27. | Principles of Surgery, Companion Handbook

Chapter 26 Colon, Rectum, And Anus

Principles of Surgery Companion Handbook

CHAPTER

26
COLON, RECTUM, AND ANUS

Anatomy
	Colon
	Rectum and Anus
Physiology
	Normal Colonic Function
Disorders of Colonic Motility
	Normal Function of the Anorectum
	Dysfunction of the Anorectum
Diagnostic Tests in Colon and Rectal Disease
Diverticular Disease
	Diverticulitis
	Bleeding from Diverticular Disease and Angiodysplasia
Infections
	Infectious Colitides
	Infections of the Anorectal Region
Inflammatory Bowel Disease
	Medical Treatment of Inflammatory Bowel Disease
	Ulcerative Colitis
	Crohn's Disease
Neoplastic Disease
	Etiology
	Screening for Polyps and Cancer
	Polyps
	Large Bowel Cancer
	Other Colorectal Tumors
	Anal Neoplasms
Miscellaneous Lesions
	Colonic Pseudo-Obstruction (Ogilvie's Syndrome)
	Volvulus
	Ischemic Colitis
	Radiation Proctitis
	Rectal Prolapse
	Anal Fissure
	Rectovaginal Fistula
	Pruritus Ani
	Hemorrhoids

ANATOMY

Colon

Structure The colon is 90–150 cm. Its diameter varies. The cecum is the widest part (7.5–8.5 cm), and the sigmoid colon is the narrowest (2.5 cm). In cases of distal obstruction, the cecum is the part most likely to rupture (Laplace's law: T = P ´ R). The layers of the colonic wall include mucosa, submucosa, circular muscle, longitudinal muscle that coalesces into three separate teniae coli, and serosa. The mechanical strength of the colonic wall derives from the submucosa, the layer with the highest collagen content. The ascending colon and descending colon usually are fixed to the retroperitoneum, whereas the cecum, transverse colon, and sigmoid colon usually are intraperitoneal and mobile. The omentum is attached to the transverse colon.

Arterial Supply The superior mesenteric artery supplies the ascending colon and transverse colon through its ileocolic artery, right colic artery (present in only 15 percent of patients), and middle colic artery. The inferior mesenteric artery supplies the descending colon and sigmoid colon through its left colic branch and sigmoidal branches.

Venous Drainage The inferior mesenteric vein drains the descending colon, sigmoid colon, and upper part of the rectum and enters the splenic vein. The rest of the venous drainage of the colon follows the arterial pattern and joins the superior mesenteric vein.

Lymphatic Drainage Lymphatic drainage originates in the submucosa and follows the arterial supply.

Nerve Supply The sympathetic nerves usually inhibit peristalsis, and the parasympathetic nerves stimulate it. The sympathetic supply to the colon is derived from the thoracolumbar segments. The parasympathetic supply to the ascending colon and transverse colon is derived from the posterior vagus nerve and to the descending colon and sigmoid colon from the S2–S4 sacral roots.

Rectum and Anus

Structure The teniae coli end at the distal sigmoid colon, and the longitudinal muscle layer of the rectal wall is continuous. The rectum is 12–15 cm long, extending from the sigmoid colon to the anal canal. The anterior peritoneal reflection is 5–9 cm from the anal verge and usually is larger in males. In its upper part, the rectum is covered with peritoneum anteriorly, and in its lower part, it is extraperitoneal. There are three lateral curves in the rectum that form the valves of Houston. The rectum is surrounded by extensions of the pelvic fascia, which have to be divided during surgical dissection.

The pelvic floor is formed by the levator ani muscle. The anal canal is about 4 cm long, extending from the pelvic floor to the anal verge. The dentate line is the mucocutaneous junction, about 1.5 cm from the anal verge. The anal canal is surrounded by the anal sphincter, which has an internal and external component. The internal sphincter is a continuation of the circular smooth muscle of the rectum, is an involuntary muscle, and is normally contracted at rest. The external sphincter is a voluntary striated muscle and is a caudad extension of the levator ani.

Arterial Supply The upper part of the rectum is supplied by the superior rectal artery, which is the terminal branch of the inferior mesenteric artery. The lower part of the rectum is supplied by the middle rectal and inferior rectal arteries, which are branches of the internal iliac arteries.

Venous Drainage This corresponds to the arterial supply, with the upper part of the rectum draining into the inferior mesenteric vein and the lower part into the caval system through the internal iliac veins. The two parts are connected by a rich network of collaterals, and therefore, low rectal and anal canal tumor can metastasize to both the portal and systemic venous systems.

Lymphatic Drainage This follows the arterial supply. The upper rectum drains into the inferior mesenteric lymph nodes. The lower rectum may drain into the inferior mesenteric system or the iliac lymph nodes. Below the dentate line the drainage is to the inguinal lymph nodes.

Nerve Supply The sympathetic innervation of the rectum as well as the bladder and the genital system is from the hypogastric nerves originating in the thoracolumbar segments. The parasympathetic supply is from the nervi erigentes (S2–S4 sacral roots). Injury to these nerves during surgical dissection can cause bladder and sexual dysfunction. The sympathetic system usually controls ejaculation, and the parasympathetic controls erection.

PHYSIOLOGY

Normal Colonic Function

The colon absorbs water, sodium, chloride, and short-chain fatty acids and secretes potassium and bicarbonate. It helps in maintaining fluid balance and avoiding dehydration. This capacity is lost in patients with an ileostomy, who are more prone to dehydration.

Colonic Motility This is complex and not fully understood. Three patterns of colonic contraction are observed on radiologic studies: retrograde movements, segmental contractions, and mass movements. The latter cause propagation of colonic contents toward the anus. Colonic motility is influenced by emotions, hormones, and the amount of bulk in the diet.

Colonic Flora Bacteria account for one-third of the weight of the feces. There are 10¹¹ to 10¹² bacteria per gram of feces. Bacteroides species, an anaerobe, is the most common. Escherichia coli and other enterobacteria are the common aerobes, 10⁸ to 10¹⁰ organisms per gram. Colonic bacteria are important in the production of vitamin K. Suppression of the normal flora with broad-spectrum antibiotics may lead to overgrowth of pathogens, specifically Clostridium difficile.

Colonic Gas Ninety-nine percent of colonic gas is nitrogen, oxygen, carbon dioxide, hydrogen, and methane. The gas in the bowel is derived from swallowed air, bacterial fermentation of carbohydrates and protein in the bowel lumen, and diffusion to the bowel lumen from the blood. The average daily flatus volume is 600 cc. Hydrogen and methane are combustible, and accordingly, electrosurgery should not be performed on unprepared bowel. Complaints of excessive bowel gas may be improved by diet modifications.

DISORDERS OF COLONIC MOTILITY

Irritable Bowel Syndrome This is the most common cause of chronic abdominal pain. It is manifest by alternating constipation and diarrhea, pain, and bloating. Workup for organic causes of pain is negative. Treatment includes reassurance, diet modifications, and antispasmodic medications.

Constipation This usually is defined as less than three bowel movements per week while on a high-residue diet. Causes include neoplasms, metabolic and endocrine disorders (hypothyroidism), neurologic diseases (Parkinson's disease), medications (narcotics, antidepressants), a low-fiber diet, colonic inertia with slow transit, and anomalies of the pelvic floor. A recent onset of constipation is an indication to study the colon for neoplasms. Slow colonic transit is evaluated by ingestion of radiopaque markers that are followed throughout the gastrointestinal (GI) tract with serial abdominal radiographs. Pelvic floor anomalies are evaluated by anal manometry and defecography (see below). In patients with colonic inertia documented by transit time study and normal pelvic floor function who do not respond to conservative treatment, surgical treatment with abdominal colectomy and ileorectal anastomosis should be considered.

Normal Function of the Anorectum

The rectum functions mainly as a reservoir and holds up to 1200 cc of liquid. The anal sphincter has an external component that provides the voluntary squeeze pressure and an internal component that provides the resting pressure. Continence is defined as controlled elimination of rectal contents. Defecation has the following stages:

Movement of feces into the rectum
Rectal-anal inhibitory reflex in which distention of the rectum causes relaxation of the internal anal sphincter
Voluntary relaxation of the external anal sphincter
Voluntary increase of intraabdominal pressure by the diaphragm and abdominal wall muscles, causing evacuation of feces through the anal canal

Dysfunction of the Anorectum

Incontinence This is defined as an inability to control rectal evacuation. The cause may be mechanical (such as damage to the sphincter during birth trauma) or neurogenic (diabetic neuropathy, multiple sclerosis). Evaluation of incontinence includes

Digital examination to assess the anatomy of the anal sphincter
Anal manometry assessing resting pressure, squeeze pressure, and sensation
Pudendal nerve terminal motor latency, which assesses velocity of conduction in the pudendal nerve
External sphincter electromyography
Endorectal ultrasound to assess integrity of the anal sphincter

Surgical correction of mechanical incontinence is aimed at restoring the circular integrity of the sphincter mechanism. In patients with extensive injury to the sphincter muscle and nerves, precluding sphincter repair, reconstruction may be done by encircling the rectum with a flap of gracilis or gluteus maximus muscle. Modest success is reported.

Obstructed Defecation This refers to deficient relaxation of the anal sphincter, specifically the puborectalis, on attempting defecation. Diagnosis is established by defecography, in which barium with stool consistency is installed in the rectum, and defecation attempts are documented on cinefluoroscopy.

DIAGNOSTIC TESTS IN COLON AND RECTAL DISEASE

The rectal examination is mandatory. The examining finger reaches about 8 cm above the dentate line and can detect distal rectal cancers and polyps, palpate prostatic nodules, detect neoplastic and inflammatory lesions in the cul-de-sac, assess the tone and integrity of the anal sphincter, and obtain stool for occult blood testing.

Tests for Occult Blood These are based on the peroxidase activity of blood, which creates a blue color reaction with guaiac gum by adding hydrogen peroxide. The false-positive rate is high because of other catalysts in the diet that produce the same reaction, as well as bleeding from other trivial sources in the GI tract not related to malignancy. Cancer also may bleed intermittently; occult blood tests might be negative in patients with malignancy. Despite this, occult blood testing of the stool is considered a standard test and has been proved to decrease mortality from colon cancer.

Carcinoembryonic Antigen (CEA) This glycoprotein is present in colorectal cancer and serves as biochemical marker for the malignancy. Its serum level is elevated in advanced and metastatic disease but usually is normal with localized disease. It also is elevated in other malignancies (e.g., breast, pancreas) and in ulcerative colitis, cirrhosis, and renal failure. It is nonspecific and not sensitive enough for screening purposes. Its main clinical use is for follow-up after operation. Serial elevations suggest recurrent or metastatic disease.

Endoscopic Tests Rigid Proctosigmoidoscopy The rigid sigmoidoscope is 25 cm long and 2 cm in diameter with an attached light source. The examination usually reaches 15 cm. Beyond this level it may cause significant discomfort to the patient. This is a good, simple, and inexpensive tool to fully assess the rectum, obtain biopsies, and remove small polyps. It can be done easily in an office setting. The preparation for the test is by administration of two Fleet enemas. A suction device is necessary.

Flexible Sigmoidoscopy The instrument is 60 cm long and uses fiberoptic or video technology. The examination usually reaches the middle descending colon and will detect up to 50 percent of large bowel malignancies. It is the standard screening tool for large bowel neoplasms in average-risk patients over age 50.

Colonoscopy The test allows visualization of the large bowel and the terminal ileum. The original technology was fiberoptic, but this has been largely replaced by video technology, which allows higher-resolution images, convenience for the examiner, and improved participation of the assistant staff. It is the most accurate tool in detecting colonic neoplasms, and it allows biopsy, removal of polyps, as well as control of large bowel bleeding; it usually is preferable to barium enema. The test requires good bowel preparation, similar to that of colon resection, and usually is done with intravenous sedation (“conscious sedation”) on an outpatient basis. Complications, which are uncommon, include perforation and bleeding.

Imaging Techniques Contrast Studies The standard test is an air contrast (“double contrast”) barium enema (BE), which has good sensitivity in detecting malignancies and polyps larger than 1 cm. The older “full column” barium enema is used less commonly because of lower sensitivity. Barium should be avoided in acutely ill patients, in whom peritonitis or perforation is a concern, as well as in patients who are likely to need colonoscopy or computed tomographic (CT) scan of the abdomen, because the presence of barium in the bowel interferes with these tests. Water-soluble contrast material (Hypaque, Gastrografin) is preferable in these situations.

Computed Tomographic (CT) Scan This is an excellent tool in assessing infectious processes like diverticulitis and abscesses. And it is a standard test in assessing liver metastases from colon cancer.

Magnetic Resonance Imaging (MRI) Unlike the CT scan, in MRI there is no need for intravenous contrast material, and the test can be used safely in patients with renal failure and in those with allergy to contrast material.

Endorectal Ultrasound This is performed by inserting an ultrasound probe into the rectum. It is sensitive and accurate in assessing the depth of invasion of rectal cancer and lymph node involvement. It also is useful in assessing the anatomy of the anal sphincter and a perianal infectious process.

DIVERTICULAR DISEASE

Colonic diverticula are false, since their wall does not contain a muscle layer. The incidence of diverticulosis increases with age and is estimated to be 75 percent in Americans over age 80. Diverticulosis is attributed to the Western diet, which is low in dietary fiber. A possible mechanism of diverticular formation is increased intraluminal pressure causing herniation of the submucosa through weak areas in the colonic wall, usually at a site where an arteriole penetrates the wall. The part of the large bowel most affected is the sigmoid colon. Diverticulosis has the potential for complications but by itself is usually not associated with symptoms and could barely be considered a pathologic finding.

Diverticulitis

Diverticulitis is an inflammation starting in a diverticulum and affecting the tissues around the bowel wall; usually it is associated with perforation in the wall of the diverticulum. The part of the colon most often affected is the sigmoid (“left-sided appendicitis”). Patients with acute diverticulitis present with left lower quadrant pain, change in bowel habits, fever, localized tenderness, left lower quadrant mass, possible distention as a result of partial obstruction or ileus, pelvic tenderness on rectal examination, and leukocytosis. Diagnosis can be verified by CT scan of the abdomen showing inflammatory changes in the pericolic and mesenteric fat or with a water-soluble contrast study showing an extramucosal mass effect. If an abscess is seen on CT scan, percutaneous drainage under CT guidance can be done. Barium studies are undesirable in the acute stage of the disease.

Treatment Uncomplicated diverticulitis often can be treated on an outpatient basis with a clear liquid diet and broad-spectrum antibiotics by mouth (a combination of metronidazole and ciprofloxacin is safe and effective). Sicker patients should be hospitalized and treated with intravenous antibiotics and bowel rest. Most patients respond to conservative treatment within 48 h.

In patients with recurrent attacks of diverticulitis or those who do not respond to medical treatment, surgery may be indicated. When surgery is performed electively with adequate antibiotic and mechanical bowel preparation, a primary anastomosis is constructed after resecting the involved segment.

In patients who present with free perforation and peritonitis, urgent surgery is necessary for sepsis control, which obviously does not allow for mechanical cleansing of the bowel. The involved segment of the colon, usually the sigmoid colon, is resected, the distal segment is closed as a blind pouch, and the proximal bowel is brought to the skin level as an end-colostomy (Hartmann's procedure). In experienced hands and with good-risk patients, primary anastomosis without a colostomy may still be considered. In patients who present originally with diverticular abscess, CT-guided percutaneous drainage may provide control of the acute sepsis and enable elective colon resection later.

Diverticulitis can cause fistulization between the sigmoid colon and adjacent organs, including the urinary bladder, vagina, and small bowel. A colovesical fistula will manifest with pneumaturia and recurrent urinary tract infections. Surgical treatment is resection of the involved colonic segment.

Bleeding from Diverticular Disease and Angiodysplasia

Because of the proximity of the diverticula to the colonic arterioles, erosion in the wall of the diverticulum may involve the arterial wall. The bleeding is painless, often massive, and may cause hypovolemic shock.

This primarily affects older patients. The two most common causes are diverticulosis and angiodysplasia. With angiography readily available, angiodysplastic lesions of the colon and the rest of the GI tract are frequently diagnosed. These lesions are acquired, occur in elderly people, and more commonly are localized in the right colon. An angiogram will show the site of the bleeding and the presence of an early filling vein resulting from arterial venous shunting within the lesion. Larger lesions can be detected colonoscopically.

Massive lower GI bleeding is defined as bleeding from a source distal to the ligament of Treitz that exceeds 3 units of blood in 24 h. Inflammatory bowel disease, ischemic colitis, and tumors may cause lower GI bleeding, but this rarely is massive or life threatening. With significant rectal bleeding, it is important to rule out a gastroduodenal source by placement of a nasogastric (NG) tube or, preferably, by esophagogastroduodenoscopy. Initial management includes volume resuscitation, correcting coagulopathy if present, and attempts to identify the source of bleeding. Diagnostic tests include proctoscopy to rule out an anorectal source, a tagged red blood cell scan, mesenteric angiography, and colonoscopy. The tests supplement each other, and the choice of the specific test depends on the clinical circumstances and the expertise of the examiner.

Between 75 and 90 percent of lower GI bleeding will stop without surgery. In the remaining patients, surgery is necessary to control bleeding. If the source of bleeding is definitely identified, segmental resection is performed. Otherwise, after ruling out bleeding from the small bowel and rectum, abdominal colectomy with ileostomy or with ileorectal anastomosis is performed.

INFECTIONS

Infectious Colitides

Bacterial Colitis Causative organisms include Campylobacter, pathogenic E. coli, Salmonella, and Shigella. The clinical presentation is that of acute diarrheal disease, sometimes bloody. Diagnosis is obtained by stool cultures and stool analysis for leukocytes. Most organisms are sensitive to aminoquinolines (e.g., ciprofloxacin).

Pseudomembranous Colitis This occurs in patients who received broad-spectrum antibiotics (e.g., clindamycin, semisynthetic penicillins, cephalosporins). Alteration of the normal colonic flora results in overgrowth of C. difficile, an anaerobe that produces an exotoxin that injures the colonic mucosa. This syndrome can occur up to 6 weeks after antibiotic therapy. The clinical spectrum varies from mild self-limited diarrhea to severe transmural inflammation, toxic colon, and perforation. Leukocytosis is out of proportion to the other clinical findings. Diagnosis is established by checking the stool for the toxin and endoscopy that may show the typical yellowish pseudomembranes. Treatment includes stopping the antibiotics, if possible, and metronidazole PO or IV. Vancomycin is an alternative treatment but is avoided, if possible, because of the risk of emergence of vancomycin-resistant Enterococcus. Patients with toxic colon or perforation may need resection. The recurrence rate after conclusion of treatment is about 20 percent.

Amebic Colitis The infection is caused by the protozoan Entamoeba histolytica, usually involves the colon, and may spread secondarily to the liver as an amebic abscess. Most patients are asymptomatic carriers. Active disease manifests with multiple small ulcers throughout the colon but mainly in the cecum.

The clinical presentation is that of bloody diarrhea that may imitate ulcerative colitis. Complications include toxic colon, perforation, and development of cecal ameboma that may imitate cancer. Diagnosis is established by stool analysis of a fresh specimen. Treatment is metronidazole and Iodoquinol.

Cytomegalovirus (CMV) Colitis This occurs mainly in acquired immune-deficiency syndrome (AIDS) patients. Ten percent of these patients will develop CMV colitis with mucosal ulceration, diarrhea, hemorrhage, fever, and weight loss. Endoscopic biopsy may be diagnostic. The treatment is ganciclovir.

Infections of the Anorectal Region

ABSCESS AND FISTULA

Fistulas are the result of abscesses draining to the surface. Most abscesses originate in the anal glands, at the level of the dentate line. From there they may spread to different anatomic locations: the intersphincteric plane between the internal and external sphincters, the perianal space adjacent to the anus, the ischiorectal space between the rectum and the ischial tuberosity, or the supralevator space above the levator ani.

The main symptom is severe throbbing anal pain, typically keeping the patient awake at night. The examination reveals swelling and tenderness in the perianal area. If the abscess is intersphincteric, it may be detected only by rectal examination and may not be visible on the outside. The treatment is surgical drainage. Antibiotics are added to patients with extensive infection, have a high fever, or are immunocompromised. An intersphincteric abscess is drained through the anal canal by dividing the overlying mucosa and internal sphincter.

Fifty percent of patients treated by drainage will be cured. The other 50 percent will develop an additional abscess or a perianal fistula connecting the anal canal, usually at the level of the dentate line, to the perianal skin. Treatment of fistula is by fistulotomy, laying the tract open. If the fistula tract incorporates a significant part of the sphincter, fistulotomy may result in incontinence. An alternative treatment may be encircling the involved tissue with heavy silk thread or a rubber band (seton), which provides drainage and stimulates scarring. The seton can be removed later or allowed to gradually cut through the tissue it incorporates while scar formation is progressing, and a gap in the sphincter continuity is avoided.

PILONIDAL DISEASE

This is a sinus or abscess cavity in the sacrococcygeal area resulting from ingrowth of hair. It is most common in the second and third decades of life, with a male predominance. The primary opening is usually at the intergluteal crease in the midline, about 5 cm above the anus. The acute presentation is that of a painful abscess. After it resolves, a chronically infected and draining sinus remain. Identifying the typical midline pits makes the diagnosis. Surgical treatment includes unroofing and drainage of the sinus, but the primary openings have to be excised to prevent recurrence.

HIDRADENITIS SUPPURATIVA

This infection affects the apocrine sweat gland in the perianal region, with superficial sinuses and abscesses involving the dermis and subcutaneous tissue. Treatment is by wide drainage of the infected sinuses.

NECROTIZING PERINEAL INFECTIONS (FOURNIER'S GANGRENE)

This often occurs in compromised hosts (e.g., AIDS patients, diabetics, or those on chemotherapy), but sometimes without an obvious underlying illness, trivial infections of the perianal region or to the lower urogenital tract may develop into an aggressive, life-threatening soft tissue infection. The presenting picture is that of severe perineal pain, swelling, fever, leukocytosis, and gangrene of the soft tissue of the perineum. The infection usually is polymicrobial and synergistic. Treatment includes broad-spectrum antibiotics, aggressive debridement to the level of viable tissue, which may include excision of the scrotal skin, and sometimes a diverting colostomy.

SEXUALLY TRANSMITTED DISEASES OF THE ANORECTUM

These usually are transmitted by anal intercourse and are more common in male homosexuals. Infected vaginal discharge can transfer the disease to the anal area in females. Diagnosis is obtained by specific cultures and serologic tests, and treatment is with the appropriate antimicrobial agents. Conditions include gonococcal proctitis, anorectal syphilis, chlamydial proctitis, herpes proctitis, and anal warts.

Anal warts, or condylomata acuminata, are caused by human papillomavirus (HPV). HPV infections are the most common sexually transmitted diseases in Western countries. The lesions may be external, on the perineal skin, or internal, within the anal canal.

Diagnosis is made by the characteristic appearance and by histologic examination of removed specimens. Treatment is by surgical excision and fulguration or by application of a variety of local preparations. The recurrence rate is high in all techniques used because of residual virus in the tissue, although surgical excision has the highest success rate. Certain serotypes of the papillomavirus are associated with malignant degeneration to squamous cell carcinoma, and accordingly, lifelong follow-up is recommended. Since a sexual contact can transmit more than one type of infection at a time, these patients also should be tested for infection with the human immunodeficiency virus (HIV), hepatitis B, hepatitis C, syphilis, gonorrhea, and chlamydia.

INFLAMMATORY BOWEL DISEASE

This includes two major entities, ulcerative colitis (UC) and Crohn's disease (CD). The two conditions are closely related and are attributed to a defect in immune regulation in the GI tract that leads to uncontrolled immune reaction to different antigens. Ulcerative colitis usually is confined to the large bowel, involving the mucosa (termed mucosal colitis), whereas Crohn's disease may affect any part of the GI tract, from the mouth to the anus, and usually involves the full thickness of the bowel wall. The clinical pictures overlap, and in 15 percent of patients the colitis is indeterminate. Symptoms usually are related to inflammation of the bowel and include diarrhea, rectal bleeding, tenesmus, abdominal pain, fever, and weight loss. Other organs may be affected, including the musculoskeletal system (spondylitis, arthritis), the skin (erythema nodosum, pyoderma gangrenosum), the eye (iritis), the hematopoietic system (anemia, thrombocytosis, hypercoagulable state), the kidneys (nephrolithiasis), and the biliary tract (sclerosing cholangitis, cholelithiasis).

Differences between the two entities include the fact that CD may affect any part of the GI tract, and in most patients the small bowel is involved, often in a noncontinuous distribution (“skipped” segments), whereas UC is usually continuous from the rectum proximally and usually involves the colon only and at the most the very distal part of the ileum (“backwash” ileitis); fistulas are rare in UC and common in CD; strictures are common in CD and rare in UC; perianal disease (fistulas, abscesses, fissures) are common in CD and uncommon in UC; and the malignant potential is higher in UC than in CD.

The clinical presentation depends on the extent of involvement, severity of the inflammation, and chronicity. The most acute presentation is that of toxic colon (not necessarily “megacolon”) requiring aggressive medical management and often necessitating colectomy.

A milder form of ulcerative colitis may involve the distal large bowel, the rectum, or the rectum and the sigmoid colon. It is called ulcerative proctitis or ulcerative proctosigmoiditis. Ninety percent of these patients respond to medical treatment and never go on to develop pancolitis.

Medical Treatment of Inflammatory Bowel Disease

This is similar for ulcerative colitis and Crohn's disease, suggesting a like etiology. Sulfasalazine, the former mainstay of therapy, has been largely replaced by 5-aminosalicylic acid (5-ASA) preparations (Asacol, Pentasa), which have much fewer side effects and are better tolerated by patients. These are maintenance medications for stable ulcerative colitis and Crohn's colitis.

In acutely ill patients on initial presentation or in previously diagnosed patients with a flare-up, the acute stage is controlled with steroids, usually prednisone, in doses of 20–80 mg/day, with quick tapering of the dose on clinical response. The most severely ill patients may require hospitalization, intravenous fluids, bowel rest, and intravenous steroids. If there is no response to medical treatment within a few days, operation is performed usually by abdominal colectomy.

The role of immunomodulators (previously called immunosuppressants), such as 6-mercaptopurin (6MP) and Imuran, is gradually increasing as their efficacy and safety become better established. They are used mainly for maintenance therapy and as steroid-sparing drugs in patients who remain significantly symptomatic while on 5-ASA preparations alone. Side effects include bone marrow suppression, pancreatitis, and the theoretical concern of inducing malignancies, especially lymphomas. In long-term use, 6MP is better tolerated than prednisone and has fewer side effects.

Success has been reported in the use of short courses of cyclosporin A given intravenously to control acute colitis not responsive to steroids. The use of antibiotics has been studied extensively. The only one with proved efficacy is metronidazole for perianal Crohn's disease and in controlling abscesses and fistulas. In 1998 the Food and Drug Administration (FDA) approved a new drug, infliximab, a chimeric monoclonal antibody to tumor necrosing factor (TNF), for use in Crohn's disease resistant to other treatment.

Ulcerative Colitis

Indications for Surgery Indications include active disease not responsive to medical therapy, uncontrolled bleeding, toxic colon not responsive to aggressive medical treatment, and risk of malignancy. In patients with ulcerative colitis for more than 7 years, colonoscopic surveillance is recommended every 1–2 years with multiple random biopsies. A finding of mucosal dysplasia is an indication for operative removal of the large bowel.

Surgical Management Because inflammation is confined to the large bowel, resection of this organ is curative, unlike Crohn's disease, which cannot be eradicated surgically and has a high risk of recurrence after resection. For decades, the operation of choice was total proctocolectomy with ileostomy. In the last 20 years, a sphincter-sparing operation evolved, restorative proctocolectomy. This involves resection of the colon and upper rectum, removal of the mucosa of the remaining rectum, constructing an ileal reservoir (pouch) from the terminal ileum, and anastomosing the reservoir at the level of the dentate line. The operation removes all large bowel mucosa while preserving the sphincter mechanism and maintaining continence. Candidates for this operation are younger patients, usually under 50 years of age, with adequate sphincter function and in whom Crohn's disease has been ruled out. They are willing to accept problems associated with the pouch, including the potential for mild incontinence, multiple bowel movements a day, and the potential for recurrent episodes of pouch inflammation (“pouchitis”).

Crohn's Disease

Unlike ulcerative colitis, surgery is not curative, and recurrence rates are high. Surgery is indicated only for complications that do not respond to conservative treatment. Surgical treatment of Crohn's disease usually involves resection of the diseased segment of the bowel. When the presentation is acute with localized perforation, abscess, or phlegmon, it is desirable to control the acute complications nonsurgically and perform the operation on a less urgent basis.

Ileocolonic Crohn's Disease This variant involves the ileocecal area. It may present with obstruction, internal fistulization, or abscess formation. It is desirable to drain the abscesses percutaneously before operative resection.

Colonic Crohn's Disease Presentation is similar to that of ulcerative colitis, including toxic colon. Surgical options include total proctocolectomy with ileostomy or, in patients with relative rectal sparing, an abdominal colectomy with ileorectal anastomosis. Restorative proctocolectomy should not be done.

Anorectal Crohn's Disease This may manifest with bleeding, tenesmus, multiple abscesses and fistula formation, and loss of the reservoir capacity of the rectum due to scarring, leading to frequent bowel movement. In 35 percent of patients with Crohn's disease, the anus is involved, and in 4 percent, anal involvement is the first manifestation of the disease. Surgery for complications such as abscess and fistula should be as conservative as possible, avoiding cutting any part of the anal sphincter because of the poor healing of wounds and the risk of incontinence.

NEOPLASTIC DISEASE

The two most significant neoplastic lesions of the large bowel are adenoma, or adenomatous polyp, and adenocarcinoma. It usually is accepted that the two are related, representing different stages of the same process, and that most cancers are derived from adenomatous polyps, hence the adenoma-carcinoma or polyp-cancer sequence. Carcinoma arising de novo from flat colonic mucosa is much less frequent. One major exception is the cancer arising from dysplastic mucosa in inflammatory bowel disease, in which there is no “polyp stage.” Accordingly, discussions regarding etiology and screening refer to both adenomatous polyps and cancer.

Etiology

The exact etiology is not known, but it is recognized that neoplastic proliferation of the large bowel mucosa is related to alterations in the genetic code, either in the germ line or as an acquired somatic mutation.

Genetic Considerations It is estimated that 10–15 percent of colorectal cancer cases are familial.

Familial Adenomatous Polyposis (FAP) An autosomal dominant disorder, the diagnosis requires the presence of more than 100 polyps in the large bowel. The polyps are adenomatous, and the process leading to malignancy follows the adenoma-carcinoma sequence. Extracolonic manifestations include desmoid tumors in the abdomen, osteomata, and adenomata of the stomach and duodenum. All patients will develop cancer, usually by age 40, unless treated surgically. In the past these patients were treated with abdominal colectomy and ileorectal anastomosis, necessitating continuous surveillance of the rectal mucosa for the development of polyps and malignancy, or with total proctocolectomy with ileostomy. These procedures have been largely replaced with restorative proctocolectomy.

Hereditary Nonpolyposis Colorectal Cancer (Lynch Syndrome) The criteria for this syndrome include

At least three relatives with colorectal cancer, two of which are first degree
Involvement of at least two generations
At least one patient diagnosed under the age of 50.

The syndrome is characterized by autosomal dominant inheritance, early age at the manifestation of malignancy, predominance of lesions in the proximal colon, and tendency for synchronous and metachronous lesions. Accordingly, it is recommended that patients be treated with subtotal colectomy. A few different DNA defects were identified in this syndrome. The cancer develops from adenomatous polyps through the typical adenoma-carcinoma progression. In a variant of the syndrome there is an increased incidence of endometrial, gastric, ovarian, and urinary malignancies.

Dietary Factors Epidemiologic studies indicate that diet has a role in the development of colon cancer. In third world countries where diets include less processed food and are higher in fiber and lower in fat, the incidence of colorectal cancer is lower. When people from these countries immigrate to the United States, they acquire a higher rate of colon cancer. Dietary recommendations include decreasing the fat content and increasing the fiber in the diet.

Chronic Inflammation Inflammatory bowel disease, especially chronic ulcerative colitis, is associated with an increased risk of colon cancer. Early age of onset, involvement of the whole colon, and more than 10 years of the illness indicate high risk for malignancies. For patients with pancolitis for 25 years, the risk of cancer is estimated to be 40 percent. Accordingly, surveillance colonoscopy is recommended in patients with pancolitis starting at 7–10 years from onset and performed once a year. Multiple biopsies are obtained, and a finding of dysplasia indicates a possible need for operation.

Screening for Polyps and Cancer

Screening is aimed at the general population with average risk of large bowel cancer. The goal is to detect a neoplastic process at an early stage, ideally at the polyp phase of the polyp-cancer sequence. Complex considerations regarding cost-effectiveness, reliability, sensitivity, and specificity all affect the choice of the screening test. Current recommendations are that average-risk patients over age 50 will have yearly fecal occult blood testing and flexible sigmoidoscopy every 5 years. If the occult blood testing is positive, or if polyps are found on sigmoidoscopy, pancolonoscopy is indicated. In individuals with a history of polyps, previous large bowel cancer, family history of colon cancer, or ulcerative colitis for more than 10 years, periodic colonoscopy is recommended. The interval depends on the specific clinical situation and usually is every 5 years.

Polyps

There are three histologic types: hamartomas, hyperplastic polyps, and adenomas. The latter is a true neoplasm with the most clinical significance.

Hamartomas A hamartoma is a growth showing excessive proliferation of one type of tissue without true neoplastic changes.

Peutz-Jeghers Syndrome This is an autosomal dominant syndrome manifested with pigmentation of the mucocutaneous areas and hamartomous polyps of the small and large bowel composed of excessive amounts of muscularis mucosa. Progression of the polyps to malignancy has been described but is not common. There is a higher incidence of malignancy in other organs, including breast and ovary. Symptoms include bleeding and bowel obstruction secondary to intussusception.

Juvenile Polyps These usually occur in children but are seen in adults as well. They are hamartomas composed of dilated glands and abnormal lamina propria. Bleeding secondary to autoamputation or intussusception can occur.

Familial Juvenile Polyposis This is an autosomal dominant syndrome with multiple juvenile polyps throughout the colon. It can manifest with bleeding or obstruction, and there is increased risk of GI malignancies. The treatment is subtotal colectomy.

Hyperplastic Polyps These are very common, usually less than 5 mm in size, with histologic examination showing no maturation and hyperplasia without nuclear dysplasia. They are not considered premalignant.

Adenomatous Polyps These are the most significant polyps because of frequency and malignant potential. Some will develop to cancer, a process that may take 5–15 years. Morphologically, these polyps are described as pedunculated (with a stalk) or sessile (flat). Histologically, they are classified as tubular, villous, or mixed tubulovillous depending on the dominant pattern. The bigger the polyp, and the more villous component it has, the more the malignant potential.

Most benign polyps are asymptomatic. Occasionally, large pedunculated polyps can manifest with bleeding or intussusception. As a general rule, adenomatous polyps should be removed because of their malignant potential. Most polyps can be removed by colonoscopic snaring, usually in one piece. Large or sessile polyps may necessitate piecemeal polypectomy, in one or more sessions. Occasionally, in patients who are good surgical risks with a long life expectancy, large or sessile polyps that cannot be completely or safely removed by colonoscopic snaring may require colectomy.

Malignant polyps are those in which neoplastic changes proceed deep to the muscularis mucosa. For these, polypectomy may still be a sufficient treatment if the following criteria are fulfilled:

The polyp is pedunculated.
The stalk is not involved, and the margins of resection are free.
There is no vascular, lymphatic, or neural invasion, and the lesion is not poorly differentiated.

Large Bowel Cancer

This is the most common cancer of the GI tract. In women it is second only to breast cancer as a cause of cancer-related death, and in men it is third after carcinoma of the lung and the prostate. It is estimated that in 1998, 131,000 Americans will be diagnosed with the disease (95,000 colon, 36,000 rectum), and 56,000 will die. Rectal cancer is slightly more common in men; colon cancer is more common in women. The cumulative risk of an American to develop colorectal cancer during his or her life span is approximately 6 percent. The disease is related to age and occurs most often after age 50; screening efforts are directed to that age group. Five-year survival in North America is 40–50 percent.

COLON CANCER

Clinical Manifestations The presence of symptoms and their severity depend on the location and extent of the tumor. Tumors in the right colon present with occult bleeding, undetected by the patient, and may manifest with symptoms of iron-deficiency anemia. Such a finding in an adult male or postmenopausal female is an indication for colonoscopy. Tumors in the left colon may present with visible bleeding, change in bowel habits, and crampy abdominal pain secondary to partial obstruction. Large bowel cancer also may present for the first time with metastatic disease to the liver, ascites, and pulmonary metastases.

Acute Presentation A significant number of patients with large bowel malignancy will present acutely with perforation or obstruction. Untreated obstruction may lead to ischemia and perforation. Perforation also may occur primarily at the site of the tumor as a result of transmural growth and necrosis.

Diagnosis and Evaluation In patients with symptoms suggestive of colon cancer, endoscopy is the test of choice because of its sensitivity and ability to obtain tissue samples for histologic examination. Synchronous lesions exist in up to 5 percent of patients and should be ruled out before making a surgical plan of treatment. When endoscopy is not feasible, contrast studies of the colon are used. CT scan of the abdomen may be used to rule out liver metastases. Carcinoembryonic antigen (CEA) determination is done preoperatively as a baseline study. Its elevation suggests metastatic disease.

Surgical Treatment Large bowel surgery is classified as “clean contaminated.” When the bowel is open during operation, there is always some contamination of the operative field with colonic contents, including bacteria. Mechanical cleansing of the bowel before surgery significantly decreases the bacterial count and the risk of postoperative infection. Commonly used regimens include polyethylene glycol (PEG) lavage of the bowel and sodium phosphate laxatives. Additional reduction of bacterial counts in the bowel lumen is accomplished by oral antibiotics the day before surgery. The standard regimens are neomycin with erythromycin or neomycin with metronidazole. It also is a standard practice to administer intravenously broad-spectrum antibiotics just before surgery. Routine use of antibiotics postoperatively is not justified.

Operative Technique The objective of surgical treatment is to remove the involved segment of the bowel with the corresponding mesentery and the lymphatic channels. Because the lymphatics follow the arterial supply, the extent of resection corresponds to the arterial distribution. Any operation begins with thorough abdominal exploration to rule out peritoneal or hepatic metastases, as well as additional abdominal pathology (such as cholelithiasis). The segment of the colon is removed with the corresponding mesentery. The anastomosis can be performed manually or by stapling devices. It should be tension-free and with a good blood supply to the anastomosed edges. The common resections for colon cancer are right colectomy, extended right colectomy, transverse colectomy, left colectomy, and sigmoid colectomy. The resected specimen is inspected to assess surgical margins. A minimal margin of 5 cm on either side of the tumor is desirable (smaller margins are acceptable in surgery for rectal cancer).

Emergency Operation This is performed for obstruction, perforation, and rarely, bleeding. Diagnosis is confirmed by contrast studies, preferably with water-soluble contrast material and not barium. Because, by definition, the bowel is not prepared, there is a higher risk of anastomotic leak and infection. Resection of the involved segment is always desirable. The standard approach is to avoid primary anastomosis and perform a resection and a colostomy. However, in selected good-risk patients there is a place for intraoperative cleansing of the colon by lavage with primary anastomosis, avoiding colostomy and its associated morbidity, psychological distress, and the need to perform an additional operation for closure.

Staging and Prognosis Prognosis is related to the staging of the tumor. The Dukes staging system was favored because of its simplicity. The following is the Astler-Coller modification:

Dukes A: Tumor confined to the submucosa

Dukes B1: Tumor extending to the muscularis propria

Dukes B2: Tumor extending beyond the serosa of the bowel

Dukes C1: Lymph nodes are positive, with tumor not extending beyond bowel wall

Dukes C2: Lymph nodes are positive, with tumor extending beyond the bowel wall

Dukes D: Distant metastases

The uncorrected 5-year survival for Dukes A, B, and C is 85, 65, and 46 percent, respectively; the corresponding corrected values are 100, 78, and 54 percent. Other prognostic factors not incorporated in the Dukes system are the histologic differentiation of the tumor, presence of venous and perineural invasion, bowel perforation, elevated CEA level, and aneuploid nuclei.

Adjuvant Chemotherapy This is indicated for patients with Dukes C staging. The standard combination is 5-fluorouracil (5-FU) with levamisole or 5-FU with leucovorin. These regimens reduce mortality from the cancer by approximately 30 percent. Their value when residual metastatic disease is present is limited, and the side effects may outweigh the benefits.

Long Term Follow-Up Patients are followed with periodic liver function tests, CEA measurements, and CT scans of the abdomen if the previous tests are abnormal. Seventy percent of recurrent cancers will manifest within 2 years and 90 percent within 4 years. There is an increased risk of metachronous lesions (i.e., a second primary large bowel neoplasm that presents later), and follow-up with colonoscopy is indicated 1 year after the original operation and then every 3–5 years. Early detection of hepatic metastases may be of value in patients with only a few lesions and no extrahepatic disease. They can be treated with hepatic resection with up to 30 percent 5-year survival.

RECTAL CANCER

Similar to colon cancer, this usually is adenocarcinoma and derived from adenomatous polyps after the polyp-cancer sequence. The surgical approach is influenced by the proximity of the anal sphincter, the desirability of preserving the sphincter, and the proximity of the pelvic sidewalls limiting the extent of the resection. Unlike the rest of the large bowel, the rectum can be accessed easily through the anus for diagnostic and therapeutic purposes. Consideration in treatment planning includes the stage of the primary tumor, its relationship to the sphincter, and the presence of lymphatic or distant metastases.

Diagnosis Evaluation of rectal cancer includes digital examination to determine its size and degree of fixation, rigid sigmoidoscopy to assess its morphology and distance from the dentate line, and transanal ultrasound as the most accurate tool to assess depth of invasion and lymph node status. Pelvic examination should be performed in females to rule out invasion of the posterior wall of the vagina. The urinary system is assessed for possible ureteral obstruction or invasion of the prostate in males. CT scan is performed to assess the presence of liver metastases, which is an argument against radical treatment.

Surgical Treatment of Rectal Cancer When resection is performed, adequate distal and lateral margins should be accomplished, including the lymphatic-bearing area or the mesentery. If this allows preservation of the anal sphincter, continuity is reestablished by anastomosis. This procedure is low anterior resection, during which the peritoneal reflection is opened to dissect the extraperitoneal rectum. The procedure is technically demanding and can be aided by the use of end-to-end stapling devices. The lymphatic drainage of the rectum is in a cephalad direction. Accordingly, requirements for a distal margin in rectal cancer are less than those for colon cancer, and a 2-cm margin is considered sufficient.

In lower rectal lesions, when safe margins cannot be accomplished without impairing the anal sphincter, the resection involves the anus and the sphincter mechanism, with construction of an end colostomy. This operation is abdominal-perineal resection (APR).

In small, favorable distal rectal lesions, good cure rates can be accomplished by nonresective procedures such as transanal excision or transanal fulguration of the lesion. These may be supplemented with external-beam radiation. Another technique is that of endocavity radiation, applying a high dose of low-energy radiation directly to the lesion through a specially designed proctoscope.

Adjuvant Therapy for Rectal Cancer The overall 5-year survival rate for rectal cancer is less than 50 percent. Local recurrence rate in the pelvis is 20–30 percent and is associated with major morbidity and subsequent mortality. Local recurrence is high in rectal cancer because of the limited ability to perform wide resection within the confines of the pelvis. Multiple studies have assessed the role of adjuvant therapy in decreasing local recurrence and improving survival. The current trend is to administer chemoradiation preoperatively or postoperatively, with the chemotherapy component including 5-FU, which presumably acts as a radiosensitizer.

COMPLICATIONS OF SURGERY FOR COLON AND RECTAL CANCER

Complications can include bleeding, infection, cardiopulmonary complications such as myocardial infarction and pulmonary embolus (most of these patients should be on prophylactic low-dose heparin perioperatively), and wound complications. A specific problem related to rectal surgery is impairment of the urogenital innervation, sympathetic and parasympathetic, resulting in sexual dysfunction (impaired erection, retrograde ejaculation) or impaired bladder function.

A major complication in patients undergoing bowel resection is that of anastomotic leak. This is most common after low anterior resection when the anastomosis is extraperitoneal. Small leaks without sepsis can be managed conservatively. Larger ones resulting in sepsis may require proximal diverting colostomy or ileostomy and pelvic drainage. If, during the original operation, a low anterior anastomosis is considered to have a high risk for leak, it can be protected by proximal diverting colostomy or ileostomy.

Other Colorectal Tumors

Lymphoma The incidence of large bowel lymphoma has increased as a result of the AIDS epidemic, with the GI tract being a common site for the non-Hodgkin's HIV-associated lymphomas. Treatment includes resection with chemotherapy and radiation.

Large Bowel Carcinoid These are neuroendocrine tumors, with 2 percent of GI carcinoids occurring in the colon and 15 percent in the rectum. The tumor is located in the submucosa, usually is asymptomatic, and rarely behaves in a malignant fashion when it is less than 1 cm in size. Lesions bigger than 2 cm can invade the muscularis propria and metastasize to lymph nodes. Surgical treatment is local excision for smaller lesions and bowel resection for larger ones.

Anal Neoplasms

TUMOR OF THE ANAL MARGINS

This involves tumors below the dentate line. It includes squamous cell carcinoma, basal cell carcinoma, Bowen's disease (intraepidermal squamous cell carcinoma), and extramammary Paget's disease (tumor arising in the intraepidermal portion of the apocrine sweat glands). Diagnosis is made by biopsy, and the treatment is local excision with free margins. Advanced cases may require abdominal-perineal resection.

ANAL CANAL CANCER

This involves the transitional zone of the anal canal, 6–12 mm above the dentate line. Tumors in the area are referred to as squamous, basaloid, cloacogenic, or transitional. Diagnosis is established by biopsy. Small early lesions can be treated by local excision. For more advanced lesions, treatment formerly was abdominal-perineal resection. Currently, the Nigro protocol of chemoradiation, which combines chemotherapy with 5-FU and mitomycin C with external-beam radiation, is being used. It accomplishes a cure rate comparable with that of abdominal-perineal resection and has replaced radical surgery as the treatment of choice. If the regimen fails and the tumor recurs locally, abdominal-perineal resection is performed.

MISCELLANEOUS LESIONS

Colonic Pseudo-Obstruction (Ogilvie's Syndrome)

The syndrome is an ileus involving the proximal large bowel, usually to the level of the splenic flexure. The clinical presentation simulates mechanical obstruction. It usually is seen in acutely ill patients or after a major trauma. Water-soluble contrast study or colonoscopy should rule out mechanical obstruction. Colonoscopy also can be used to decompress the distended proximal colon and is successful in most patients. In patients in whom colonic distention progresses and the cecal diameter exceeds 12 cm with no response to conservative treatment, there is a risk of cecal perforation. Surgical decompression with cecostomy or colostomy is indicated.

Volvulus

Volvulus is a twisting of a segment of the colon over the mesenteric axis causing closed-loop obstruction that can lead to strangulation and gangrene. It accounts for less than 10 percent of large bowel obstruction in the United States.

SIGMOID VOLVULUS

This accounts for more than 90 percent of colonic volvulus, usually in chronically ill and elderly patients. The clinical presentation is that of abdominal pain, distention, and obstipation. Diagnosis is established by plain film revealing a distended sigmoid loop; it is verified by water-soluble contrast study. This shows a “bird's beak” deformity at the point of obstruction. Barium should not be used in these acutely ill patients. In patients with overt peritoneal signs, an operation is indicated. Otherwise, sigmoidoscopic or colonoscopic decompression is indicated and is successful in most patients. The recurrence rate is high, and elective surgical resection is indicated in patients who are reduced without surgery.

CECAL VOLVULUS

This occurs in younger patients and is related to an anatomically redundant cecum and right colon. The patient presents with abdominal pain, nausea, and vomiting. Plain abdominal x-rays reveal a distended cecum. The diagnosis may be verified with a water-soluble contrast study. Colonoscopy is used to reduce the volvulus nonoperatively. When this fails or in cases of overt peritoneal signs suggesting gangrene of the cecum, surgery is indicated. Surgical treatment may be detorsion, cecopexy, tube cecostomy, or right colectomy.

TRANSVERSE COLON VOLVULUS

This is the least common type of colonic volvulus. Presentation, diagnosis, and treatment are similar to those of sigmoid colon volvulus.

Ischemic Colitis

This usually is a disease of the elderly. It occasionally is related to occlusion of a major mesenteric vessel (such as ligation of the inferior mesenteric artery during surgery for abdominal aortic aneurysm), but in the majority of patients no specific vascular disease or underlying cause is identified. It is presumed to be secondary to low flow without arterial occlusion. Angiogram has no diagnostic role. Clinical presentation depends on the severity of the ischemia. Most cases are mild and present with low abdominal pain, passage of bright red blood per rectum, and mild to moderate abdominal tenderness. The involved colonic segment usually is around the splenic flexure, which is the watershed area between the superior and inferior mesenteric arterial supply. Diagnosis is established by contrast studies that show “thumbprinting” of the involved colonic segment and colonoscopy that shows edema and ecchymosis of the mucosa. Mild and moderate cases respond to medical treatment, including intravenous fluids and antibiotic. Severe cases with full-thickness necrosis of the bowel wall require surgery and resection. Follow-up studies (barium enema or colonoscopy) are indicated a few weeks after the acute event to rule out postischemic strictures.

Radiation Proctitis

This usually is associated with radiation for cervical and uterine cancer, bladder cancer, or prostate cancer. The rectum, because of its proximity to the cervix and prostate, is the part of the large bowel most commonly affected by radiation. Injury usually occurs when radiation exceeds 5000 cGy. In early stages, it manifests with mucosal edema and acute ulceration. The patient presents with abdominal pain, diarrhea, nausea and vomiting, tenesmus, and rectal bleeding. In the chronic stages, there is progressive vasculitis with fibrosis and thickening of the bowel wall and possible stricture formation, perforation, or fistulization. The main symptoms in the chronic stage are tenesmus and bleeding. Treatment includes stool softeners, topical 5-aminosalicylic acid preparations, and steroid enemas. Local application of 10% formalin solution to the rectal mucosa is effective in controlling persistent bleeding. In patients whose symptoms are not controlled by conservative measures, colostomy or proctectomy may be necessary.

Rectal Prolapse

This involves eversion and protrusion of the full thickness of the rectum through the anus. It is related to defective fixation of the rectum to the pelvic sidewalls. It is more common in women, in the elderly, and in institutionalized patients. Symptoms include sensation of a mass, anorectal pain, bleeding, mucous discharge, and incontinence. In the early stages the prolapse reduces spontaneously. As the condition progresses, manual replacement may be required. In extreme cases, the rectum may be irreducible with subsequent risk of necrosis, which may require an urgent operation. Surgical treatment options include transabdominal resection, fixation of the rectum to the sacrum, or resection of the prolapse by perineal approach. The latter, by avoiding laparotomy, can be done with relative safety on high-risk patients. Anal encircling procedures usually have poor results and are not recommended.

Anal Fissure

This is a painful lineal ulcer in the anal canal below the dentate line, located in the posterior midline in 90 percent of the patients. The typical symptoms are severe “cutting” type pain on defecation and a small amount of blood on the toilet paper or stool. The pain may last for a few hours after bowel movement. The cause is passage of hard stool through an anal sphincter that does not fully relax, causing a tear in the anoderm. When a fissure becomes chronic, a skin tag develops caudad to it (“sentinel pile”), and the anal papilla cephalad to it becomes hypertrophic. Diagnosis is by direct inspection, preferably in a jackknife position. Severe pain and tenderness may preclude any additional examination beyond inspection on the initial presentation. A large proportion of patients respond to dietary fiber (preferably psyllium derivatives) and stool softener (sodium docusate).

Two newly described treatments are aimed at relaxing the internal sphincter. Application of 0.3% topical nitroglycerine cream to the anal canal was reported to induce healing in 60 percent of patients. Intrasphincteric injection of botulinum toxin (Botox) transiently paralyzes the sphincter for 6 months, allowing healing of the fissure. Surgery is indicated in patients who fail conservative treatment and have significant symptoms. It should be used only as a last resort because of the associated risk of anal incontinence, especially in females. The operation is lateral internal sphincterotomy, dividing the distal part of the hypertrophic internal sphincter caudad to the dentate line. It usually is done under local anesthesia on an outpatient basis. The success rate is 90–95 percent.

Rectovaginal Fistula

The most common cause is obstetric injury, including midline episiotomies that do not heal well. Other causes include Crohn's disease, malignancies, and radiation injuries. The patient describes the distressing symptom of passing gas and stool through the vagina. Diagnosis usually is evident on sigmoidoscopy and vaginal examination. Treatment depends on the cause of the fistula, its size, and its level (high or low). Most patients with obstetric injury can be treated with endorectal mucosal advancement flap, which obliterates the fistula on its rectal aspect. In patients with malignancy or severe Crohn's disease, proctectomy and colostomy may be required.

Pruritus Ani

Perianal itching often is idiopathic but may be related to diet, specifically ingestion of coffee, dairy products, alcohol, and diet drinks. Pinworm infestation is the most common cause in children. Treatment includes dietary modification and short-term use of local steroid preparations.

Hemorrhoids

Hemorrhoidal tissue is a part of the normal anal anatomy, composed of a cushion of submucosal vascular and connective tissue, and is located in the upper part of the anal canal, above the dentate line. The tissue is more prominent in the right anterior, right posterior, and left lateral positions, thus forming three separate complexes. The presumed function of this tissue is to improve closure of the anal canal. The term external hemorrhoids refers to the vascular complexes underneath the anoderm, below the dentate line. Hard stool and prolonged straining on defecation may cause engorgement and dilation of the veins and stretching of the connective tissue, resulting in bleeding and prolapse of tissue, the two main symptoms of hemorrhoids. While hemorrhoids are the most common cause of rectal bleeding, other causes, especially neoplasms, have to be ruled out. This is particularly important in older patients. Uncomplicated internal hemorrhoids usually do not cause pain. In patients who complain of significant anal pain, other causes have to be looked for (e.g., abscess, fissure, thrombosed external hemorrhoids).

Internal hemorrhoids are arbitrarily classified to four degrees of severity:

Bleeding only
Bleeding and prolapse of tissue outside the anus on defecation that reduces spontaneously
Prolapse that requires manual reduction
Irreducible prolapse

Treatment Most patients respond to dietary fiber (psyllium derivatives that are hydrophylic are preferable over “dry” fiber). For patients who continue to bleed, nonsurgical treatments, including rubber band ligation, photocoagulation with infrared light, and injection of sclerosants, are used. Cryosurgery, which was popular in the past, is not recommended because of its side effects. Excisional hemorrhoidectomy is not a minor operation, has a significant complication rate, and should be used only as a last resort.

External hemorrhoids occasionally present with thrombosis, manifested as a painful lump under the anoderm. This usually can be excised with local anesthesia as an office procedure. Incision and evacuation of the clot are not recommended because of the high rate of recurrence and bleeding.

For a more detailed discussion, see Kodner IJ, Fry RD, Fleshman JW, Birnbaum EH, and Read TE: Colon, Rectum, and Anus, chap. 26 in Principles of Surgery, 7th ed.