The esophagus is a muscular tube approximately 25-cm long connecting the pharynx to the stomach, beginning at the level of C5/6 and terminating at its entrance to the stomach at the gastroesophageal junction (Fig. 67.1). The esophageal wall is composed of four layers: (a) an external fibrous layer, (b) a muscular layer, (b) a submucosal layer, and (d) an inner mucous membrane. The esophagus has an inner circular and outer longitudinal muscle coat that is predominantly striated within the upper third, gradually converting to smooth muscle fibers toward the gastroesophageal junction. The mucosal lining of the esophagus is stratified squamous epithelium throughout its length, only changing to columnar epithelium at the gastroesophageal junction.

The stomach is a muscular bag that is roughly J-shaped with a cranial “cardiac” and caudal “pyloric” orifice. Two curvatures, the lesser and greater curves, connect these orifices. The stomach itself is divided into the following three parts (Fig. 67.3):

The muscular wall of the stomach contains three muscle layers. The longitudinal fibers are the closest to the stomach’s external surface and are concentrated around the curvatures of the stomach. The incomplete middle circular fibers are thickened at the pylorus to form the pyloric sphincter. The oblique fibers form the innermost coat. The innermost surface of the stomach comprises the single layer columnar epithelium, which dips down into the connective tissue lamina propria to form multiple small glands, secreting mucus, pepsin, hydrochloric acid, and intrinsic factor.

The small bowel can vary between 4 and 6 m in length. The jejunum begins at the duodenojejunal flexure and represents approximately two-fifths of the proximal small bowel with a gradual transition to ileum. The ileum terminates at its junction with the cecum at the ileocecal junction (Fig. 67.5). These bowel loops are freely mobile and are connected to the posterior abdominal wall by a fan-shaped peritoneal fold called the small bowel mesentery. The jejunum has numerous prominent folds that encircle the lumen called the plicae circulares. These are fewer in number and less prominent in the ileum.

Just deep to the mucosa is the muscularis mucosae, comprising the inner circular and outer longitudinal muscle fibers. Separated by the submucosa is the muscularis propria, again composed of inner circular and outer longitudinal muscle fibers. The bowel loops are then invested with a serosal layer. Columnar epithelium lines the whole small bowel, dipping downward to form glandular structures known as the crypts of Lieberkühn, but also thrown upward between the gland openings to form innumerable finger-like projections (villi). Villous cells are responsible for secreting mucus and absorbing nutrients.

The colon consists of four parts: (a) the ascending colon, (b) the transverse colon, (c) the descending colon, and (d) the sigmoid colon (Fig. 67.7). The ascending and descending colon are retroperitoneal in location, while the transverse and sigmoid colon are connected to the posterior abdominal wall by a mesentery known as the transverse and sigmoid mesocolon. The colon has a sacculated appearance owing to the presence of incomplete folds (haustra). The outer longitudinal smooth muscle runs as three separate strips (taenia coli). The primary function of the colon is to store waste and reabsorb water.

The rectum commences anterior to the S3 vertebral body and ends at its communication with the anal canal.

The upper third is covered by peritoneum anteriorly and laterally, the middle third by peritoneum anteriorly only, with the lower third having no peritoneal covering. The taenia coli of the colon fuse at the rectosigmoid junction, with the rectum itself containing four longitudinal mucosal folds (columns of Morgagni). The rectum is surrounded by the perirectal fat containing blood vessels and lymph nodes, which itself is encased by the perirectal (mesorectal) fascia. The mesorectal fascia represents the circumferential resection margin, which is important for surgical planning; tumor within less than 1 mm of the circumferential resection margin is associated with a poorer prognosis. This mesorectal fat is less prominent anteriorly and caudally to the rectum.

At least 90% of esophageal tumors are either squamous cell carcinomas or adenocarcinomas. Esophageal cancer is the eighth most common cancer worldwide and sixth most common cause of cancer mortality.¹ The highest incidence rates (between 50 and 100 cases per 100,000 population per year) are in northern China, northeastern Iran, and South Africa. It is rare under the age of 30 years, with mean age at diagnosis of 68 years in the United States.² In the Western world, the incidence of adenocarcinoma is increasing and is the most common histopathologic type, although in developing countries, nearly all cancers are squamous in origin. Squamous cell tumors are evenly distributed between the middle and distal thirds of the esophagus, usually in association with alcohol and tobacco consumption. They can appear as infiltrating, polypoid, ulcerative, or superficial spreading lesions. There is a marked tendency to invade adjacent mediastinal structures, because there is no protective serosal layer. Less than 30% of tumors are adenocarcinomas, with approximately 80% of these found toward the lower third of the esophagus. These are thought to usually arise de novo from short segment distal Barrett esophagus. For advanced esophageal tumors, the use of surgery alone or resection followed by radiotherapy (with or without chemotherapy) has failed to improve prognosis, which remains poor. For these patients, chemoradiotherapy followed by surgery or chemoradiotherapy alone has been employed in an effort to reduce both local recurrence and distant spread and to improve survival. The most common multimodality therapy consists of a combination of 5-fluorouracil and cisplatin.

Malignant gastric tumors are adenocarcinomas in 95% of cases (the remaining being mostly lymphoma, gastrointestinal stromal tumors, and carcinoid). Gastric cancer is the fourth most common cancer worldwide and the second leading cause of cancer-related death.^3,4 The highest incidence rates are in Japan and Korea. Because of mass screening programs in Japan, the mortality rates for gastric cancer in men have decreased by more than 50% since 1970, with a 5-year survival rate of 95% for early tumors. In contrast, the 5-year survival rates in the United States and Europe are less than 20%, owing to later presentation. There are two types of tumor: a differentiated intestinal type, usually affecting the distal stomach and demonstrating tubular or papillary glands (60%), and an undifferentiated diffuse type, distributed throughout the stomach with a worse prognosis (40%). The intestinal type is associated with older males, while the diffuse type has no gender predilection and occurs in a younger population. Overall, the location of gastric tumors is approximately evenly distributed between the antrum, body, and fundus or cardia. The incidence of the cardiac type has risen by five- to sixfold in the past 30 years in developed countries. Most gastric carcinomas are polypoid or ulcerated lesions, or less commonly scirrhous lesions, that diffusely infiltrate along the gastric wall. A demonstrable link between Helicobacter pylori colonization and distal tumors has been shown, with other risk factors including diet, smoking, atrophic gastritis, and pernicious anemia.

For early gastric cancer (stages 0, I, and II), subtotal or total gastrectomy is performed (depending on the site and extent of involvement) along with regional lymphadenectomy. For stage III gastric cancer, radical surgery is only carried out if there is no extensive nodal involvement at the time of surgical exploration. Both postoperative chemoradiation (for stages I through III disease) and neoadjuvant therapy (for stages II and III disease) can be considered because there is a proven survival benefit.⁵ For patients with stage IV cancer, palliative chemotherapy, radiotherapy, or resection might be appropriate.

Colorectal cancer is the third most common cancer worldwide in men and second most common in women, with the highest incidence in Australia, New Zealand, Europe, and North America. Risk factors include a diet rich in red and processed meat but low in fiber, obesity, smoking, alcohol consumption, inflammatory bowel disease, and polyposis syndromes. Greater than 90% of cases are adenocarcinomas. It is thought that at least 70% of tumors follow transformation of a benign adenoma into a carcinoma via a multistep accumulation of genetic faults (the adenoma to carcinoma sequence), with the remaining 30% of tumors arising de novo from normal mucosa. The risk of malignant transformation of an adenoma is related to its size, with adenomas greater than 1 cm in size posing a greater risk. Five-year survival rates for colorectal cancer have doubled between the early 1970s and
mid-2000s,^6,7 related to improvements in surgical and radiotherapy techniques and the introduction of novel chemotherapeutic (including targeted) agents. Surgical resection is carried out in the majority of patients, although up to a third of colorectal cancer cases will relapse, usually within 3 years.^8,9,10 In order to reduce recurrence, total mesorectal excision is now routinely used for middle and lower third rectal cancers. Prognosis is related to tumor stage at presentation, with 80% 5-year survival rate in patients with Dukes stage A cancers, but 35% for Dukes stage C tumors.

Postoperative chemotherapy is given to patients with Dukes stage C colon cancer and might be appropriate for patients with Dukes stage B cancer, although this remains controversial. This usually consists of 5-fluorouracil and folinic acid (with or without irinotecan and oxaliplatin). To date, chemotherapy has made little impact on the survival of patients with advanced cancer, with only a 5% to 10% improvement.^11,12 In the United Kingdom, in locally advanced rectal cancer (stage T3b or greater, where the circumferential resection margin is at risk), neoadjuvant chemoradiotherapy is given prior to surgery to increase the rate of R0 resections and to reduce the risk of local recurrence. Patients with advanced colorectal cancer are treated with palliative chemotherapy or radiotherapy. Newer targeted therapies (e.g., anti–vascular endothelial growth factor [VEGF] agents), have been shown to improve survival in the metastatic setting.

Crohn disease is a chronic transmural granulomatous inflammatory disorder of the bowel of unknown pathogenesis. The most common site of disease is the terminal ileum, but any site within the gastrointestinal tract can be affected. Typically there are discontinuous “skip” lesions with asymmetrical bowel wall involvement. Other features include bowel wall thickening and ulceration, strictures and stenoses, fistulae formation and mesenteric hypervascularity, and fibrofatty proliferation. In addition to dietary measures, several drugs can be used to induce or maintain remission in active disease (e.g., steroids and immunomodulators). Antitumor necrosis factor alpha antibodies (e.g., infliximab, adalimumab) have become an established and highly effective therapy for moderate to severe Crohn disease. Surgical resection and diversion may be required in those patients who develop complications arising from penetrating disease or obstructive symptoms from fibrotic strictures.

Diverticulitis is the most common complication associated with the presence of diverticulosis, affecting 10% of patients that have diverticulosis. Diverticulosis is most common in the sigmoid colon. Diverticulitis follows the stagnation of fecal material within the diverticulum, with associated inflammatory erosion of the mucosal lining of the diverticulum and leading potentially to perforation and intramural or extramural abscess formation. Fistulae and sinus formation are additional possible sequelae. A high fiber diet may help relieve symptoms in simple diverticular disease. If diverticulitis arises, mild symptoms may response to antibiotics and liquid diet. If complications develop, such as abscess or fistula formation, then percutaneous drainage or surgical resection may be required.