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GI Path Lab 2
Reading Assignments (Robbins: Pathologic Basis of Disease, 8th Ed.)
|791 - 793||Ischemic bowel disease. Of the causes listed on page 821, low arterial flow through compromised arterial lumens is probably the most important cause for colonic ischemia. For small intestinal ischemia, mesenteric arterial emboli may be more important.|
|810 - 811||Crohn's disease. Skip the clinical parts and read them in the Medicine text.|
|793 - 796||Malabsorption syndromes (through Celiac Sprue). Skip the clinical part and get it from the discussion in lecture.|
|811 - 813||Ulcerative colitis. Skip the clinical parts and read them in the Medicine text.|
|803 - 804||Pseudomembranous colitis|
|826 - 827||Acute appendicitis. The discussion on morphology is silly. Acute appendicitis begins in the mucosa as one or more acute ulcers. From there, the inflammation extends deeper into the wall, often reaching the serosal surface, producing a coat of pus on that surface. If the disease is caught when the inflammation is still superficial, that is, confined to the mucosa and submucosa, the patient still has acute appendicitis even without neutrophils in the muscularis.|
|814 - 815||Diverticular disease|
Areas of Concentration
Upon completion of this exercise, you should be able to:
The changes are limited mainly to the mucosa. Instead of the usual straight test tube-shaped crypts, many of these crypts have bulbous projections or branches or have other peculiar shapes and sizes. This is distortion, one manifestation of chronicity. Occasional crypts have neutrophils within their epithelium, that is, cryptitis, evidence of activity. Some of the peculiar crypts contain pus within their lumens. The lamina propria is highly cellular with many plasma cells and eosinophils extending from beneath the surface to the muscularis mucosae and even into the superficial submucosa. These cells also are also evidence of chronicity. There is no deeper inflammation, except for a few lymphoid nodules arranged in a row in the junction between the mucosa, muscularis mucosae, and superficial submucosa. This is an example of the type of ulcerative colitis that does not cause significant ulcers but, instead, the disease nibbles away at the mucosa, producing more and more distortion and eventual loss of crypts, that is, atrophy.
Crohn's Disease of the Small Intestine
The small intestinal villi are strikingly distorted. Many are huge, edematous structures, while others are elongated and filled with a mixture of inflammatory cells including many plasma cells. The crypts are also irregularly shaped, and at the base of the mucosa, some of them have epithelium, which contains granular pink-staining mucus, identical to that seen in glands in the gastric antrum or in Brunner's glands of the duodenum. This is a metaplasia that only seems to occur at the edges and bases of ulcers in the intestines, especially the small intestine. Some of the mucosa is ulcerated and converted to granulation tissue covered by pus. The muscularis mucosae are irregularly thickened, with muscle fibers and bundles extending into the submucosa in various directions and producing occasional lumps. The submucosal nerves are huge, that is, hypertrophied. Finally, there are aggregates of lymphoid cells or lymphoid nodules scattered throughout the submucosa. A few of these penetrate the muscularis propria, and rare ones can be found in the subserosa. Occasional slides may have loose granulomas with macrophages and even giant cells in the submucosa. This small intestinal Crohn's disease is not transmural in these slides, although it was transmural in other parts of the small bowel.
Acute Ischemic Colonic Diseases
Most of the abnormalities are confined to the mucosa. There are several patches of mucosa in which the lamina propria appears granular and debris-filled, and the crypts have disappeared. Nevertheless, the outline of the mucosa persists and is of the same thickness as the intact mucosa. In other similar areas, neutrophils fill this mucosal outline. In still other areas, there are a few residual basal crypts that are small and are lined by epithelium with enlarged nuclei and very little cytoplasmic differentiation. These are regenerative, and they are trying to reconstitute the mucosa. Other evidence of regeneration is the syncytial surface epithelium that seems to be trying to cover denuded mucosa.
In a few places, especially at the base of the totally necrotic mucosa, neutrophils extend into the submucosa and occasionally even into the muscularis propria where they are associated with loss or lysis of muscle fibers. In all sections, the submucosa is thick and edematous.
There are several patches in which the mucosa is both partly or completely necrotic and replaced by neutrophils. In the partially necrotic areas, some of the superficial crypts are dilated and filled with a mixture of pus and mucin that pours onto the surface as an exudate that covers the surface. In the areas of complete mucosal necrosis, neutrophils extend into the submucosa.
Appendix: Acute Appendicitis
The answers to the path lab questions will be posted approximately 48-72 hours after the lab sessions. These are abbreviated answers, not a full discussion of the topics. You can find them in the M2 CTools site resources. In the folder for each sequence the will be a folder called 'Path Lab Resources'