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Imaging Evaluation of Complications at Optical Colonoscopy
Imaging Evaluation of Complications at Optical Colonoscopy David H. Kim, MD,a Perry J. Pickhardt, MD,a Andrew J. Taylor, MD,a and Christine O. Menias, MDb
Optical colonoscopy (OC) is an essential component of colorectal cancer screening. In addition to favorable polyp detection capabilities, OC has a unique therapeutic role with the ability to remove identified polyps. However, this procedure carries a low but real risk for morbidity and mortality. OC requires physical intubation of the length of the colon and manipulation of the instrument. In addition, the performance of therapeutic polyp removal increases risk. Inherent to this procedure are several pathways for potential adverse events. Complications can be divided into several major categories including perforation, hemorrhage, postpolypectomy syndromes, and issues related to sedation. The imaging manifestations of complications related to optical colonoscopy as well as the potential underlying mechanisms will be reviewed. Emphasis will be placed on cross-sectional imaging given the improved sensitivity and specificity over conventional radiography.
Optical colonoscopy (OC) is a valuable tool in the detection of colorectal neoplasia and the prevention of cancer. Given its favorable performance characteristics for polyp detection and unique therapeutic ability, OC will undoubtedly remain an essential component of colorectal screening. However, this procedure carries a low but real risk for morbidity and mortality. OC requires physical intubation of the length of the colon and manipulation of the instrument. In addition, the performance of therapeutic polyp removal increases risk. Inherent to this procedure are several pathways for potential adverse events. Complications can be divided into several major categories including perfoFrom the aDepartment of Radiology, University of Wisconsin Medical School, Madison, WI; and bMallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO. Reprint requests: David H. Kim, MD, Department of Radiology, University of Wisconsin Medical School, E3/311 Clinical Science Center, 600 Highland Ave., Madison, WI 53792-3252. E-mail: [email protected]. Curr Probl Diagn Radiol 2008;37:165-77. © 2008 Mosby, Inc. All rights reserved. 0363-0188/2008/$34.00 ⫹ 0 doi:10.1067/j.cpradiol.2007.10.004
Curr Probl Diagn Radiol, July/August 2008
ration, hemorrhage, postpolypectomy syndromes, and issues related to sedation. This review demonstrates the radiologic imaging manifestations of various colonoscopic complications including some rare and unusual complications related to this procedure. Emphasis will be placed on computed tomographic (CT) evaluation given its increased sensitivity and increased characterization of suspected OC complications over conventional radiography.
Perforation Perforation may occur from one of two pathways in the absence of therapeutic procedures. One recognized mechanism involves pneumatic distension with barotrauma. Colonoscopy can generate wall pressures of up to 140 mm Hg, which has been shown to create colonic tears in animal and cadaveric studies.1 Typically, the tears involve the serosal layer along the longitudinal axis of the colon. This allows herniation and thinning of the mucosa through these tears, ultimately leading to a perforation. As predicted by LaPlace’s law where pressure is proportional to diameter, the capacious nature of the cecum is a frequent location from these types of tears.1 Such perforations can lead to massive amounts of free air.2 The second and perhaps more common manner of perforation is related to mechanical trauma from the endoscope either by direct injury from the end of the scope or by an abrasive injury from the side of the scope as it is pushed forward. Maneuvers such as straightening the sigmoid colon and the slide-by maneuver also increase the risk for perforation. These injuries typically occur in the sigmoid colon and left colon.3,4 At therapeutic colonoscopy, the performance of polyp removal adds another possible mechanism for perforation related to a through-and-through injury of the colonic wall. Polypectomies significantly increase risk for perfora-
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FIG 1. A 66-year-old female undergoing screening colonoscopy complicated by sigmoid perforation. (A-C) Note the extraperitoneal location of air on these three transverse images despite rupture of an intraperitonealized colonic segment. Air has tracked back along the sigmoid mesentery and then dissects cephalad up the retroperitoneal fascia planes (arrows). (D) CT colonography performed 6 months later to complete screening demonstrates a 17-mm sigmoid polyp. Therapeutic OC with polypectomy revealed an advanced tubular adenoma. (Color version of figure is available online.)
tion in comparison to colonoscopic exams without polypectomy.5 The location of perforation is related to the location of the polypectomy as would be expected. Although the overall perforation rate at OC is relatively low, ranging widely from 0.3 to 3 cases per 1000 examinations,3,4,6-8 it is a serious complication that often requires surgical intervention. The radiologic imaging findings of colonic perforation resulting from OC are dependent on the location of injury. Perforations of intraperitoneal colonic seg-
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ments on a mesentery including the transverse colon, sigmoid colon, and cecum will more often lead to free intraperitoneal air and fluid, whereas perforation of the ascending colon, descending colon, and rectum are more likely to result in extraperitoneal air and fluid. However, it is important to note that perforation of intraperitoneal colonic segments can often result in only extraperitoneal air when contained within its supplying mesentery (eg, the sigmoid mesocolon) (Fig 1).
Curr Probl Diagn Radiol, July/August 2008
FIG 2. Cecal perforation following OC. (A and B) Two transverse CT images demonstrate extravasation following perforation. There are small amounts of fluid adjacent to the right colon (arrow) as well as fairly large amounts of extravasated contrast layering dependently in the pelvis (arrowhead).
When the colon is perforated at an intraperitoneal portion, there is free leakage of air and often fluid into the peritoneal cavity. While upright or decubitus abdominal radiographs can detect small amounts of free intraperitoneal air, it is important to note that supine radiographs are fairly insensitive until relatively large amounts of intraperitoneal air are present, with demonstration of increased lucency over the liver and visualization of the serosal surface of the bowel wall (Rigler’s sign).9 In addition, conventional radiographs are insensitive to the presence of fluid. On the other
Curr Probl Diagn Radiol, July/August 2008
FIG 3. Extraperitoneal perforation following rectal polypectomy. (A) Abdominal radiograph is grossly negative following this subtle perforation. (B) Transverse CT image clearly demonstrates small amounts of extraluminal air (arrow), which remains in an extraperitoneal location as the perforation occurred below the peritoneal reflection. Note the value of CT and relative insensitive nature of radiographs for small extraperitoneal perforations.
hand, CT can readily detect small amounts of both free intraperitoneal air and fluid. When extraluminal fluid is present, it tends to collect in dependent portions such as the hepatorenal fossa (Morrison’s pouch), the paracolic gutters, the mesenteric root, and in the pelvis
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(Fig 2). In some cases, there may be foci of extraluminal gas congregating near the perforation site, which may hint at its location.10 Air may also be seen locally tracking within the bowel wall (pneumatosis coli). When the perforation at OC primarily results in extraperitoneal gas without pneumoperitoneum, the radiographic presentation is markedly different. In this situation, extraluminal air dissects from the site of colonic perforation within the subperitoneal space contained by peritoneal ligaments and mesenteries, as well as tracking along extraperitoneal and retroperitoneal fascial planes.11 In our experience, this situation is more frequent than frank pneumoperitoneum. CT is much more effective in the diagnosis compared with conventional radiography, where detection of smaller amounts of extraperitoneal gas can be very difficult (Fig 3). As the amount of extraperitoneal air increases, these collections may coalesce into large pockets that exert mass effect on adjacent abdominal organs. Gas may eventually extend into the peritoneal cavity, resulting in secondary pneumoperitoneum (Fig 4). Subperitoneal gas may also track into the mediastinum and even result in subcutaneous emphysema in the neck and chest (Fig 5). Colonoscopy (with or without polypectomy) may also lead to dissection of air within the wall of the colon or pneumatosis. The exact mechanism is unknown but may be related to mucosal injury and increased intraluminal pressure.12 Pneumatosis coli typically presents as submucosal lucent collections within the wall at CT. Colonic pneumatosis can be fairly extensive and then be identified at conventional radiography. The air may dissect into the mesenteric venous system and into the portal veins. This can lead to foci of air trapped within the periphery of the liver within small portal venous branches (Fig 6). Colonic perforation at OC may present acutely with peritonitis or subacutely with abscess formation. Bacterial seeding of parenchymal organs is a consideration in this clinical situation when the patient demonstrates persistent fevers (Fig 7). When imaging is indicated, CT is clearly favored over conventional radiography. Although OC-related injuries occur in the setting of a “prepared” colon, the incidence of local and diffuse soiling is high. One study found local soiling in 48% of cases and diffuse feculent material in 21% of cases at exploratory laparotomy.3 Although nonsurgical management may be initially pursued in a small subset of patients who are hemodynamically stable with no
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FIG 4. Rectal perforation following OC. (A-C) Three selected transverse CT images demonstrate extraperitoneal perforation with subsequent extension into the peritoneal cavity. Note the free intraperitoneal air accumulating anterior to the liver (arrow).
Curr Probl Diagn Radiol, July/August 2008
FIG 5. An 81-year-old female who underwent diagnostic OC for melana. Ninety minutes after the procedure, she experienced abdominal pain and facial crepitus. (A and B) Transverse CT images demonstrate extensive retroperitoneal air, which extends up the chest to the neck, related to this colonic perforation. (C) Digital scout nicely depicts the extensive subcutaneous extension of air.
FIG 6. Pneumatosis coli and portal venous gas following colonoscopy. (A and B) Transverse CT image (A) demonstrates multiple lucencies in the colonic wall in the right colon consistent with pneumatosis (arrow). CT image (B) through the liver demonstrates scattered portal venous gas trapped in tiny peripheral venous branches (arrowheads).
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FIG 7. Subacute sequelae from colonic perforation. (A-C) CT images (A and B) demonstrate a pericolonic abscess (arrows) noted several days after screening OC. Patient presented with shaking fever and chills. Contrast injection (C) of subsequently placed abscess drain demonstrates the amorphous abscess cavity. The patient ultimately underwent a right hemicolectomy. (D) CT image of a different patient demonstrates a hepatic abscess (arrowhead) in a patient several days following screening OC with hepatic flexure polypectomy.
signs of peritonitis, prompt surgical treatment is favored in the majority of cases to decrease overall morbidity. In some cases with subacute presentation, image-guided abscess drainage may be indicated before definitive surgical intervention. In cases where colorectal evaluation at OC is incomplete due to perforation (or any other cause
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for that matter), it is important to eventually complete the evaluation after the complication is resolved. CT colonography (also referred to as virtual colonoscopy) represents an excellent minimally invasive means for evaluating the proximal colon in cases where the endoscope at OC fails to reach the cecum (Fig 8).
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FIG 8. Incomplete screening OC in a 74-year-old female. (A) Abdominal radiograph with massive free air from an incomplete screening colonoscopy to the sigmoid colon complicated by perforation. Surgical repair (segmental sigmoid resection with primary anastomosis) was required. (B-D) Transverse 2D (B) and 3D (C) images demonstrate one of two unsuspected annular carcinomas (arrows) identified at CT colonography performed 16 months later to complete screening. OC image (D) confirms the mass. (Color version of figure is available online.)
Hemorrhage Bleeding is a complication of OC that is typically related to polypectomy and is only rarely seen in the setting of a purely diagnostic examination. It has been reported in up to 1 to 2% of therapeutic cases.7,13,14 Although bleeding occurs at a much higher frequency than perforation, this complication is typically less severe, with most cases responding to supportive measures. Blood product transfusion as a corrective intervention is necessary in only a small minority of cases.
Curr Probl Diagn Radiol, July/August 2008
OC-related hemorrhage can be divided into two categories of immediate and delayed bleeding. Immediate bleeding concerns those that occur and are recognized at the time of the initial OC examination or in the immediate postprocedural time period. In most cases, the mechanism is believed to be related to inadequate electrocautery or incomplete shearing during polypectomy, leading to hemorrhage from the exposed tissue. Although there is not a consensus as to the exact definition of delayed bleeding, those that
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FIG 9. Intramural hematoma following polypectomy. (A and B) Digital scout radiograph (A) demonstrates attenuation of the air column and mass effect (asterisk) on the ascending colon. Transverse CT image (B) confirms the presence of a large intramural hematoma (arrow). (C) Small intramural hematoma (arrowhead) in a different patient that would likely not be seen at conventional radiography.
occur after the immediate procedural setting and within approximately 12 days are generally classified as delayed bleeds.15 The mechanism of delayed hemorrhage is not well understood but likely represents either a sloughing of the healed tissue plug or a
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subsequent progression of the initial injury into the deeper tissues. Of course, the risk of a bleeding complication increases significantly in the setting of anticoagulation, medications such as aspirin or Plavix, a bleeding diathesis, or problems in the coagulation
Curr Probl Diagn Radiol, July/August 2008
FIG 10. Intraluminal hemorrhage after therapeutic polyp removal. (A and B) Digital subtraction image during catheter angiography (A) demonstrates a rounded collection of contrast (arrow) in the descending colon consistent with active bleeding. Post pitressin (B) infusion demonstrates subsequent control of hemorrhage. (C and D) Endoscopic image (C) in a different patient demonstrates active bleeding following polypectomy. Subsequent image (D) depicts bleeding cessation following placement of hemostatic clips. (Color version of figure is available online.)
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cascade related to underlying conditions such as cirrhosis, malnutrition, renal failure, etc. Certain polyp characteristics that increase the risk of bleeding at OC polypectomy have also been identified. Polyp size is a major determinant, with lesions greater than 2 cm at increased risk as well as increasing diameter of the stalk for pedunculated polyps.16 There are several imaging manifestations of bleeding following OC. One common presentation is a localized intramural hematoma. Conventional radiographs are generally unremarkable in such cases, unless the hematoma is large enough to exert mass effect. CT can obviously demonstrate much smaller localized hematomas, which may appear high in attenuation on noncontrast imaging (Fig 9). A second common manifestation involves intraluminal bleeding, typically stemming from a polypectomy site. If this complication is detected at the time of OC, endoscopic measures to stop the bleeding can be employed including cautery, epinephrine injection, and placement of hemostatic clips. If the bleeding is more delayed, the patient will generally present with hematochezia. Imaging with radionuclide scintigraphy (technetium-labeled red blood cell scan) or angiography may be useful in diagnosis depending on the rate of bleed. The tagged red cell scan is sensitive for detecting ongoing bleeding, which manifests as a focus of radiotracer activity in the affected colon. CT angiography may offer similar diagnostic information more rapidly in the setting of suspected GI bleeding but further investigation for this indication is needed. Catheter-based angiography can detect active arterial bleeding and also allows for therapy in such cases (Fig 10). A third potential bleeding manifestation is intraperitoneal hemorrhage, which can be extensive given the large potential space of the peritoneal cavity. Similar to the trauma setting, CT is a very useful tool for the detection of peritoneal fluid in hemodynamically stable patients (Fig 11). In unstable patients, ultrasound can rapidly detect intraperitoneal fluid before surgery. Intraperitoneal blood can be seen remote from the bleeding site, with common locations including the paracolic gutters, dependent pelvis, and perihepatic space.
Postpolypectomy Syndromes A third major category of OC-related complications entails postpolypectomy syndromes. Subcategories include postpolypectomy distention syndrome and postpolypectomy coagulation syndrome. These are essen-
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FIG 11. Intraperitoneal hemorrhage following descending colonic polypectomy. (A) Transverse CT image demonstrates fluid about the liver and spleen (arrows) consistent with hemoperitoneum. (B) Lower image demonstrates a focal hematoma (asterisk) related to the descending colon following polypectomy and the source of the intraperitoneal hemorrhage.
tially diagnoses of exclusion where the potentially severe consequences of perforation and significant bleeding have been excluded. Postpolypectomy distention syndrome describes severe abdomen pain with a rigid abdomen secondary to marked overdistention of the air-filled colon.15 Suggestive imaging findings include massive gaseous dilation of the large bowel (and small bowel if the ileocecal valve is incompetent), but the appearance is nonspecific and only relative in nature since prominent distention is nearly universal. Conventional radiography (including left lateral decubitus or upright views)
Curr Probl Diagn Radiol, July/August 2008
is usually sufficient in this setting, but CT may be indicated to exclude other more ominous complications such as perforation and hemorrhage. Overdiagnosis is possible in patients with an underlying large-caliber but otherwise normal colon (Fig 12). Positioning the patient prone or decubitus with the left side up often relieves the situation of overdistention by allowing the trapped gas (often in the transverse colon) to move distally. Postpolypectomy coagulation syndrome, also referred to as serositis of transmural burn, occurs when the electrocautery injury during polypectomy is transmural with extension beyond the mucosa and submucosa.15 This complication represents the least severe end of the perforation spectrum, essentially a “mini-perforation.” Conventional radiography is unremarkable in this setting. CT may demonstrate minimal localized wall thickening and soft-tissue stranding of the pericolonic fat, without a frank perforation or large hematoma (Fig 13). The injury is self-limited and typically resolves within 48 hours with supportive measures only.
Sedation-Related Events The final major category involves issues related to sedation as a complication of OC. In general, there is no imaging manifestation for this category of complications, unless of a cardiopulmonary nature. In contrast to CT colonography, OC is typically performed with the patient under relatively heavy conscious sedation (Fig 14). According to one survey, oversedation with resulting cardiopulmonary depression occurred in 0.5% of cases.17 In particular, patients with chronic obstructive pulmonary disease and other chronic respiratory disorders may be at risk from oversedation. Of note, oversedation may blunt the patient’s ability to respond to pain due to overdistension or traction on the mesentery, which may in turn increase the risk for perforation and bleeding. On the other hand, undersedation may result in such pain and discomfort that the procedure cannot be completed.
Rare and Unusual Complications Infrequently, OC can result in unusual complications including pneumothorax, mesenteric tears, colonic volvulus, appendicitis, diverticulitis, and splenic trauma. Splenic injury may be caused by
Curr Probl Diagn Radiol, July/August 2008
FIG 12. Postpolypectomy distention syndrome mimic. (A and B) Abdominal radiograph (A) and coronal MPR (B) demonstrate a markedly distended air-filled colon. If symptomatic, the diagnosis of postpolypectomy distention syndrome would likely be applied after the exclusion of perforation or bleeding. In actuality, these images are post-CTC in an asymptomatic individual and represent a large-caliber normal colon.
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FIG 13. Postpolypectomy coagulation syndrome. (A and B) Large tubulovillous adenoma (A) removed by electrocautery polypectomy. CT (B) for post procedure pain demonstrates pericolonic inflammatory changes (arrow) consistent with postpolypectomy coagulation syndrome. Patient recovered with expectant management only. (Color version of figure is available online.)
either traction on the splenocolic ligament, traction on adhesions between the spleen and colon, or direct trauma from the endoscope (typically in setting of splenomegaly).18 At cross-sectional imaging, lacerations of the spleen depicted by stellate low-attenuation abnormalities through the parenchyma of the spleen and perisplenic hematoma can be demonstrated (Fig 15).
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FIG 14. A 75-year-old male oversedated for colonoscopy. (A and B) Subject hypotensive due to oversedation at colonoscopy. Examination thus incomplete. CTC done at a later date (A) demonstrates a villous adenoma in the ascending colon which was confirmed at repeat colonoscopy (B). (Color version of figure is available online.)
Conclusion Clinically relevant complications resulting from OC are relatively infrequent but may result in significant morbidity and even mortality. CT is a very effective tool for excluding colonic perforation, which often
Curr Probl Diagn Radiol, July/August 2008
FIG 15. Splenic injury following optical colonoscopy. Crescentic fluid collection (arrow) consistent with subcapsular splenic hematoma related to splenic trauma from colonoscopy several days prior.
manifests with extraluminal gas in a predominately extraperitoneal location. Conventional radiography is relatively insensitive for detection of such extraperitoneal gas. A variety of imaging modalities can play an important role in the setting of suspected bleeding complications, but conventional radiography is of little value. Exclusion of the feared complications of perforation and significant bleeding are important for appropriate clinical management of the patient.
REFERENCES 1. Kozarek RA, Earnest DL, Silverstein ME, et al. Air-pressureinduced colon injury during diagnostic colonoscopy. Gastroenterology 1980;78:7-14. 2. Han SY, Tishler JM. Perforation of the colon above the peritoneal reflection during the barium-enema examination. Radiology 1982;144:253-5. 3. Farley DR, Bannon MP, Zietlow SP, et al. Management of colonoscopic perforations. Mayo Clin Proc 1997;72:729-33.
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4. Anderson ML, Pasha TM, Leighton JA. Endoscopic perforation of the colon: Lessons from a 10-year study. Am J Gastroenterol 2000;95:3418-22. 5. Levin TR, Zhao W, Conell C, et al. Complications of colonoscopy in an integrated health care delivery system. Ann Intern Med 2006;145:880-6. 6. Korman LY, Overholt BF, Box T, et al. Perforation during colonoscopy in endoscopic ambulatory surgical centers. Gastrointest Endosc 2003;58:554-7. 7. Waye JD, Lewis BS, Yessayan S. Colonoscopy: A prospective report of complications. J Clin Gastroenterol 1992;15:347-51. 8. Gatto NM, Frucht H, Sundararajan V, et al. Risk of perforation after colonoscopy and sigmoidoscopy: A population-based study. J Natl Cancer Inst 2003;95:230-6. 9. Levine MS, Scheiner JD, Rubesin SE, et al. Diagnosis of pneumoperitoneum on supine abdominal radiographs. AJR 1991;156:731-5. 10. Hainaux B, Agneessens E, Bertinotti R, et al. Accuracy of MDCT in predicting site of gastrointestinal tract perforation. AJR 2006;187:1179-83. 11. Molmenti EP, Balfe DM, Kanterman RY, et al. Anatomy of the retroperitoneum: Observations of the distribution of pathologic fluid collections. Radiology 1996;200:95-103. 12. St. Peter SD, Abbas MA, Kelly KA. The spectrum of pneumatosis intestinalis. Arch Surg 2003;138:68-75. 13. Dafnis G, Ekborn A, Pahlman L, et al. Complications of diagnostic and therapeutic colonoscopy within a defined population in Sweden. Gastrointest Endosc 2001;54:302-9. 14. Silvis SE, Nebel O, Rogers G, et al. Endoscopic complications: Results of the 1974 American Society for Gastrointestinal Endoscopy survey. JAMA 1976;235:928-30. 15. Waye JD, Kahn O, Auerbach ME. Complications of colonoscopy and flexible sigmoidoscopy. Gastrointest Endosc Clin North Am 1996;6:343-77. 16. Macrae FA, Tan KG, Williams CB. Towards safer colonoscopy: A report on the complications of 5000 diagnostic or therapeutic colonoscopies. Gut 1983;24:376-83. 17. Keeffe E, O’Connor K. 1989 A/S/G/E survey of endoscopic sedation and monitoring practices. Gastrointest Endosc 1990; 36:S13-8. 18. Ahmed A, Eller PM, Schiffman FJ. Splenic rupture: An unusual complication of colonoscopy. Am J Gastroenterol 1997;92:1201-4.
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Optical colonoscopy (OC) is an essential component of colorectal cancer screening. In addition to favorable polyp detection capabilities, OC has a unique therapeutic role with the ability to remove identified polyps. However, this procedure carries a low but real risk for morbidity and mortality. OC requires physical intubation of the length of the colon and manipulation of the instrument. In addition, the performance of therapeutic polyp removal increases risk. Inherent to this procedure are several pathways for potential adverse events. Complications can be divided into several major categories including perforation, hemorrhage, postpolypectomy syndromes, and issues related to sedation. The imaging manifestations of complications related to optical colonoscopy as well as the potential underlying mechanisms will be reviewed. Emphasis will be placed on cross-sectional imaging given the improved sensitivity and specificity over conventional radiography.
Optical colonoscopy (OC) is a valuable tool in the detection of colorectal neoplasia and the prevention of cancer. Given its favorable performance characteristics for polyp detection and unique therapeutic ability, OC will undoubtedly remain an essential component of colorectal screening. However, this procedure carries a low but real risk for morbidity and mortality. OC requires physical intubation of the length of the colon and manipulation of the instrument. In addition, the performance of therapeutic polyp removal increases risk. Inherent to this procedure are several pathways for potential adverse events. Complications can be divided into several major categories including perfoFrom the aDepartment of Radiology, University of Wisconsin Medical School, Madison, WI; and bMallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO. Reprint requests: David H. Kim, MD, Department of Radiology, University of Wisconsin Medical School, E3/311 Clinical Science Center, 600 Highland Ave., Madison, WI 53792-3252. E-mail: [email protected]. Curr Probl Diagn Radiol 2008;37:165-77. © 2008 Mosby, Inc. All rights reserved. 0363-0188/2008/$34.00 ⫹ 0 doi:10.1067/j.cpradiol.2007.10.004
Curr Probl Diagn Radiol, July/August 2008
ration, hemorrhage, postpolypectomy syndromes, and issues related to sedation. This review demonstrates the radiologic imaging manifestations of various colonoscopic complications including some rare and unusual complications related to this procedure. Emphasis will be placed on computed tomographic (CT) evaluation given its increased sensitivity and increased characterization of suspected OC complications over conventional radiography.
Perforation Perforation may occur from one of two pathways in the absence of therapeutic procedures. One recognized mechanism involves pneumatic distension with barotrauma. Colonoscopy can generate wall pressures of up to 140 mm Hg, which has been shown to create colonic tears in animal and cadaveric studies.1 Typically, the tears involve the serosal layer along the longitudinal axis of the colon. This allows herniation and thinning of the mucosa through these tears, ultimately leading to a perforation. As predicted by LaPlace’s law where pressure is proportional to diameter, the capacious nature of the cecum is a frequent location from these types of tears.1 Such perforations can lead to massive amounts of free air.2 The second and perhaps more common manner of perforation is related to mechanical trauma from the endoscope either by direct injury from the end of the scope or by an abrasive injury from the side of the scope as it is pushed forward. Maneuvers such as straightening the sigmoid colon and the slide-by maneuver also increase the risk for perforation. These injuries typically occur in the sigmoid colon and left colon.3,4 At therapeutic colonoscopy, the performance of polyp removal adds another possible mechanism for perforation related to a through-and-through injury of the colonic wall. Polypectomies significantly increase risk for perfora-
165
FIG 1. A 66-year-old female undergoing screening colonoscopy complicated by sigmoid perforation. (A-C) Note the extraperitoneal location of air on these three transverse images despite rupture of an intraperitonealized colonic segment. Air has tracked back along the sigmoid mesentery and then dissects cephalad up the retroperitoneal fascia planes (arrows). (D) CT colonography performed 6 months later to complete screening demonstrates a 17-mm sigmoid polyp. Therapeutic OC with polypectomy revealed an advanced tubular adenoma. (Color version of figure is available online.)
tion in comparison to colonoscopic exams without polypectomy.5 The location of perforation is related to the location of the polypectomy as would be expected. Although the overall perforation rate at OC is relatively low, ranging widely from 0.3 to 3 cases per 1000 examinations,3,4,6-8 it is a serious complication that often requires surgical intervention. The radiologic imaging findings of colonic perforation resulting from OC are dependent on the location of injury. Perforations of intraperitoneal colonic seg-
166
ments on a mesentery including the transverse colon, sigmoid colon, and cecum will more often lead to free intraperitoneal air and fluid, whereas perforation of the ascending colon, descending colon, and rectum are more likely to result in extraperitoneal air and fluid. However, it is important to note that perforation of intraperitoneal colonic segments can often result in only extraperitoneal air when contained within its supplying mesentery (eg, the sigmoid mesocolon) (Fig 1).
Curr Probl Diagn Radiol, July/August 2008
FIG 2. Cecal perforation following OC. (A and B) Two transverse CT images demonstrate extravasation following perforation. There are small amounts of fluid adjacent to the right colon (arrow) as well as fairly large amounts of extravasated contrast layering dependently in the pelvis (arrowhead).
When the colon is perforated at an intraperitoneal portion, there is free leakage of air and often fluid into the peritoneal cavity. While upright or decubitus abdominal radiographs can detect small amounts of free intraperitoneal air, it is important to note that supine radiographs are fairly insensitive until relatively large amounts of intraperitoneal air are present, with demonstration of increased lucency over the liver and visualization of the serosal surface of the bowel wall (Rigler’s sign).9 In addition, conventional radiographs are insensitive to the presence of fluid. On the other
Curr Probl Diagn Radiol, July/August 2008
FIG 3. Extraperitoneal perforation following rectal polypectomy. (A) Abdominal radiograph is grossly negative following this subtle perforation. (B) Transverse CT image clearly demonstrates small amounts of extraluminal air (arrow), which remains in an extraperitoneal location as the perforation occurred below the peritoneal reflection. Note the value of CT and relative insensitive nature of radiographs for small extraperitoneal perforations.
hand, CT can readily detect small amounts of both free intraperitoneal air and fluid. When extraluminal fluid is present, it tends to collect in dependent portions such as the hepatorenal fossa (Morrison’s pouch), the paracolic gutters, the mesenteric root, and in the pelvis
167
(Fig 2). In some cases, there may be foci of extraluminal gas congregating near the perforation site, which may hint at its location.10 Air may also be seen locally tracking within the bowel wall (pneumatosis coli). When the perforation at OC primarily results in extraperitoneal gas without pneumoperitoneum, the radiographic presentation is markedly different. In this situation, extraluminal air dissects from the site of colonic perforation within the subperitoneal space contained by peritoneal ligaments and mesenteries, as well as tracking along extraperitoneal and retroperitoneal fascial planes.11 In our experience, this situation is more frequent than frank pneumoperitoneum. CT is much more effective in the diagnosis compared with conventional radiography, where detection of smaller amounts of extraperitoneal gas can be very difficult (Fig 3). As the amount of extraperitoneal air increases, these collections may coalesce into large pockets that exert mass effect on adjacent abdominal organs. Gas may eventually extend into the peritoneal cavity, resulting in secondary pneumoperitoneum (Fig 4). Subperitoneal gas may also track into the mediastinum and even result in subcutaneous emphysema in the neck and chest (Fig 5). Colonoscopy (with or without polypectomy) may also lead to dissection of air within the wall of the colon or pneumatosis. The exact mechanism is unknown but may be related to mucosal injury and increased intraluminal pressure.12 Pneumatosis coli typically presents as submucosal lucent collections within the wall at CT. Colonic pneumatosis can be fairly extensive and then be identified at conventional radiography. The air may dissect into the mesenteric venous system and into the portal veins. This can lead to foci of air trapped within the periphery of the liver within small portal venous branches (Fig 6). Colonic perforation at OC may present acutely with peritonitis or subacutely with abscess formation. Bacterial seeding of parenchymal organs is a consideration in this clinical situation when the patient demonstrates persistent fevers (Fig 7). When imaging is indicated, CT is clearly favored over conventional radiography. Although OC-related injuries occur in the setting of a “prepared” colon, the incidence of local and diffuse soiling is high. One study found local soiling in 48% of cases and diffuse feculent material in 21% of cases at exploratory laparotomy.3 Although nonsurgical management may be initially pursued in a small subset of patients who are hemodynamically stable with no
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FIG 4. Rectal perforation following OC. (A-C) Three selected transverse CT images demonstrate extraperitoneal perforation with subsequent extension into the peritoneal cavity. Note the free intraperitoneal air accumulating anterior to the liver (arrow).
Curr Probl Diagn Radiol, July/August 2008
FIG 5. An 81-year-old female who underwent diagnostic OC for melana. Ninety minutes after the procedure, she experienced abdominal pain and facial crepitus. (A and B) Transverse CT images demonstrate extensive retroperitoneal air, which extends up the chest to the neck, related to this colonic perforation. (C) Digital scout nicely depicts the extensive subcutaneous extension of air.
FIG 6. Pneumatosis coli and portal venous gas following colonoscopy. (A and B) Transverse CT image (A) demonstrates multiple lucencies in the colonic wall in the right colon consistent with pneumatosis (arrow). CT image (B) through the liver demonstrates scattered portal venous gas trapped in tiny peripheral venous branches (arrowheads).
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FIG 7. Subacute sequelae from colonic perforation. (A-C) CT images (A and B) demonstrate a pericolonic abscess (arrows) noted several days after screening OC. Patient presented with shaking fever and chills. Contrast injection (C) of subsequently placed abscess drain demonstrates the amorphous abscess cavity. The patient ultimately underwent a right hemicolectomy. (D) CT image of a different patient demonstrates a hepatic abscess (arrowhead) in a patient several days following screening OC with hepatic flexure polypectomy.
signs of peritonitis, prompt surgical treatment is favored in the majority of cases to decrease overall morbidity. In some cases with subacute presentation, image-guided abscess drainage may be indicated before definitive surgical intervention. In cases where colorectal evaluation at OC is incomplete due to perforation (or any other cause
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for that matter), it is important to eventually complete the evaluation after the complication is resolved. CT colonography (also referred to as virtual colonoscopy) represents an excellent minimally invasive means for evaluating the proximal colon in cases where the endoscope at OC fails to reach the cecum (Fig 8).
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FIG 8. Incomplete screening OC in a 74-year-old female. (A) Abdominal radiograph with massive free air from an incomplete screening colonoscopy to the sigmoid colon complicated by perforation. Surgical repair (segmental sigmoid resection with primary anastomosis) was required. (B-D) Transverse 2D (B) and 3D (C) images demonstrate one of two unsuspected annular carcinomas (arrows) identified at CT colonography performed 16 months later to complete screening. OC image (D) confirms the mass. (Color version of figure is available online.)
Hemorrhage Bleeding is a complication of OC that is typically related to polypectomy and is only rarely seen in the setting of a purely diagnostic examination. It has been reported in up to 1 to 2% of therapeutic cases.7,13,14 Although bleeding occurs at a much higher frequency than perforation, this complication is typically less severe, with most cases responding to supportive measures. Blood product transfusion as a corrective intervention is necessary in only a small minority of cases.
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OC-related hemorrhage can be divided into two categories of immediate and delayed bleeding. Immediate bleeding concerns those that occur and are recognized at the time of the initial OC examination or in the immediate postprocedural time period. In most cases, the mechanism is believed to be related to inadequate electrocautery or incomplete shearing during polypectomy, leading to hemorrhage from the exposed tissue. Although there is not a consensus as to the exact definition of delayed bleeding, those that
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FIG 9. Intramural hematoma following polypectomy. (A and B) Digital scout radiograph (A) demonstrates attenuation of the air column and mass effect (asterisk) on the ascending colon. Transverse CT image (B) confirms the presence of a large intramural hematoma (arrow). (C) Small intramural hematoma (arrowhead) in a different patient that would likely not be seen at conventional radiography.
occur after the immediate procedural setting and within approximately 12 days are generally classified as delayed bleeds.15 The mechanism of delayed hemorrhage is not well understood but likely represents either a sloughing of the healed tissue plug or a
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subsequent progression of the initial injury into the deeper tissues. Of course, the risk of a bleeding complication increases significantly in the setting of anticoagulation, medications such as aspirin or Plavix, a bleeding diathesis, or problems in the coagulation
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FIG 10. Intraluminal hemorrhage after therapeutic polyp removal. (A and B) Digital subtraction image during catheter angiography (A) demonstrates a rounded collection of contrast (arrow) in the descending colon consistent with active bleeding. Post pitressin (B) infusion demonstrates subsequent control of hemorrhage. (C and D) Endoscopic image (C) in a different patient demonstrates active bleeding following polypectomy. Subsequent image (D) depicts bleeding cessation following placement of hemostatic clips. (Color version of figure is available online.)
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cascade related to underlying conditions such as cirrhosis, malnutrition, renal failure, etc. Certain polyp characteristics that increase the risk of bleeding at OC polypectomy have also been identified. Polyp size is a major determinant, with lesions greater than 2 cm at increased risk as well as increasing diameter of the stalk for pedunculated polyps.16 There are several imaging manifestations of bleeding following OC. One common presentation is a localized intramural hematoma. Conventional radiographs are generally unremarkable in such cases, unless the hematoma is large enough to exert mass effect. CT can obviously demonstrate much smaller localized hematomas, which may appear high in attenuation on noncontrast imaging (Fig 9). A second common manifestation involves intraluminal bleeding, typically stemming from a polypectomy site. If this complication is detected at the time of OC, endoscopic measures to stop the bleeding can be employed including cautery, epinephrine injection, and placement of hemostatic clips. If the bleeding is more delayed, the patient will generally present with hematochezia. Imaging with radionuclide scintigraphy (technetium-labeled red blood cell scan) or angiography may be useful in diagnosis depending on the rate of bleed. The tagged red cell scan is sensitive for detecting ongoing bleeding, which manifests as a focus of radiotracer activity in the affected colon. CT angiography may offer similar diagnostic information more rapidly in the setting of suspected GI bleeding but further investigation for this indication is needed. Catheter-based angiography can detect active arterial bleeding and also allows for therapy in such cases (Fig 10). A third potential bleeding manifestation is intraperitoneal hemorrhage, which can be extensive given the large potential space of the peritoneal cavity. Similar to the trauma setting, CT is a very useful tool for the detection of peritoneal fluid in hemodynamically stable patients (Fig 11). In unstable patients, ultrasound can rapidly detect intraperitoneal fluid before surgery. Intraperitoneal blood can be seen remote from the bleeding site, with common locations including the paracolic gutters, dependent pelvis, and perihepatic space.
Postpolypectomy Syndromes A third major category of OC-related complications entails postpolypectomy syndromes. Subcategories include postpolypectomy distention syndrome and postpolypectomy coagulation syndrome. These are essen-
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FIG 11. Intraperitoneal hemorrhage following descending colonic polypectomy. (A) Transverse CT image demonstrates fluid about the liver and spleen (arrows) consistent with hemoperitoneum. (B) Lower image demonstrates a focal hematoma (asterisk) related to the descending colon following polypectomy and the source of the intraperitoneal hemorrhage.
tially diagnoses of exclusion where the potentially severe consequences of perforation and significant bleeding have been excluded. Postpolypectomy distention syndrome describes severe abdomen pain with a rigid abdomen secondary to marked overdistention of the air-filled colon.15 Suggestive imaging findings include massive gaseous dilation of the large bowel (and small bowel if the ileocecal valve is incompetent), but the appearance is nonspecific and only relative in nature since prominent distention is nearly universal. Conventional radiography (including left lateral decubitus or upright views)
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is usually sufficient in this setting, but CT may be indicated to exclude other more ominous complications such as perforation and hemorrhage. Overdiagnosis is possible in patients with an underlying large-caliber but otherwise normal colon (Fig 12). Positioning the patient prone or decubitus with the left side up often relieves the situation of overdistention by allowing the trapped gas (often in the transverse colon) to move distally. Postpolypectomy coagulation syndrome, also referred to as serositis of transmural burn, occurs when the electrocautery injury during polypectomy is transmural with extension beyond the mucosa and submucosa.15 This complication represents the least severe end of the perforation spectrum, essentially a “mini-perforation.” Conventional radiography is unremarkable in this setting. CT may demonstrate minimal localized wall thickening and soft-tissue stranding of the pericolonic fat, without a frank perforation or large hematoma (Fig 13). The injury is self-limited and typically resolves within 48 hours with supportive measures only.
Sedation-Related Events The final major category involves issues related to sedation as a complication of OC. In general, there is no imaging manifestation for this category of complications, unless of a cardiopulmonary nature. In contrast to CT colonography, OC is typically performed with the patient under relatively heavy conscious sedation (Fig 14). According to one survey, oversedation with resulting cardiopulmonary depression occurred in 0.5% of cases.17 In particular, patients with chronic obstructive pulmonary disease and other chronic respiratory disorders may be at risk from oversedation. Of note, oversedation may blunt the patient’s ability to respond to pain due to overdistension or traction on the mesentery, which may in turn increase the risk for perforation and bleeding. On the other hand, undersedation may result in such pain and discomfort that the procedure cannot be completed.
Rare and Unusual Complications Infrequently, OC can result in unusual complications including pneumothorax, mesenteric tears, colonic volvulus, appendicitis, diverticulitis, and splenic trauma. Splenic injury may be caused by
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FIG 12. Postpolypectomy distention syndrome mimic. (A and B) Abdominal radiograph (A) and coronal MPR (B) demonstrate a markedly distended air-filled colon. If symptomatic, the diagnosis of postpolypectomy distention syndrome would likely be applied after the exclusion of perforation or bleeding. In actuality, these images are post-CTC in an asymptomatic individual and represent a large-caliber normal colon.
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FIG 13. Postpolypectomy coagulation syndrome. (A and B) Large tubulovillous adenoma (A) removed by electrocautery polypectomy. CT (B) for post procedure pain demonstrates pericolonic inflammatory changes (arrow) consistent with postpolypectomy coagulation syndrome. Patient recovered with expectant management only. (Color version of figure is available online.)
either traction on the splenocolic ligament, traction on adhesions between the spleen and colon, or direct trauma from the endoscope (typically in setting of splenomegaly).18 At cross-sectional imaging, lacerations of the spleen depicted by stellate low-attenuation abnormalities through the parenchyma of the spleen and perisplenic hematoma can be demonstrated (Fig 15).
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FIG 14. A 75-year-old male oversedated for colonoscopy. (A and B) Subject hypotensive due to oversedation at colonoscopy. Examination thus incomplete. CTC done at a later date (A) demonstrates a villous adenoma in the ascending colon which was confirmed at repeat colonoscopy (B). (Color version of figure is available online.)
Conclusion Clinically relevant complications resulting from OC are relatively infrequent but may result in significant morbidity and even mortality. CT is a very effective tool for excluding colonic perforation, which often
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FIG 15. Splenic injury following optical colonoscopy. Crescentic fluid collection (arrow) consistent with subcapsular splenic hematoma related to splenic trauma from colonoscopy several days prior.
manifests with extraluminal gas in a predominately extraperitoneal location. Conventional radiography is relatively insensitive for detection of such extraperitoneal gas. A variety of imaging modalities can play an important role in the setting of suspected bleeding complications, but conventional radiography is of little value. Exclusion of the feared complications of perforation and significant bleeding are important for appropriate clinical management of the patient.
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