ISCHEMIC BOWEL DISEASE

Ischemic lesions may be restricted to the small or large intestine, or may affect both, depending on the particular vessel(s) affected. Acute occlusion of one of the three major supply trunks

of the intestines—celiac, superior mesenteric, and inferior mesenteric arteries—may lead to infarction of several meters of intestine. However, insidious loss of one

Figure 17-48Acute ischemic bowel disease. Schematic of the three levels of severity, diagrammed for the small intestine.

Figure 17-49Infarcted small bowel, secondary to acute thrombotic occlusion of the superior mesenteric artery.

Figure 17-50Mucosal infarction of the small bowel. The mucosa is hemorrhagic, and there is no epithelial layer. The remaining layers of the bowel are intact.

Figure 17-51Chronic ischemia of the colon, resulting in chronic mucosal damage and a stricture.

Figure 17-52Diverticulosis. A, Section through the sigmoid colon, showing multiple sac-like diverticula protruding through the muscle wall into the mesentery. The muscularis propria in

between the diverticular protrusions is markedly thickened. B, Low-power photomicrograph of diverticulum of the colon, showing protrusion of mucosa and submucosa through the muscle

wall. A dilated blood vessel at the base of the diverticulum was a source of bleeding; some blood clot is present within the diverticular lumen.

TABLE 17-11-- Major Causes of Intestinal Obstruction

Mechanical Obstruction

Adhesions

Hernias, internal or external

Volvulus

Intussusception

Tumors

Inflammatory strictures

Obstructive gallstones, fecaliths, foreign bodies

Congenital strictures; atresias

Congenital bands

Meconium in mucoviscoidosis

Imperforate anus

Pseudo-obstruction

Paralytic ileus (e.g., postoperative)

Vascular—bowel infarction

Myopathies and neuropathies (e.g., Hirschsprung)

Figure 17-53Schematic depicting the four major causes of intestinal obstruction: (1) Herniation of a segment in the umbilical or inguinal regions; (2) adhesion between loops of intestine;

(3) intussusception; (4) volvulus formation.

TABLE 17-12-- Tumors of the Small Intestine and Colon

Non-neoplastic (Benign) Polyps

Hyperplastic polyps

Hamartomatous polyps

• Juvenile polyps

• Peutz-Jeghers polyps

Inflammatory polyps

Lymphoid polyps

Neoplastic Epithelial Lesions

Benign

• Adenoma *

Malignant

• Adenocarcinoma *

• Carcinoid tumor

• Anal zone carcinoma

Mesenchymal Lesions

Gastrointestinal stromal tumor (GIST) (gradation from benign to malignant)

Other benign lesions

• Lipoma

• Neuroma

• Angioma

Kaposi sarcoma

Lymphoma

* Benign and malignant counterparts of the most common neoplasms in the intestines; virtually all lesions are in the colon.

angiomas, and rare hamartomatous mucosal lesions comprise the remainder. One of the enigmas of medicine is the rarity of malignant tumors of the small intestine—annual U.S. death rate

is under 1000, representing only about 1% of gastrointestinal malignancies. Small intestinal adenocarcinomas and carcinoids have roughly equal incidence, followed in order by

lymphomas and sarcomas. As the latter three exhibit a broader distribution than the small intestine, they are discussed later.

Adenomas

Adenomas account for approximately 25% of benign small intestinal tumors, with benign mesenchymal tumors (especially leiomyomas), lipomas, and neuromatous lesions following in

frequency. Most adenomas occur in the region of the ampulla of Vater. The usual presentation is that of a 30- to 60-year-old patient with occult blood loss, rarely with obstruction or

intussusception; some are discovered incidentally during radiographic investigation. Patients with familial polyposis coli (discussed later) are particularly prone to developing

periampullary adenomas. Macroscopically, the ampulla of Vater is enlarged and exhibits a velvety surface ( Fig. 17-54 ). Microscopically, these adenomas resemble their counterparts in

the colon (discussed later). Frequently, there is extension of adenomatous tissue into the ampullary orifice, rendering surgical excision difficult, short of a pancreatoduodenectomy to

remove the entire ampullary region. Like its counterpart in the colon, the small intestinal adenoma is a premalignant lesion. The adenoma-carcinoma sequence has been demonstrated in

small intestinal tumors.

Figure 17-54Adenoma of the ampulla of Vater, showing exophytic tumor at the ampullary orifice.

Figure 17-55Diagrammatic representation of two forms of sessile polyp (hyperplastic polyp and adenoma) and of two types of adenoma (pedunculated and sessile). There is only a loose

association between the tubular architecture for pedunculated adenomas and the villous architecture for sessile adenomas.

TABLE 17-13-- Hereditary Syndromes Involving the Gastrointestinal Tract

Date: 2016-04-22; view: 722