment into the lower and dilated one.