Bleeding Per Anus

The occurrence and clinical significance of overt blood loss per rectum varies according to the clinical situation. Using a Medline literature search, the incidence of rectal bleeding in the general population was estimated to be approximately 20 per 100 people per year; in general practice patients, it was approximately 6 per 1,000, and in referral medical specialists, it was about 0.07 per 1,000 per year. ¹ The predictive value of anorectal blood loss for colorectal malignancy was estimated to be less than 1 in 1,000 in the general population, approximately 0.2 per 1,000 in general practice, and as many as 360 per 1,000 in referral patients.

The character of the bleeding often suggests the diagnosis. Blood that drips into the toilet bowl and is bright red, free, and separate from the stool is frequently associated with bleeding internal hemorrhoids. Blood that is on the toilet tissue tends to be associated with anal fissures or an abrasion of the anal canal. Melena can be caused by any pathologic process in the right colon or higher up in the gastrointestinal (GI) tract. The association of blood and mucus usually indicates a low-lying carcinoma or, more frequently, an inflammatory condition, such as ulcerative colitis or Crohn’s disease. If blood clots are being passed, the source is usually of colonic origin.

Pain

The lower anal canal obtains its innervation from the somatic nervous system and any pain-producing lesion in the anal canal is likely to be described as sharp, burning, or stinging. Sharp anorectal pain that occurs during and following a bowel movement is usually associated with an anal fissure or an abrasion in the anal canal. Tenesmus, a symptom complex of straining and the urge to defecate, is frequently associated with inflammatory or neoplastic conditions of the anorectum. The pain associated with a perianal abscess usually is described as constant and throbbing in nature. Pain that increases in intensity when the patient coughs or sneezes is often associated with an intersphincteric abscess.

Anorectal pain may be referred to the sacral region but is usually related to bowel movements. Pain associated with levator ani muscle spasm or proctalgia fugax (rectal muscle spasm) will vary from a pressure feeling to a stabbing pelvic pain that is of short duration and is not related to activity or bowel movements. Rectal pain may also be referred from aneurysmal dilatations in the pelvic vascular tree or from retrorectal tumors and usually presents as a feeling of fullness. Coccygeal pain usually results from trauma to the ligaments or periosteum of the coccyx or an inflamed presacral cyst.

Abdominal pain tends to be nonspecific. Pain from the cecum usually is located in the right lower quadrant, while pain from the sigmoid colon is located in the left lower quadrant. Pain experienced in the lower rectum may be referred pain from the sigmoid colon, whereas pain originating in the rectum itself usually is experienced in the perineum and rarely in the hypogastrium. Obstruction of the left colon may manifest as pain in the right lower quadrant because of the distention of the cecum. The character and duration of pain and its relation to meals should be determined.

Abdominal pain that originates from the colon may be crampy in nature when related to an intramural lesion or to excessive colonic contraction or distention, or it may be associated with peritoneal irritation when related to any inflammation in the colon. When the mesentery of the colon is stretched, pain will be experienced, and this can be duplicated in the process of performing a proctosigmoidoscopic or colonoscopic examination. Peritoneal pain may be secondary to colonic disease when there are adhesions between the colon and the parietes. Sites of referred pain to the body surface are determined by the same principles as referred pain elsewhere; pain from the colon is referred to just above the symphysis pubis, and rectal pain can go directly to the sacral area.

Abdominal pain may be a manifestation of anorectal disease when the supralevator space is involved. Because this space has peritoneum as its “roof,” a suppurative process may result in signs of peritoneal irritation.

Change in Bowel Habits

Normal bowel movement frequency varies from three per day to three per week. ^{2 , 3} To a patient, constipation may mean a variety of conditions, such as stools that are infrequent, hard, small, or difficult to pass. To determine the necessity for further investigation, it is important to know the duration of the constipation, whether the onset is recent, or if the condition is a chronic one. Constipation can also result from a pelvic floor disorder.

Diarrhea is a symptom of many GI diseases. The duration, amount, character, and frequency of the diarrhea should be determined. Clear watery diarrhea may be from a large secretory rectal villous adenoma. A bloody mucous diarrhea may indicate inflammatory bowel disease. Operative procedures such as vagotomy, cholecystectomy, or gastric or small bowel resection may alter GI motility, absorption, and secretion, and consequently will alter bowel habits. Patients who have had a jejunoileal bypass for morbid obesity are subject to many anorectal problems associated with diarrhea.

Discharge

Mucus is secreted by the goblet cells of the colonic and rectal mucosa and may be seen in the stool under many different circumstances. It may be the result of normal production of mucus, ¹ the early sign of a villous adenoma of the rectum, ² the indication of an early colitic condition, ³ or caused by chemical irritants. ⁴ The packaged buffered phosphate enemas (e.g., Phospho-Soda) can elicit a tremendous response from the bowel and extra mucus may be seen on endoscopic examination of the bowel after administration of such an enema. Mucus associated with bleeding may be a sign of a neoplasm or an inflammatory process.

Mucus should normally not leak through the anus unless the patient is incontinent. Soiling of underwear may be a sign of rectal mucosal prolapse, ectropion from a previous hemorrhoidectomy, or overproduction of mucus, such as occurs with a villous adenoma.

Purulent discharge is indicative of an infectious process. A history of purulent discharge and pain is characteristic for an anorectal abscess, whereas a painless purulent discharge more likely is due to a fistula-in-ano. Passing pus per rectum may indicate a gonococcal proctitis or a spontaneously drained intersphincteric abscess.

Fecal soiling of underwear is usually asymptomatic. However, it may be a consequence of early postoperative anorectal procedures, such as hemorrhoidectomy, internal sphincterotomy, and fistulotomy. Fecal soiling is relatively common in the elderly. Fecal soiling must not be mistaken as fecal incontinence.

Perianal Swelling

One must always determine whether or not a perianal swelling is painful and whether it has discharged blood or pus. The swelling also might be intermittent as would be expected with a prolapsing hypertrophied anal papilla. If the swelling is associated with fever and chills, an anorectal abscess should be suspected. The common swelling at the anal verge usually is a thrombosed external hemorrhoid, which develops rather quickly and, if ulcerated, is associated with pain and occasional bleeding.

Pruritus

Pruritus ani (intense itching) is a common symptom associated with anorectal pathology. Most often, it occurs in patients who have loose stools and are unable to properly cleanse the anal area. Pruritus also may be associated with the healing phase of an anal condition. Severe pruritus ani is usually associated with a mucoid discharge, which may be blood tinged from the open ulceration of the perianal skin. The patient always should be questioned regarding the use of antibiotics, because these drugs may be the cause of the pruritus ani. In rare cases, pruritus ani in adults may be caused by Enterobius vermicularis (pinworms). Most of these adults have a history of contact with infected children.

Prolapse

In questioning the patient who presents with a protrusion from the anal aperture, it should be determined whether the prolapse occurs only at the time of defecation or whether it occurs independently. Independent prolapsing is more suggestive of a hypertrophied anal papilla or a complete rectal procidentia. Does the prolapse reduce itself spontaneously, or must it be replaced manually? This may suggest the magnitude of the problem. Frequently, the patient can give an idea of the relative size of the prolapsing mass; this information often helps in making the diagnosis. The most common prolapsing condition is rectal mucosal prolapse associated with prolapsing hemorrhoids. This must be differentiated from true procidentia of the rectum. Large hypertrophied anal papillae also are known to prolapse from the anal canal. Polyps in the rectum can prolapse; however, this usually is seen in a child with juvenile polyposis or in an elderly patient with a massive villous adenoma.

Incontinence

When a patient presents with a history of incontinence following a previous anorectal surgical procedure, the details of that procedure must be elicited to evaluate the complaints completely. In a parous woman, a good obstetric history should be obtained regarding the nature of an episiotomy and any complications associated with it, as well as the nature and type of delivery. In bedridden elderly patients, fecal impaction may be the cause of overflow incontinence.

Loss of Weight

It is important to note the amount of weight loss occurring over a given time period. Rapid loss of weight without obvious reasons (such as dieting) may indicate GI disease or malignancy.

Flatulence

All patients pass gas through the rectum, so it must be determined whether there is actually an excessive passage of flatus or merely an unusual sense of awareness of the normal passage. Gas in the GI tract is either “swallowed” or the result of bacterial action on luminal contents. Most patients with increased flatulence are found to have a dietary indiscretion in the form of excessive intake of gas-producing substances, rather than a specific malady of the GI tract. Patients are not aware that fermentation is taking place all the time in the bowel. A simple test is to have the patient intake only a clear liquid diet for 24 hours and observe the amounts of flatus following this therapeutic test. Frequently, the patient will learn that very little gas is formed when there is not an excessive amount of food in the GI tract. Another simple test is to ask the patient if flatus was experienced on the day of a barium enema study. Often, the patient will indicate that there was freedom from flatus for the first time when the GI tract was cleaned out for the X-ray study.

Studies by Levitt ⁴ have shown that hydrogen and methane are produced solely by bacteria and are not a product of human cellular metabolism. Levitt also has shown that hydrogen production is negligible in the fasting state; it appears that colonic bacteria are dependent on ingested fermentable substrates (carbohydrates) for hydrogen production. Certain vegetables, particularly legumes, contain a high concentration of indigestible oligosaccharides, which are nonabsorbable even by normal subjects, and these oligosaccharides account for the notorious gaseous properties of legumes. Carbon dioxide can be produced by bacterial fermentation or by the reaction of bicarbonate and acid. Digestion of an average meal could theoretically produce several hundred milliequivalents of acid, thus yielding 4,000 mL of carbon dioxide. Although excessive gas is assumed to be a common cause of “functional abdominal complaints,” there are little hard data to support this assumption. Passing gas through the vagina or through the urethra usually is indicative of a fistula to the GI tract. Occasionally, gas-forming organisms in the bladder may give rise to pneumaturia without a fistula, but this is rare except in the diabetic patient. Instrumentation of the bladder by a Foley or cystoscopy may explain transient air. A complete GI evaluation is mandatory if a history of pneumaturia or flatus per vagina is obtained.

Anorexia

Anorexia is a lack or loss of appetite for food. Frequently, this appetite change is psychogenic in origin, as with depression, worry, and boredom, or it may be caused by drugs such as digitalis preparations, sulfasalazine, and antihypertensive agents. Anorexia is a common symptom for patients with an acute viral hepatitis and/or carcinoma. Numerous signals have been implicated in the short-term control of appetite. These include changes in blood glucose, free fatty acid, and amino acid concentrations; altered neuronal activity resulting from distention of the GI tract; or alterations in the concentrations of various hormones such as insulin, glucagon, bombesin, and cholecystokinin. ⁵ Other clinical factors that may contribute to the development of anorexia and reduced food intake in patients with carcinoma include intestinal obstruction, radiation therapy, chemotherapy-induced nausea and vomiting, altered taste sensitivity, and oral ulceration.

Proctosigmoidoscope

Three sizes of proctosigmoidoscopes are available (▶ Fig. 3.3). A19-mm 25-cm scope is the standard size and should be used for polypectomy or electrocoagulation. A 15-mm 25-cm scope is an ideal size for general examination. It is much better tolerated by the patient, causing less spasm of the rectum and thus minimal air insufflation, yet enables as adequate an examination as the standard-size scope. An 11-mm 25-cm scope should be available for examining the patient who has an anorectal stricture, such as in Crohn’s disease. More recently, a disposable standard-size proctosigmoidoscope has become popular for routine examination.

Flexible Sigmoidoscope

The standard flexible fiberoptic sigmoidoscope (FFS) is 60 cm long (▶ Fig. 3.4). It has all the features of a colonoscope. Because of the shorter length of the flexible sigmoidoscope, its cost, maintenance, and durability are considerably better than those of the colonoscope.

Colonoscope

Colonoscopy was introduced to clinical practice in 1970 and has become an established component of colon and rectal surgery. Indications, equipment, and the procedure are discussed in Chapter 4.

Ancillary Equipment

A ball-tip electrode with an insulated shaft works well for coagulating a small rectal or sigmoid polyp (▶ Fig. 3.5a). A suction–coagulation electrode is ideal for coagulating a bleeding area, such as after biopsy of rectal mucosa or a lesion (▶ Fig. 3.5b). It is more versatile because the oozing of blood can be sucked dry during the coagulation, and the gas and smoke that are produced can be readily eliminated. A piece of wire or a needle always should be available to push the plug of tissue or blood out of the insulated shaft.

There are two types of electrocautery snare wires available commercially (▶ Fig. 3.6). A rigid-wire snare, known as the Frankfeldt snare, has been in use for a long time and is good for snaring small- or medium-size polyps. A soft-wire snare has a larger loop and is easier to use, especially for larger polyps or for piecemeal snaring; however, the problem with this type of wire is that it is too soft and bends easily. Several snare wires should be available as spare parts. ¹⁰

There are basically two types of biopsy forceps for use with the proctosigmoidoscope—the cup-shaped forceps and the Turrell biopsy forceps. Both types are excellent for biopsy of lesions or rectal mucosa. The size of the specimen obtained is between 5 and 8 mm. Because of the relatively large size, electrocoagulation usually is required to stop the bleeding. Alligator-type forceps for retrieval of polyps or foreign bodies should be available (▶ Fig. 3.7).

Because anorectal probes for fistula-in-ano or sinus tracts cause considerable pain, they should only be used in the operating room when the patient is under anesthesia. The grooved Lockhart-Mummery fistula probes are suitable for diagnosis and fistula surgery (▶ Fig. 3.8).

Rubber Band Ligation Equipment

Rubber band ligation equipment, including ligator, O ring, and forceps, should be available for immediate use (▶ Fig. 3.9). Several forceps have been advocated for this technique; however, an Allis forceps may suffice. A suction hemorrhoid ligator is also available. It has the advantage that one can apply the ligation without needing an assistant (▶ Fig. 3.10). Another advantage is that only the redundant mucosa is sucked into the cup for ligation.

Sclerosing Equipment

Sclerosing procedures require a syringe loaded with a solution of either 5% phenol and vegetable oil or 5% quinine and urea hydrochloride. However, sclerosing of hemorrhoids has been replaced largely by rubber band ligation.

Miscellaneous Items

Along with the necessary equipment already described, there are accessories essential for the examination. A good suction system (either water or motor suction) is indispensable. A long metal or plastic suction rod must be available. Lubricant jelly is required in every case. A 2% lidocaine (Xylocaine) jelly also should be available, especially for patients with anal fissures or abrasions. Rubber or plastic gloves are essential. (Some people are allergic to rubber gloves.) A 1.5- to 2-inch 27-gauge needle, a 3-mL syringe, and a local anesthetic should be available. Scalpels, scissors, needle holders, tissue forceps, and suture materials also should be on hand. An irrigating syringe or bottle for irrigating via the proctosigmoidoscope also is needed. A pulsating water injection device (i.e., Waterpik ¹ ) can be easily adapted for irrigating via the colonoscope or flexible sigmoidoscope and should be available. An area with proper antiseptic solution must be arranged for cleaning the instruments after they are used. Disposable buffered phosphate enemas should be available for use when the rectum is loaded with stool. Ideally, a toilet should be in or near the examining room. Soft paper tissues are needed to wipe the lubricant jelly from the anal area after the examination. Basic resuscitation equipment should be available, especially when minor surgical procedures are being performed.

Abdomen

Inspection of the abdomen may reveal asymmetry suggestive of a neoplastic mass or enlargement of the internal organs. Distended abdominal veins suggest portal hypertension or obstruction of the inferior vena cava. Pulsation from an abdominal aortic aneurysm may be seen in very thin patients. Palpation should be aimed at detecting any tenderness, peritoneal irritation, or abdominal mass. The scar from a previous large bowel resection should be examined for healing, sinus or fistula, and metastatic mass.

Perineum

The most common site of recurrence of rectal carcinoma is the pelvis and perineum. Follow-up examination should encompass the perineal wound to determine if it has healed completely or has any evidence of sinus, mass, or tenderness.

Groin

Anorectal carcinoma that has invaded into or below the dentate line may metastasize to the inguinal lymph nodes. Therefore, the presence or absence of enlarged inguinal nodes should be recorded. Enlargement of these nodes before or after excision of an anorectal lesion requires further management or a change in management approach.

Positioning

Although the inverted prone jackknife position on a proctoscopic table is most popular and is extensively used in the United States (▶ Fig. 3.11a), the left lateral (Sim’s) position with the buttocks projecting slightly beyond the edge of the examining table is as good for examination and is much more acceptable to the patient (▶ Fig. 3.11b). The prone jackknife position should not be used in conditions such as acute glaucoma, retinal detachment, severe cardiac arrhythmia, severe debilitation, late pregnancy, and recent abdominal surgery.

Inspection

Inspection of the anal area always should precede any other examination, and for this, good lighting is essential. The shape of the buttocks should be noted, because this information can be useful in determining the position in which to place the patient for the operation and the type of anesthetic to use. ¹¹ The cheeks of the buttocks are gently spread to gain exposure. Skin tags, excoriation, and change in color or thickness of the anal verge and perianal skin can be detected quickly. A scarred, patulous, or irregularly shaped anus may give clues to the cause of anal incontinence. Particularly in multiparous women, the anal verge may be pushed down too far during straining—a feature of the perineal descent syndrome. ¹² Prolapse of the rectum (procidentia) is best demonstrated by asking the patient to strain while in a lateral position or sitting on the toilet. When the anal verge is pricked with a needle, the external sphincter visibly contracts because of anal reflex. It is useful for testing the sensibility of the anal canal, which may be absent in areas of a previous scar or defect, or in patients with an underlying neuropathy.

Digital Examination

To begin the digital examination, the index finger should be well lubricated with a lubricant jelly, and the finger pressed on the anal aperture to “warn” the patient. Then, the finger should be gradually inserted and swept all around the anal canal to detect any mass or induration. In men, the prostate should be felt. In women the posterior vaginal wall should be pushed anteriorly to detect any evidence of a rectocele. Anal tone, whether tight or loose, can be easily estimated. A stricture or narrowing from scarring or a defect in the internal or external sphincters from a previous operation can be felt. A fibrous cord or induration in the anal area and anal canal may indicate a fistulous track. The external sphincter, puborectalis, and levator ani muscles can also be appreciated by digital examination. When the puborectalis is pulled in the posterior quadrant, the anus will gape but will close immediately when the traction is released. ^{13 , 14} Persistence of the gaping indicates an abnormal reflex pathway in the thoracolumbar region, commonly seen in paraplegic patients. The finger should press gently on these muscles for signs of tenderness. When a person with good sphincter function is asked to contract the muscles, the examiner not only feels the squeeze of the muscle on the examining finger but also feels the finger pulled forward by the puborectalis muscle.

Anoscopy

Anoscopy, as the name implies, is the examination of the anal canal. The anoderm, dentate line, internal and external hemorrhoids, and lower part of the rectal mucosa can be seen through the anoscope. Anoscopy should not begin until a digital examination has been completed. For most cases, an enema is not required. Insertion of the anoscope always should be done with the obturator in place. The obturator is removed during examination and reinserted to rotate the instrument to another area. If an inverted jackknife position is used, the examination table should not be tipped down more than 10 to 15 degrees. If a left lateral position is used, an assistant needs to pull up the right cheek of the buttocks for exposure. During examination, the patient is asked to strain, with the anoscope sliding out to detect any prolapse of the rectal mucosa and the anal cushion. Excoriation, metaplastic changes, and friable mucosa indicate a prolapsed hemorrhoid.

Proctosigmoidoscopy

Although a standard proctosigmoidoscope is 25 cm in length, the average distance that the scope can be passed is 20 cm. In men, the scope can be passed to 21 to 25 cm half of the time, and in women it can be passed that distance one-third of the time. ¹⁵ Proctosigmoidoscopy is suitable only to examine the rectum and, in some persons, the distal sigmoid colon. The pain experienced from proctosigmoidoscopy is from stretching the mesentery of the rectosigmoid colon when the scope is pushed against the rectal wall and from the air insufflation. When properly performed, proctosigmoidoscopy should produce no pain at all or only mild discomfort. Most patients are fearful of the examination because of past bad experience with the procedure or from what they have heard. A few words of reassurance will be helpful. Since many patients feel undignified in the “bottom-up” positioning, a left lateral position can be used instead to alleviate this feeling.

Technique: With the obturator in place and held steady with the right thumb, the proctoscope is gently inserted into the anal canal, aiming toward the umbilicus for a distance of about 4 to 5 cm. Then the scope is angled toward the sacrum and advanced another 4 to 5 cm into the rectum. The obturator is removed, and the bowel lumen is negotiated under direct vision. Air insufflation is limited to the amount necessary to open the lumen. When an angle is encountered, the scope is withdrawn 3 to 4 cm and then readvanced. This may be repeated several times to straighten the angulation. If further advancement is unsuccessful, the procedure is terminated at this point. Careful examination is done as the instrument is withdrawn. It usually is necessary to insufflate a small amount of air for good visualization of the lumen. The instrument should be rotated on withdrawal to ensure examination of the entire circumference. The mucosal folds (valves of Houston) can be flattened with the tip of the scope to see the area behind them.

The length of insertion should be measured from the anal verge without stretching the bowel wall. Some physicians measure it in relation to the dentate line. This is more cumbersome because one also needs to measure the distance to the dentate line and subtract from it the distance to the anal verge. The appearance of the mucosa and depth of insertion should be accurately described. If a lesion is seen, the size, appearance, location, and level must be recorded. If a biopsy is performed, the location, level, number of biopsies, and whether electrocoagulation is necessary should be noted.

Ideally, a phosphate enema should be given within 2 hours of the examination. If the patient has had a bowel movement that morning, an enema usually is unnecessary. Mucus and watery stool can be easily aspirated. Even if there is some formed stool, the scope can be slipped between the fecal mass and the colonic wall. However, a large amount of solid or soft stool can impede further passage of the scope; in this situation, a phosphate enema should be given in the examining room, or the patient should return at some later date with better preparation.

Flexible Sigmoidoscopy

A flexible sigmoidoscope is no longer fiberoptic but contains a video chip at the tip of scope. This video chip transmits the image through the processing unit of the monitor. The entire sigmoid colon can be reached by the flexible sigmoidoscope in 45 to 85% of cases, and in a few, the splenic flexure also can be visualized. ^{16 , 17} The discrepancies in success depend on patient selection and the experience of the endoscopist. For selective screening examination, flexible sigmoidoscopy has a three to six times greater yield than does proctosigmoidoscopy in detecting colonic and rectal abnormalities, especially neoplasms. ^{18 , 19} Because of this higher yield, proponents of flexible sigmoidoscopy have discarded proctosigmoidoscopy. ²⁰ With the advance in technology of colonoscopy and because large bowel carcinomas have shifted proximally during the last few decades, the role of proctosigmoidoscopy is now limited to examination of the rectum and is no longer adequate for the screening of large bowel neoplasms.

The role of flexible sigmoidoscopy is difficult to define. Although this type of sigmoidoscopy detects more lesions than proctosigmoidoscopy, flexible sigmoidoscopy cannot be considered adequate when a complete colonic examination is indicated. However, it plays a superior role to proctosigmoidoscopy in case finding. Because barium enema studies miss some lesions in the rectosigmoid and sigmoid colon, a successful flexible sigmoidoscopy that is followed by an air-contrast barium enema gives a more accurate examination than an air-contrast study alone or an air-contrast barium enema combined with rigid proctosigmoidoscopy. ²¹ Although the flexible sigmoidoscope is easier to handle and learn to use than the fiberoptic colonoscope, proper training is nevertheless necessary. The basic principles of technique, the limitations, and the risk of complications must be fully understood.

Technique: Because flexible sigmoidoscopy is designed for examination of the left colon, a formal bowel preparation with laxatives is unnecessary. Normally, one or two phosphate enemas before the examination are adequate.

The examination is best performed with the patient in a left lateral position, although a prone position is sometimes preferred by some examiners. Sedation is unnecessary. The anal canal is lubricated by digital examination. A well-lubricated flexible sigmoidoscope then is inserted. Advancement of the scope is performed under direct vision. Pushing the scope through a bend in the bowel is a poor technique. Instead, the scope should be withdrawn to straighten the bowel. The key to success is short withdrawal and advancement of the scope or a to-and-fro movement, together with rotating the instrument clockwise and/or counterclockwise as needed. Use of air insufflation should be kept to a minimum. The procedure should be completed within 5 to 10 minutes. If a lesion is detected and proved by biopsy to be a neoplasm, a complete colonic investigation may be indicated ideally by total colonoscopy at some later date. A polyp up to 8 mm in size can be sampled with coagulation (hot) biopsy forceps or biopsy and electrocoagulation. A larger polyp should be reserved for colonoscopy and polypectomy. To prevent possible gas explosion due to hydrogen or methane gas in the lumen, air should be exchanged in the colon and rectum with repeated insufflation and suction.

Computed Tomography Angiography

Computed tomography angiography (CTA) uses a multidetector row CT with thin collimation, with intravenous contrast, multiple image postprocedure processing techniques to produce high-quality imaging. Factors influencing the ability to visualize active bleeding at CT are multiple and include the nature of the bleeding lesion (bleeding rate, intermittence), patient factors (hemodynamic status, body mass index), the CT technique (rate of injection, concentration of iodine in contrast material, number of phases, type of scanner, postprocessing), and the experience of the radiologist. ³³ The addition of imaging phases to the CTA study may provide more information but also increases the total radiation dose. Findings of recent studies suggest that the highest sensitivity for detecting intestinal bleeding is achieved by means of a dual-phase protocol (arterial and portal venous phases). ³⁴ The two-phase protocol improves depiction of extravasated contrast medium during the arterial phase alone and also provides information about the cause of the bleeding. ³⁵ The preliminary unenhanced scan minimizes misinterpretations of hyperattenuating material that can mimic contrast medium extravasation and can be a cause of false-positive results, such as retained contrast material in diverticula, medications, wall suture material, hemostatic clips, or calcifications. ³⁶

The inclusion of CTA in the diagnostic algorithm of acute lower intestinal bleeding helps identify patients with active bleeding and accurately determine the site of the bleeding. This information is helpful for directing therapy and, when necessary, for selecting the most appropriate hemostatic intervention: endoscopic, angiographic, or surgical. Precise anatomic localization of the bleeding point allows a targeted endovascular embolization, with a reduction in the number of angiographic series and a resulting savings in time, radiation dose, and the load of contrast material administered. ³⁷ Since even massive GI tract hemorrhage can be intermittent, the finding of active bleeding or a potential hemorrhagic lesion serves to direct the interventional radiologist to the area of concern and increases the success rate of endovascular therapeutic techniques. ^{38 , 39} Conversely, a completely negative CT angiogram decreases the likelihood of subsequent angiographic identification of bleeding and might warrant a more conservative treatment and an initial “wait-and-see” strategy, with the possibility of repeating the CT angiogram in cases of re-bleeding. ⁴⁰

The identification and anatomic localization of the lesion that is potentially responsible for the hemorrhage and its characterization as vascular, inflammatory, diverticular, or neoplastic (even in a patient who is not actively bleeding) are important for planning the definitive treatment. ⁴¹ The accuracy in detecting the bleeding lesion has ranged from 80 to 85%. ^{41 , 42 , 43}

A meta-analysis confirmed a good correlation between conventional angiography and CTA in the identification of the source of bleeding. ³³ In some circumstances, the sensitivity of CTA may even exceed that of conventional angiography. ⁴² One limitation of CTA is the necessity to use intravenous contrast media, which may damage kidney function, limiting its use in patients with renal insufficiency. The ready availability of CTA and its ability to localize the source of bleeding has encouraged many centers to use CTA as the initial test in significant GI bleeds in patients with normal renal function. ^{44 , 45}