Table 151

Dual Embryologie Origin of the Upper and Lower Anal Canal

Upper Anal Canal (Derived from the Hindgut)

Venous drainage is by the superior rectal vein, which drains into the portal vein. Varicosities of the superior rectal vein are called internal hemorrhoids.

Tumors drain to deep lymphatic nodes (not palpable).

Sensory innervation is for stretch sensation. No pain sensation is present. Therefore, internal hemorrhoids or tumors in this area will not be accompanied by patient complaints of pain.

Motor innervation Involves autonomic control of the internal anal sphincter (smooth muscle).

Lower Anal Canal (Derived from the Proctodeum)

Venous drainage is by the inferior rectal vein, which drains into the inferior vena cava. Varicosities of the inferior rectal vein are called external hemorrhoids.

Sensory innervation is for pain, temperature, and touch. Therefore, external hemorrhoids or tumors in this area will be accompanied by patient complaints of pain.

Motor innervation involves voluntary control of the external anal sphincter (skeletal muscle).

Tumors will drain to superficial lymphatic nodes (palpable).

1. FA PC accounts for approximately 1% of all colorectal cancer cases and involves a mutation in the adenomatous polyposis coli (APC) anti-oncogene.

a. The progression from a small polyp to a large polyp is associated with a mutation in the ras proto-oncogene.

b. The progression from a large polyp to metastatic carcinoma is associated with mutations in the DCC anti-oncogene (deleted in colon carcinoma) and the p53 anti-oncogene.

2. Gardner syndrome is a variation of FAPC in which patients have adenomatous polyps and multiple osteomas.

3. Turcot syndrome is a variation of FAPC in which patients have adenomatous polyps and gliomas.

Figure 15-2. (A) Light micrograph of normal colon. The mucosa shows typical simple columnar (colonic) epithelium arranged as intestinal glands, lamina propria (Ip), and muscularis mucosa (mm). Note the straight, regular arrangement of the intestinal glands that terminate with the basement membrane intact at the muscularis mucosa. (¡3, C) Light micrograph of an adenomatous polyp. A polyp is a tumorous mass that extends into the lumen of the colon. Note the convoluted, irregular arrangement of the intestinal glands with the basement membrane intact. The epithelium is transformed into a pseudostratified epithelium with mitotic figures apparent (arrows; C is a high magnification of the boxed area in B). (B,C From East Carolina University, School of Medicine, Department of Pathology slide collection.)

Figure 15-2. (A) Light micrograph of normal colon. The mucosa shows typical simple columnar (colonic) epithelium arranged as intestinal glands, lamina propria (Ip), and muscularis mucosa (mm). Note the straight, regular arrangement of the intestinal glands that terminate with the basement membrane intact at the muscularis mucosa. (¡3, C) Light micrograph of an adenomatous polyp. A polyp is a tumorous mass that extends into the lumen of the colon. Note the convoluted, irregular arrangement of the intestinal glands with the basement membrane intact. The epithelium is transformed into a pseudostratified epithelium with mitotic figures apparent (arrows; C is a high magnification of the boxed area in B). (B,C From East Carolina University, School of Medicine, Department of Pathology slide collection.)

C. Adenocarcinomas (Figure 15-3) account for 98% of all cancers in the large intestine.

1. Mutations in the hereditary nonpolyposis colorectal cancer (HNPCC) gene, which codes for a DNA repair enzyme, have been implicated in some cases.

2. Adenocarcinomas arc characterized clinically by fatigue, weakness, change in bowel habits, weight loss, and iron-deficiency anemia. In fact, it is a clinical maxim that iron-deficiency anemia in an older man means adenocarcinoma of the colon until shown otherwise.

Figure 15-3. (A) Light micrograph of normal colon. The mucosa shows typical simple columnar (colonic) epithelium arranged as intestinal glands, lamina propria (lp), and muscularis mucosa (mm). Note the straight, regular arrangement of the intestinal glands that terminate with the basement membrane intact at the muscularis mucosa. (B, C) Light micrograph of an adenocarcinoma of the colon. Note the convoluted, irregular arrangement of the intestinal glands that have breached the basement membrane to extend deep into the submucosa and/or muscularis externa (bracket). The epithelium is transformed into a pseudostratified epithelium that grows in a disorderly pattern extending into the lumen of the gland (arrows; C is a high magnification of a typical area in B). (From East Carolina University, School of Medicine, Department of Pathology slide collection.)

Figure 15-3. (A) Light micrograph of normal colon. The mucosa shows typical simple columnar (colonic) epithelium arranged as intestinal glands, lamina propria (lp), and muscularis mucosa (mm). Note the straight, regular arrangement of the intestinal glands that terminate with the basement membrane intact at the muscularis mucosa. (B, C) Light micrograph of an adenocarcinoma of the colon. Note the convoluted, irregular arrangement of the intestinal glands that have breached the basement membrane to extend deep into the submucosa and/or muscularis externa (bracket). The epithelium is transformed into a pseudostratified epithelium that grows in a disorderly pattern extending into the lumen of the gland (arrows; C is a high magnification of a typical area in B). (From East Carolina University, School of Medicine, Department of Pathology slide collection.)

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