Improved Outcomes in Colon and Rectal Surgery part 13 pdf

1 improved outcomes in colon and rectal surgery (CTA) has become the method of choice for imaging the pulmo- nary vasculature, and has replaced invasive pulmonary angiog- raphy as the reference standard for diagnosis.(112–117) Another advantage of CTA over pulmonary angiography is the ability to identify alternative or additional diagnosis such as: atelectasis, pneumonia, pulmonary edema, pleural, and pericardial effusions, and many others. CT venography (CTV) combined with CTA can be used as a comprehensive examination of the deep venous system to detect both PE and deep vein thrombosis (DVT). CTV is performed by scanning of the pelvis from the iliac crest to the popliteal fossa approximately 120 s after completion of the CTA. CTV could potentially salvage the occasional suboptimal PE study by diagnosing a DVT and guide interventions such as vena cava filter placement. Numerous studies have cited 97% agreement between CTV and US.(118–122) The addition of CTV increases the gonadal radiation exposure, and should be used selectively on the basis of risk-benefit considerations (e.g., avoided in young patients and reproductive female patients).(116) Appendix Acute Appendicitis MDCT has a high sensitivity (91–100%) and specificity (91– 99%) in diagnosing acute appendicitis (123–126). The diagnosis of acute appendicitis is based on finding: an abnormally dilated (>6 mm), enhancing appendix; appendix surrounded by inflam- matory periappendiceal fat stranding; focal thickening of the base of the cecum; periappendiceal abscess; or obstructing calci- fied appendicolith (Figures 11.30A and 11.30B). The most com- mon reason for a false-negative diagnosis is related to a paucity of intraabdominal fat often seen in pediatric patients and patients with a lean body habitus.(127–130) Optimal cecal opacifica- tion and distention are important because without cecal opaci- fication a distended appendix can be mistaken for a small-bowel loop.(131, 132) Therefore, intravenous, oral, and rectal contrast should be used. Appendicitis may cause reactive dilatation of the small bowel and mimic a small-bowel obstruction, resulting in a missed diagnosis of the underlying problem. In addition, the dilated small bowel impedes the flow of oral contrast, so that opacification of the cecal region is suboptimal, creating difficulty in diagnosis. Therefore, a small-bowel obstruction in patients who have no history of surgery or cause for obstruction is suspi- cious for appendicitis, especially in younger patients.(130) Mucocele and Tumors of the Appendix Mucocele refers to distension of all or a portion of the appendix with mucus secondary to obstruction by appendicolith, adhesions, or tumor.(133) Most commonly, this lesion is a retention mucocele and is asymptomatic (Figure 11.31). Some cases are caused by muci- nous cystadenomas or cystadenocarcinomas of the appendix.(133, 134) Continued secretion of mucus produces a large (up to 10 cm), well-defined, cystic mass in the right lower quadrant, which may have a thin rim of wall enhancement or calcification.(135) Rupture of the mucocele may result in psuedomyxoma peritonei causing gelatinous implants and mucinous ascites throughout the peritoneal cavity. Although an enhancing nodular component is concerning for malignancy (136), neoplastic and retention mucoceles cannot be reliably distinguished by imaging studies. Adenocarcinoma of the appendix is rare and is usually discovered in the clinical setting of suspected appendicitis in an older adult. Imaging demonstrates a soft tissue mass within or replacing the appendix.(133) Lymphoma of the appendix appears similar to appendicitis, but is typically larger with a diameter of 3 cm or greater.(137) Carcinoid is the most common tumor of the appendix accounting for 85% of all tumors.(133) Carcinoid of the appen- dix usually appears as a focal enhancing mass in the distal appendix.(133, 138) Carcinoid metastases to mesentery and the liver enhance brightly on arterial phase imaging because of their vascularity.(138–146) Three-dimensional CT angiography is useful to fully appreciate the mesenteric mass and its relation- ship to the vessels, which is important for surgical planning. (140–147) In addition to the liver, metastases can be seen on CT in the lung and bones. Other Tumors of the Colon CT remains the imaging study of choice for detection of benign and malignant tumors of the colon other than adenoma and Figure 11.31 Appendix Mucocele. Axial MDCT demonstrates distension of the appendix with mucus. Figure 11.32 Lipoma. Axial MDCT demonstrates a 2–3 cm, round, sharply defined tumor with homogenous fat density (-80 to -120 H) adherent to the sigmoid colon. 1 limitations of colorectal imaging studies adenocarcinoma. Metastases to the colon can be seen on con- trast enhanced MDCT, if they are large enough; but CT cannot differentiate primary tumor from metastasis.(148) One of the most common benign colonic tumors is a lipoma. Lipomas can be easily diagnosed by demonstrating a 2–3 cm, round or ovoid, sharply defined tumor with homogenous fat density (-80 to -120 H) (Figure 11.32). Colonic lymphoma usually appears as either a marked thicken- ing of the bowel wall that often exceeds 4 cm, or a homogeneous soft-tissue mass without calcification. Lymphoma characteristi- cally causes much larger soft-tissue masses than adenocarcinoma. Owing to the softness of the tumor, the lumen is commonly dilated or normal, rather than constricted, and bowel obstruction is uncommon. The absence of desmoplastic reaction and diffuse lymphadenopathy help to differentiate lymphoma from adeno- carcinoma.(149–150) Gatrointestinal Stroma Tumors (GIST) can be benign or malignant and cannot be diffentiated on cross sectional imaging without distant metastases to the liver or peritoneum.(151) GISTs can appear as an exophytic or intraluminal mass, and size var- ies from millimeters to 30 cm. Cystic degeneration, hemorrhage, and necrosis are common in large lesions with calcification rarely noted (Figure 11.33). The tumor cavity may communicate with the colon lumen and contain air or oral contrast. Sarcomas that arise in the bowel, anorectum, or omentum are indistinguishable from malignant GIST.(151) Tissue types include leiomyosarcoma, fibrosarcoma, and liposarcoma. Sigmoid and Cecal Volvulus Diagnosis of large bowel volvulus is usually made by plain radio- graphs or fluoroscopy, but CT is used to detect evidence of isch- emia. Sigmoid volvulus is seen on CT as distended colon with the mesenteric twist appearing as a “whirl.” Cecal volvulus has a similar appearance with the apex of the distended colon pointed toward the right lower quadrant and the “whirl” of cecal mesentery in the right abdomen. The axis of torsion is in the ascending colon above the ileocecal valve. Signs of bowel ischemia include benign wall thickening, “thumbprinting”, inflammation of pericolic fat, and pneumatosis (air in the bowel wall).(152) Small Bowel Obstruction Accuracy of Diagnosis and Causes of SBO CT has gained favor as the initial radiologic examination of patients with SBO because it can often determine the cause, severity, and transition point of obstruction.(153–158) The sen- sitivity of CT for high-grade SBO is 90–96%, with a specificity of Figure 11.34 Small Bowel Obstruction. Axial MDCT demonstrates multiple dilated loops of small bowel with air fluid levels. Intraluminal fluid distends the bowel and acts as a natural contrast agent. Figure 11.33 GIST. Axial MDCT demonstrates a large heterogenous exophytic mass with cystic degeneration and necrosis that communicates with the lumen of adjacent colon and small bowel. Figure 11.35 SBO from Adhesions. Axial MDCT of same patient in Figure 11.II- L-1 shows abrupt transition from dilated to nondilated bowel suggests adhesions as the cause. A suture line from the patient’s colonic resection and ileocolonic anastomosis is seen. 11 improved outcomes in colon and rectal surgery 91–96%.(153, 157, 159–165) The 3, 6, and 9 rule can be used to detect bowel dilatation on CT scans. Oral contrast is not always necessary as the intraluminal fluid distends the bowel and acts as a natural contrast agent (Figure 11.34). Oral contrast should be avoided in patients with a high grade or complete SBO. Adhesions cause 50% to 75% of SBOs, but are often not directly visualized by CT. Beaklike narrowing or abrupt transition from dilated to nondilated bowel suggests adhesions as the cause (Figure 11.35). Obstruction from tumor, abscess, intussusception (Figure 11.36), inflammation, and hernia are readily diagnosed with CT. Paralytic/Adynamic Ileus Paralytic or adynamic ileus appears as dilation of small bowel without a transition zone. The colon may be distended or collapsed and this should not be mistaken for evidence of a tran- sition zone. CT is reported to be less accurate in patients with low-grade or partial SBO and it may be difficult to distinguish between a SBO and paralytic or adynamic ileus. In such cases the “small bowel feces” sign, which is gas bubbles mixed with particu- late matter in the dilated bowel, is a reliable indicator of a SBO. (161–166) If oral contrast reaches the colon, a complete SBO is not present. CT Enteroclysis CT enteroclysis is useful in the evaluation of equivocal cases, and is performed by placing a tube in the fourth portion of the duodenum with infusion of 1 to 1.5 L of dilute contrast into the small bowel. The addition of coronal reformations is a valuable adjunct to the transverse scans because it improves identification and exclusion of bowel obstruction.(167) Closed Loop Obstruction, Strangulation, and Intestinal Ischemia CT can diagnose closed loop obstruction of the small bowel and bowel ischemia. The “beak” or “whirl” sign may be seen at the obstruction and volvulus.(168) Dilated bowel loops with stretched and prominent mesenteric vessels converging on a site of obstruction suggest a closed loop obstruction. Decreased seg- mental bowel-wall enhancement and pneumatosis (Figure 11.37) are associated with small-bowel ischemia.(169) The diagnosis of small-bowel ischemia in the presence of obstruction has reported sensitivities varying from 75% to 100%, and specificities of 61%– 93%.(170–174) COMPUTED TOMOGRAPHIC COLONOGRAPHY (CTC) Colorectal Cancer Screening and the Advanced Adenoma Computed tomographic colonography (CTC) or Virtual Colon- oscopy is an excellent technique for the detection of colorectal polyps and cancer. Because colorectal cancer has an identifiable precursor lesion, the advanced adenoma (polyp), there is a gen- uine opportunity for prevention rather than detection alone. Figure 11.36 Ileocecal Intussusception. Axial MDCT CT demonstrates characteristic findings of the distal segment (intussuscipiens) dilated with a thickened wall. Its lumen contains an eccentric, soft-tissue mass (intussusceptum) with an adjacent crescent of fat density that represents the invaginated mesentery. Figure 11.37 Pneumatosis Intestinalis. Small bowel ischemia is suggested by the decreased segmental bowel-wall enhancement and pneumatosis intestinalis. Table 11.5 CTC laxative preparations. Laxative Agent Limitations Sodium Phosphate Because of rare reported instances of acute phosphate nephropathy, avoid use in elderly with hypertension, patients taking angiotensin-converting enzyme inhibitors, and patients with renal or cardiac insufficiency (184). Magnesium Citrate Avoid in severely compromised patients who cannot tolerate mild fluid or electrolyte shifts. Polyethylene Glycol (PEG) Most favorable safety profile but poorest adherence because of the consistency, taste, and large volume (4 L) that must be ingested. 111 limitations of colorectal imaging studies (216, 217) CTC’s sensitivity for polyp detection is similar to (175) or better than (176) double-contrast barium enema. CTC has accuracy similar to that of optical colonoscopy (OC) both in high-risk groups (177–180) and in a low-prevalence screen- ing population (181). Also, CTC has the potential to become an accepted technique for evaluation of the nonvisualized part of the colon after incomplete OC.(182) CT Colonography (CTC) Technique Adequate CTC software is critical for accurate interpretation, but even the best software system will fail if colonic preparation is inadequate. Colonic preparation involves a clear liquid diet the day before the exam and a laxative for catharsis.(183) The laxative for a standard CTC bowel preparation is sodium phosphate, which is used in nearly 90% of cases (Table 11.5).(183) Dilute barium is used to tag residual feces, and water soluble diatrizoate serves the dual purpose of uniform fluid tagging and secondary catharsis. (185) Gaseous distention can be achieved with room air or CO 2 , and the insufflations can be automated or manually controlled by the patient or the medical staff (technologist or physician). Both supine and prone axial scans are obtained with 3D software recon- structions. At least 8 to 16 detector CT is needed with 1.25 mm collimation (Figures 11.38 and 11.39). Benefits, Complications, and Limitations of CT Colonography (CTC) CTC does not involve the sedation or recovery time associated with OC. With the short scan time of MDCT scanners, patients must tolerate maximum inflation for only a few seconds, as opposed to OC and barium enema. A survey of patients undergoing colorec- tal cancer screening found that patients prefer CTC over OC and barium enema.(186) Unlike colonoscopy and barium enema, CTC allows visualization of organs outside the colon. Although nonen- hanced CTC (at one-fourth the standard radiation dose) is not adequate for screening, all solid abdominal and pelvic pathology, important disease such as abdominal aortic aneurysm, renal cell carcinoma, ovarian cancer, and other neoplasms can be detected. The most beneficial situation would be the discovery of an asymp- tomatic early process that could be cured with early treatment. The safety profile of CTC has been extensively reviewed. The largest U.S. study, the combined Working Group on Virtual Colonoscopy (187), found that CTC was a very safe, noninvasive procedure (Table 11.6) By combining the Working Group results with two other large multicenter studies (188–189), the total number of CTC examinations exceeds 50,000. None of the cases of perfora- tion from these three groups resulted in patient death. Many cases of CTC–related perforation have involved high-risk symptomatic patients for whom OC was either incomplete or contraindicated. No cases of symptomatic perforation resulted from patient-con- trolled insufflations or automated CO 2 delivery. Staff-controlled manual insufflations lack the inherent safeguards of the other two methods and have accounted for virtually all known cases Figure 11.38 Normal CTC Supine Axial 2D Images. Figure 11.39 Normal CTC 3D Image of the Colon. Table 11.6 Working group on virtual colonoscopy experience (187) — (21,923 CTC performed between 1997 and 2005). Screening CTC (11,707 patients) Diagnostic CTC (10,216 patients) No cases of perforation 2 cases of perforation (1 asymptomatic, 1 symptomatic) Note: Overall complication rate of 0.02% Symptomatic perforation rate of 0.005% (one in 21,923 patients). The 1 patient in 21,923 with a symptomatic perforation was a patient with known annular carcinoma of the sigmoid colon who was already symptomatic prior to CTC, and massive pneumoperitoneum was found after a few puffs of air were delivered.(187) 11 improved outcomes in colon and rectal surgery of symptomatic perforation. The risk of perforation with auto- mated or patient-controlled distention methods approaches zero among asymptomatic adults.(190) The automated CO 2 delivery is not only safe but also results in improved colonic distention and reduced spasm.(191) Although the capability of CTC to depict polyps is both opera- tor and technique dependent, this modality has a relatively high specificity.(176, 178–181) Some of the inconsistent results in pre- vious studies have been attributed to reader inexperience, inap- propriate protocol, and lack of image software technology. CTC trials involving cohorts with protocols restricted to a primary 2D approach fared poorly (192–194), whereas those that relied on 2D and 3D polyp detection performed well (178–181, 195). Primary CT Colonography Screening with Selective Optical Colonoscopy CTC cannot replace optical colonoscopy (OC), as it is an essential diagnostic tool for the nonsurgical removal polyps. As a screening test applied to asymptomatic adults; however, OC is a relatively invasive procedure, with reported perforation rates of 0.1–0.2%. (196–200) Given that a small minority of screening patients actu- ally harbors a clinically relevant lesion (181, 201–206), the high rate of negative screening studies may come into question now that a less invasive alternative, CTC, is becoming widely available and greatly improved from the past. Therefore, primary CTC with selective OC deserves consideration as a preferred screening strat- egy. In this approach patients are screened with CTC and patients with polyps >10 mm are offered same-day OC with polypectomy. Patients with polyps 6 to 9 mm are given the option of CTC sur- veillance or OC with polypectomy. To avoid any confusion, or anxiety, potential diminutive lesions ( ≤ 5 mm) are not reported. In a large screening study of asymptomatic adults by Kim et al. (195) (Table 11.7) found that CTC and OC screening methods resulted in similar detection rates for advanced neoplasia within the same general population. The results of this study also sug- gest that a 10 mm threshold for polypectomy at asymptomatic screening would probably capture the vast majority of clinically relevant lesions. The study noted scarcity of small advanced neoplastic lesions and marked decrease in the use of OC and total rates of polypectomies in the CTC group (Table 11.7); which suggests that this screening approach is a safe, clinically effective, and cost-effective filter for therapeutic OC.(195) Markov modeling of large cohorts has also shown that the strategy of not reporting diminutive polyps (<5 mm) during CTC screening is a cost-effective approach that can substantially reduce the rate of polypectomy and complications without any sacrifice with respect to cancer prevention.(204) However, the clinical management of polyps 6 to 9 mm that are detected during CTC is controversial. One approach is to offer OC for polypectomy to all patients with polyps >6 mm.(207) An option of short-term CTC surveillance for patients with one or two small CTC-detected polyps has also been suggested.(208) Potential benefits include the decreased use of resources, procedural risks, and cost. Potential drawbacks are the possibility of following a polyp that harbors a focus of cancer. Ultimately, more investigation will be needed to determine which strategy is more beneficial for polyps <10 mm that are found during CTC. Furthermore, by combining CTC and OC screen- ing efforts, the overall screening compliance could substantially increase.(192) CT Colonography Follow-Up after Surgery for Colorectal Cancer More than half of colorectal cancer recurrences are distant metas- tases to the liver and lungs (209, 210) and most local recurrences lack an intraluminal component (210). CTC is usually performed without IV contrast for screening, but CTC performed with IV contrast enhancement could accomplish the dual function of annual CT surveillance of the abdomen and liver, as well as examination of remaining colonic lumen. CTC could also have a role in postsurgical patients in whom optical colonoscopy has failed or in patients with a colostomy. The limitations of CTC in the postoperative patient include extrusion of surgical staples, inflammatory polyps, and benign ulcers. Extruded staples can be clearly distinguished from true polyps on 2D images by their high attenuation.(211) Because inflammatory polyps and benign ulcers are not distinguishable from adenomatous polyps on CTC, follow-up OC and biopsy will be needed.(211) Nevertheless, it would be efficient if CTC could eliminate through screening those patients whose colon is normal, while also performing the dual function of evaluating the entire abdomen for metastatic disease. Also, the ability of IV contrast enhanced CTC to provide images of the bowel wall, extracolonic tissues, lymph nodes, and liver in one setting may provide a more accurate preoperative staging of colorectal cancers.(212, 213) A recent study found that CTC colorectal cancer T staging overall accuracy was 73–83%, and N staging was associated with an overall accuracy of 80%. (214) Thus, contrast-enhanced CTC is a fairly accurate technique for preoperative staging of colorectal tumors.(212, 213) FLOUROSCOPY Barium Enema Single and Double Contrast Barium Enema (DCBE) Single Contrast Barium Enema is performed by filling the rectum and colon with barium through an enema catheter after inflat- ing a retention rectal balloon. Double Contrast Barium Enema (DCBE) or Air Contrast Barium Enema (ACBE) is performed similarly, except the colon is partially filled with undiluted Table 11.7. Results from Kim et al.(195) Variable Primary CTC (n = 3,120) Primary OC (n = 3,163) Use of OC 246 3,163 # of Advanced Adenomas >10 mm 103 103 6–9 mm 5 11 <5 mm 1 3 Invasive Carcinoma 14 4 Note: Only 3 subcentimeter polyps with high-grade dysplasia (0.05%), and there were no subcentimeter cancers. Total of 2,006 polypectomies to remove diminutive polyps (<5 mm), which yielded only 4 advanced lesions (0.2%). 11 limitations of colorectal imaging studies barium. Once the barium reaches the middle transverse colon, the enema bag is lowered to the floor and the rectum is drained by gravity. Using a pneumatic bulb, room air is insufflated into the colon. The radiologist manipulates the amount of air insufflated; and analyzes the barium-coated mucosal surface to detect abnor- malities. Fluoroscopic guidance allows the radiologist to opti- mize technical components. Afterwards, overhead radiographs are obtained in projections that the radiologist cannot obtain at fluoroscopy. Both single and DCBE can identify malignant stric- tures, but the double contrast of air and barium provides better visualization of the mucosa and colon polyps.(215) The radio- graphic appearance of the lesion depends on the profile in which the lesion is imaged and the location of the lesion relative to the barium pool. It is not possible to distinguish between the sporadic adenomatous polyps and polyposis syndromes using contrast studies.(216) The appearance of polyps and early cancers can be sessile, polypoid pedunculated, or carpet lesions. Colorectal carcinomas may manifest as polypoid, semiannular, or annular strictures. Annular strictures are characterized by circumferential narrowing of the bowel, with overhanging borders referred to as “apple core” lesions (Figure 11.40). Benign strictures from isch- emic, infectious, and inflammatory processes, in contrast, tend to have smooth, tapering borders. The positive predictive value for malignant strictures on DCBE is 96% (sensitivity, 63–66%) and the positive predictive value for benign strictures is 84–88% (sen- sitivity, 88–86%, respectively).(217) On occasion, however, the area of narrowing in diverticulitis may have more abrupt borders and may mimic the appearance of tumor. If the barium enema examination reveals equivocal findings, colonoscopy should be performed after treatment for diverticulitis to rule out an under- lying carcinoma. When annular carcinomas are nonobstructive, it usually is possible to perform DCBE so that the colon may be evaluated for other synchronous neoplasms. Performance of DCBE should not be performed in patients with large bowel obstruction, acute colitis, or when there is concern for bowel per- foration, as barium can cause peritonitis. In these situations, a water-soluble contrast agent should be used.(216) Limitations of Double Contrast Barium Enema (DCBE) DCBE is a valuable tool in colorectal cancer screening, but the examination is not without limitations. When lesions are missed, both perceptive/interpretive and technical errors are responsible. (218, 219) Perceptive/interpretive errors occur when lesions are overlooked because of superimposed bowel loops or are hidden by deep haustral folds. Also, polyps that are small and flat or that directly abut a haustral fold may be subtle. Another area that may pose perceptive diagnostic difficulties is the ileocecal valve. While some carcinomas arising at the ileocecal valve may be obvious polypoid lesions, others may manifest as relatively subtle splay- ing or distortion of the valve.(220) Incompetence of the ileocecal valve can degrade the quality of barium enemas by preventing full colonic distention and allowing the small bowel to obscure segments of the colon. Internal hemorrhoids appear either as thickened, undulating folds that extend 3 cm or less from the anorectal verge or as a cluster of small submucosal nodules that has been likened to the appearance of a bunch of grapes.(221) In many cases, internal hemorrhoids can be diagnosed confidently on the basis of the radiographic findings. On occasion, however, large or thrombosed hemorrhoids can mimic the appearance of tumor, whereas rectal carcinomas that infiltrate the submucosa can mimic the appear- ance of hemorrhoids.(221, 223) Digital rectal examination and/ or proctoscopy therefore should be performed whenever the radiographic findings are equivocal. Technical errors occur due to poor bowel preparation and adherent stool can be difficult or impossible to differentiate from true polypoid lesions. Regimens to prepare the colon are similar to CTC and OC. Scout images are taken before the study and if stool is seen in the colon a rescheduled barium enema examina- tion may be performed after more rigorous bowel preparation. DCBE are a fairly safe procedure, but the referring physician should state if a recent endoscopic intervention has been per- formed. There should be a 1-week interval between barium enema examination and performance of large-forceps biopsy through a rigid sigmoidoscope, snare polypectomy, or hot biopsy; because these endoscopic interventions may tear the colonic mucosa and result in a small risk of perforation. Performance of a small- forceps biopsy through a flexible sigmoidoscope or colonoscope does not preclude performance of barium enema examination on the same day.(224, 225) DCBE has been exhaustively reviewed, usually retrospectively. DCBE has a sensitivity of 70% for polyps >7 mm (226–229) and a sensitivity of 81–95% in detecting polyps >1 cm in diameter (226–228). The detection rate for colorectal cancer or malignant stricture ranges from 70% to >96% (230–232). The American Cancer Society guideline for colorectal cancer screening includes DCBE examinations at 5- or 10-year intervals for patients with average risk and older than 50 years of age.(233) In conclusion, DCBE can be used to detect most polyps (>10 mm) that are at Figure 11.40 Annular Carcinoma. DCBE demonstrates an annular “apple core” stricture characterized by circumferential narrowing of the bowel with mucosal destruction and shelf-like, overhanging borders. 11 improved outcomes in colon and rectal surgery risk for malignant degeneration and provides an invaluable pub- lic service by helping to lower the mortality rate due to colorectal cancer.(234) Ulcerative Colitis Barium enema can be used to confirm the diagnosis of UC, to dif- ferentiate it from Crohn’s disease/colitis, and to assess the extent and severity of disease. The radiographic appearance of UC depends on the state of the disease process.(216) Early in the dis- ease, the mucosa is stippled with barium adhering to the conflu- ent, superficial ulcers. Collar button ulcers are deeper ulcerations of thickened edematous mucosa with crypt abscesses extending in the submucosa. As the ulcerations enlarge, inflammatory psue- dopolyps (islands of residual mucosa) and inflammatory polyps (islands of inflamed mucosa) appear as irregular projections into the bowel lumen. Late in the disease (Figure 11.41), there is blunt- ing of the haustral markings with a narrow tubular appearance to the colon, referred to as a “lead pipe colon”.(216) The terminal ileum is usually normal, but rare backwash ileitis may produce an ulcerated and patulous terminal ileum. Barium contrast studies are not able to distinguish UC associated polyps from adenoma- tous polyps or dysplasia; and UC associated cancers tend to be flat or infiltrating and do not always appear as typical neoplasms. Therefore, contrast enemas are not recommended for routine surveillance.(216) Crohn’s Disease and Crohn’s Colitis The appearance of Crohn’s disease in the small bowel and the colon is similar (Table 11.8). Shallow, 1 to 2 mm depressions usu- ally surrounded by a well-defined halo, called aphthous ulcer- ations, are the earliest mucosal lesions seen in Crohn’s disease. (235) Other hallmarks are: (1) thickened and distorted folds; (2) fibrosis with thickened walls, contractures, and stenosis (Table 11.3). Fibrosis and progressive thickening of the bowel wall narrow the lumen producing the “string sign” in the terminal ileum (Figure 11.42). Pseudodiverticula of the colon are formed by symmetric fibrosis on one side of the lumen, causing saccu- lar outpouchings on the other side. Deep ulcerations are larger and often linear, forming fissures between nodules of elevated Figure 11.41 Ulcerative Colitis Late in the Disease. DCBE demonstrates blunting of the haustral markings with a narrow tubular appearance of the sigmoid colon, referred to as a “lead pipe colon”. Table 11.8 Small Bowel Studies. Examination Technique Benefits and Limitations Small Bowel Follow Through (SBFT) Patient drinks barium while a series of supine abdominal films are obtained until the terminal ileum and cecum are filled. Demonstrates the mucosal surface, but is insensitive; and limited by overlap of bowel loops, poor distension, and intermittent filling. Small Bowel Enteroclysis This study provides more uniform distension of the bowel, even distribution of barium, superior anatomic detail, and shorter overall examination time. Figure 11.42 Crohn’s Disease “String Sign”. Small bowel follow through demonstrates fibrosis and progressive thickening of the bowel wall that narrows the terminal ileum, producing the “string sign”. 11 limitations of colorectal imaging studies edematous mucosa (“cobblestone pattern”). Contrast enemas are better than colonoscopy at identifying and characterizing fistulas, strictures, and the distribution of disease.(236) Diverticulosis and Diverticulitis Diverticula are often seen on barium enema examinations, as barium or gas-filled sacs outside the colon lumen. Barium enema examination is considered safe for diverticulitis, except when signs of free intraperitoneal perforation or sepsis are present. Diverticulitis appears as deformation of the colon wall in asso- ciation with diverticular sacs (Figure 11.43), and occasionally extravasation of barium outside the colon lumen. Abscess can cause extrinsic mass effect on the adjacent colon and barium can leak into the abscess cavities. A colovesical fistula is the most common diverticular associated fistula, but contrast enemas are able to make the diagnosis only 20% of the time.(237) Colonic Lymphoma, Submucosal, and Extracolonic Lesions Lymphoma can appear as small or large nodules, which may ulcerate and perforate. Diffuse infiltration of the bowel wall results in bulbous folds and thickened bowel wall. In contrast to primary colorectal cancer, narrowing of the lumen is uncom- mon, and dilation occurs when transmural disease destroys innervations. Endometriosis commonly implants on the sigmoid colon and rectum.(238) Defects are frequently multiple and of variable size. Barium studies demonstrate sharply defined defects that compress, but do not usually encircle the lumen. Benign pelvic masses such as ovarian cysts, cystadenomas, teratomas, and uter- ine fibroids produce smooth extrinsic mass impressions on the colonic wall, which is displaced but not invaded. Malignant pel- vic tumors and metastases involved with the colon often cannot be differentiated from primary tumors by imaging methods, and Crohn’s disease may look similar. Lipomas appear as a smooth, well-defined, round filling defect, usually 1 to 3 cm in diameter. The tumors are soft and change shape with compression.(239) (CT can confirm. See CT scan: other tumors of the colon). Water-Soluble Contrast Enema Volvulus and Intussusception Sigmoid volvulus appears as obstruction that tapers to a beak at the point of the twist, usually approximately 15 cm above the anal verge. Mucosal folds spiral into the beak at the point of obstruc- tion. Cecal volvulus appears as a beak like or twisted termination at the point of obstruction in the ascending colon with a dilated cecum high in the abdomen (Figure 11.44). Ileocoloc and colocolic intussusception on contrast studies demonstrate barium trapped between the intussusceptum and the receiving bowel, forming a coiled-spring appearance. Postoperative Complications and Anastomotic Assessment Water-soluble contrast enemas are frequently used postop- eratively to examine a colocolic, colorectal, coloanal, or ileal— anal anstomosis.(240) The studies are performed by retrograde Figure 11.43 Divertivulitis. Barium enema demonstrates a deformed colon wall with diverticular sacs. Figure 11.44 Cecal Volvulus. Water soluble contrast enema demonstrates a beak like termination at the point of obstruction in the ascending colon with a markedly dilated cecum seen high in the abdomen. 11 improved outcomes in colon and rectal surgery Figure 11.46 Anastomotic stricture. Small bowel follow through and water soluble contrast enema demonstrate an ileal pouch–anal anastomotic stricture. Figure 11.45 Anastomotic Leak. Water soluble contrast enema shows extravasation of contrast into the presacral space. Figure 11.47 Normal Defecogram. Lateral radiograph is obtained with the patient in a neutral position after a thick barium paste is placed into rectum. Figure 11.48 Anorectal Angle. The anorectal angle is created by the intersection of the long axis of the anal canal and a line drawn along the posterior wall of the rectum. 11 limitations of colorectal imaging studies administration of a water-soluble contrast under the weight of gravity or by direct hand injection via a catheter inserted into the anal canal. Radiographic findings of an anastomotic leak include the extravasation of contrast freely into the peritoneal cavity or into a contained cavity (Figure 11.45). Water-soluble contrast enema is more sensitive than CT with rectal contrast.(240) Total proctocolectomy and ileal pouch—anal anastomosis (Figure 11.46) complications include anastomotic stricture.(241–244) Some studies have cited an anastomotic diameter of 8 mm or less as the threshold value for diagnosing strictures that may need dilatation procedures before ileostomy closure.(245) Physiologic Examinations Chronic constipation and incontinence are common complaints with many possible etiologies. Multiple examinations are avail- able to assess the physiology of the lower GI tract, including defecography, anorectal manometry, balloon proctography, and colon transit studies. Defecography Defecography (evacuation proctography) is a dynamic evalua- tion of the anatomy and mechanics of defecation. A thick bar- ium paste is deposited within the rectum. Static lateral images are obtained with the patient in a neutral, anal contraction, and straining position. Fluoroscopic video is then obtained during the act of defecation. The static images allow measurement of the anorectal angle, the angle created by the anal canal, and posterior wall of the rectum (246) (Figure 11.47 and 11.48). As the patient defecates, the anorectal angle should straighten and approach 180 degrees. Abnormally high or low anorectal angles suggest a mechanical cause for the patient’s constipation. The length that the anorectal junction descends during defecation can be mea- sured as well. An abnormal length of descent (>5 cm) of the ano- rectal junction can be a source of pudendal nerve damage and, if chronic, incontinence.(247) The most common abnormal- ity detected by defecogram is a rectocele. A rectocele is an out- pouching of the rectum, usually along the anterior wall. Retained barium in the rectocele can document incomplete rectal evacua- tion. In severe cases of rectoceles, internal rectal prolapse can be observed by defecogram. A negative defecogram can exclude such conditions as enteroceles, sigmoidoceles, rectal prolapse, rectal intussusception, puborectalis muscle dysfunction, and postero- lateral pouches. Colorectal Transit Colorectal transit times can be documented by having the patient ingest a barium meal and obtaining serial abdominal radio- graphs. All the barium should be cleared in a normal patient in 4 days. Retained barium after 4 days confirms delayed colorec- tal transit time.(248) An alternative method utilizes radiopaque rings (Sitzmarkers ® , Konsyl Pharmaceuticals, Ft Worth, TX) to assess colonic transit time. Twenty four markers are ingested. The patient is instructed not to use enemas, laxatives, or supposito- ries for 5 days. Radiographs are obtained daily or on days 1, 3, and 5.(249) Eighty percent of the markers should pass in 5 days and all of the markers normally pass by the seventh day.(246, 248) The diagnosis of colonic hypomotility/inertia is suggested if there is delayed transit time and the markers are scattered evenly throughout the colon. A functional outlet obstruction, such as rectal prolapsed or anismus, is suggested if there is delayed transit time with clustering of the radiopaque markers in the rectosig- moid colon.(246) Anorectal Manometry and Balloon Proctography Anorectal manometry is performed to assess rectal sensation and motor function. The rectum is distended by a balloon. The nor- mal response to rectal distention is contraction of the external anal sphincter and relaxation of the internal anal sphincter. Loss of this reflex can be detected by anorectal manometry and can be seen in Hirschsprung’s disease or severe idiopathic constipa- tion.(249) Balloon proctography is a similar examination where the rectal balloon is filled with a contrast material, allowing visu- alization of the rectum. Visual assessment of the rectum with calculation of the anorectal angle can be performed in addition to measurement of the anorectal pressure.(248) Some studies suggest that balloon proctography is less sensitive than defec- ography in detecting certain anatomic abnormalities, including rectoceles. ULTRASONOGRAPHY (US) Transabdominal Ultrasound and Intraoperative Ultrasound (IUS) Ultrasonography (US) utilizes sound waves to provide real time imaging of the body. A transducer is placed on the patient that not only generates sound waves (of a single frequency) but also detects the reflected echoes. US can successfully image solid visceral organs and fluid filled structures. US is superb at differ- entiating between cystic and solid structures, and is frequently Figure 11.49 Appendicitis. Axial view of the appendix reveals a thickened and hypoechoic wall. An appendicolith is represented by the hyperechoic material seen within the lumen (arrow). . cause. A suture line from the patient’s colonic resection and ileocolonic anastomosis is seen. 11 improved outcomes in colon and rectal surgery 91–96%.(153, 157, 159–165) The 3, 6, and 9 rule can. 1 improved outcomes in colon and rectal surgery (CTA) has become the method of choice for imaging the pulmo- nary vasculature, and has replaced invasive pulmonary angiog- raphy. borders. 11 improved outcomes in colon and rectal surgery risk for malignant degeneration and provides an invaluable pub- lic service by helping to lower the mortality rate due to colorectal cancer.(234) Ulcerative