Patients with inflammatory bowel disease who experience abdominal pain and gastrointestinal symptoms often seek care in the emergency department (ED). These patients commonly undergo abdominopelvic computed tomography (CT) as part of their evaluation, and the rate of imaging appears to be increasing without a corresponding increase in identification of clinically actionable findings or effect on disposition. Studies demonstrate that the yield of CT tends to be fairly high. Yet, because inflammatory bowel disease is often diagnosed at an early age, these patients are repeatedly imaged during their lifetime, a subset of whom accumulate high levels of ionizing radiation exposure, increasing their risk of cancer. This compounds an already increased risk of cancer in these patients because of inflammatory bowel disease alone. Lack of intimate knowledge of a patient’s disease phenotype and disease progression contributes to uncertainty in distinguishing between an inflammatory exacerbation; a complication such as obstruction, abscess, perforation, fistula, or stricture; and a noninflammatory-bowel-disease-related condition. This uncertainty can lead to overuse of imaging with CT. Limited availability of and lack of awareness of alternate imaging modalities and strategies may prevent providers from pursuing strategies that avoid ionizing radiation. In this article, we review options for imaging inflammatory bowel disease patients in the ED and attempts undertaken to risk stratify these patients, and we discuss ways in which details of a patient’s disease might guide imaging decisionmaking.
Introduction
Crohn’s disease and ulcerative colitis, collectively termed inflammatory bowel disease , are chronic remitting and relapsing diseases of the gastrointestinal tract that affect 1.4 million US citizens and nearly 4 million people worldwide.
Ulcerative colitis is characterized by diffuse mucosal inflammation limited to the colon. It involves the rectum in nearly all cases and may extend proximally in a symmetrical, circumferential, and uninterrupted pattern to involve the mucosa and submucosa of part or all of the colon. Crohn’s disease is a collection of inflammatory diseases arising from complex interactions of host susceptibility genes, host microbiome, and the environment. It is transmural and can involve any part of the gastrointestinal tract from the mouth to the anus. Although inflammation is the hallmark of Crohn’s disease, complications of poorly controlled disease result in strictures, fistulae, obstruction, and perforation. Symptoms of exacerbations include acute or acute-on-chronic abdominal pain, fever, diarrhea, bloody stools, and weight loss. The prevalence of inflammatory bowel disease has steadily increased during the past 2 decades, particularly among minorities, with direct medical costs estimated at $18,000 to $19,000 per patient per year. Emergency department (ED) evaluations for exacerbations of inflammatory bowel disease increased nearly 3-fold in the United States between 1994 and 2005. This has occurred in the context of increases in ED utilization of nearly 30% during this timeframe, whereby the ED now accounts for approximately a third of all acute care visits in the United States. Accordingly, increases in ED visits for inflammatory bowel disease patients likely reflect in part these overall trends.
Critical decision points in the ED evaluation include whether to attribute a patient’s symptoms to an exacerbation of inflammatory bowel disease, an associated complication, an infection such as Clostridium difficile , or an unrelated clinical entity (eg, appendicitis). Providers must determine whether in addition to the patient’s history, physical examination findings, and laboratory test results, imaging is needed to exclude serious pathology. This can be particularly challenging if the patient’s disease phenotype is not known or established.
Phenotype is the term used primarily in Crohn’s disease to describe a patient’s disease pattern, which is characterized primarily by age at diagnosis, predominant disease location, and behavior. Classification schemes define location as small bowel, large bowel, or perianal intestine and disease behavior pattern as penetrating (fistula or abscess), fibrostenotic, or inflammatory (limited to the intestinal mucosa and submucosa). Although disease phenotype (particularly location) is relatively stable in the short term, Crohn’s disease tends to develop into stricturing or penetrating disease within 5 to 20 years, requiring surgical intervention in up to two thirds of patients. Gastroenterologists rely on phenotypic classification for various aspects of clinical decisionmaking and for predicting a patient’s clinical course. For example, information on disease location is used to identify patients who might benefit from topical therapy, and information on disease behavior and progression (mild or aggressive) guides decisions about suitability for immunosuppressive therapy.
Imaging and Associated Radiation Exposure among Patients with Inflammatory Bowel Disease
Imaging plays a central role in the diagnosis of inflammatory bowel disease, assessment of disease activity, evaluation of complications, and monitoring of response to therapy. In part because inflammatory bowel disease is usually diagnosed during early adulthood, with up to 20% of patients receiving a diagnosis during childhood, these patients often undergo numerous imaging studies over a lifetime, exposing them to ionizing radiation. This includes radiography, fluoroscopy, and especially computed tomography (CT). A typical abdominopelvic CT imparts approximately 10 mSv of radiation. Multiple studies have reported elevated levels of radiation exposure among patients with inflammatory bowel disease, including subsets of up to 21% with cumulative-effective doses in excess of 75 mSv. A recent study following 451 patients over 11 years found that by a median age of 40 years, 16% were exposed to a high radiation levels (a cumulative effective dose >50 mSv) and that 4% had a cumulative effective dose greater than 100 mSv. Although controversial, the widely used linear-no-threshold unadjusted risk model adopted by the Biologic Effects of Ionizing Radiation VII Conference holds that a 10-mSv exposure increases one’s lifetime attributable risk of cancer by 1/1,000 above baseline. Patients whose conditions lead to multiple or repeated imaging and those at inherently increased risk because of age or physiology (eg, women, children) are at greatest risk. Inflammatory bowel disease and use of immunomodulators to treat inflammatory bowel disease are associated with an increased baseline risk of luminal cancers and lymphoma. Repeated and multiple CT imaging, especially in children, compounds these risks.
Despite recent improvements in CT use overall, rates of CT use in the ED have continued to increase, a trend that some data suggest may also be the case for abdominopelvic CT in inflammatory bowel disease. These increases are likely due to many factors, including expectations of referring physicians for imaging in the ED. For patients who might be suitable for symptomatic treatment and discharge, absence of worrisome findings on ED imaging can provide clinicians and patients with confidence in a safe and prudent disposition. However, Kerner et al found that during an 8-year period, CT use in ED patients with Crohn’s disease increased from 47% to 78% of encounters, with no change in admission rate (68% in 2001 versus 71% in 2009) and no change in yield of CT. And yet, data also suggest that the yield of CT in identifying obstruction, perforation, abscess, or other urgent noninflammatory-bowel-disease-related diagnoses is fairly high, ranging from 32.1% to 38.7% in ED-based studies. In a Canadian study of 152 patients with Crohn’s disease and 130 with ulcerative colitis presenting to an ED over a 2-year period, CT was performed for 49% of the Crohn’s disease patients and 19% of the ulcerative colitis patients and was believed to change clinical management in 80% and 69% of encounters, respectively. This was based on incompletely specified criteria but included disease requiring drainage, surgery, or other intervention. However, nearly 30% of patients with Crohn’s disease and 16% of those with ulcerative colitis had more than 1 CT from the ED during the study period. Taken together, these data suggest that there is often benefit to this imaging but that there is also room for improvement. Researchers, clinicians, professional societies, and regulators have called for improvement efforts. These might include risk stratification, use of alternative imaging modalities (eg, ultrasonography, magnetic resonance imaging [MRI], magnetic resonance enterography), low-dose protocols, or nonimaging approaches (eg, admission and endoscopy).
What Modalities are Most Appropriate for Imaging Inflammatory Bowel Disease in the ED?
The choice of modality for imaging in inflammatory bowel disease should be informed by the clinical presentation informed by the patient’s disease phenotype, if known, and weighed against the potential harms of ionizing radiation in this generally young patient population. The American College of Radiology’s evidence-based recommendations on imaging strategies for Crohn’s disease rate the appropriateness of each modality for different clinical scenarios. Although these were not created specifically for the ED setting, the most relevant scenarios include (1) an adult with known Crohn’s disease presenting with acute exacerbation and (2) an adult presenting with acute severe abdominal symptoms and suspected Crohn’s disease. In the first scenario, magnetic resonance enterography, CT enterography (CTE), and traditional CT with contrast are all rated as “usually appropriate,” with magnetic resonance enterography receiving the highest appropriateness score. In the second case, CT with contrast ranks as most appropriate because of its accessibility and fast acquisition for patients in severe distress. The following sections provide an overview of the different imaging modalities most relevant to the ED and their relative merits. Table 1 provides a summary of imaging and nonimaging modalities.
| Imaging Modality | Benefits | Disadvantages | Specific Indications | Protocol Details |
|---|---|---|---|---|
| CT of the abdomen/pelvis | Fast Reproducible Accessible | Ionizing radiation exposure Nephrotoxic contrast | Acute abdomen Suspected complication (eg, abscess, obstruction) | CT with intravenous contrast Oral contrast not essential |
| CTE | Good diagnostic performance | Ionizing radiation exposure Nephrotoxic contrast Oral contrast volume | Stable patient with known diagnosis | CT with oral and intravenous contrast |
| MRE | Good diagnostic performance No ionizing radiation | Not widely available Requires oral contrast | Stable patient with known diagnosis | MRI with oral and intravenous contrast Antiperistaltic agent used |
| MRI pelvis | Good soft tissue contrast resolution | Not widely available | Stable patient with known perianal fistulizing disease | High-resolution images of the pelvis with contrast |
| Ultrasonography | No ionizing radiation Inexpensive | Operator dependent | Evaluation of perianal abscess Intervention needed | Grayscale ultrasonography from transperineal approach |
| Admission and endoscopy | No ionizing radiation Accessible | Requires coordination with willing GI consultant | Stable patient for whom imaging can be delayed Evaluation of rectal/distal disease |
Imaging and Associated Radiation Exposure among Patients with Inflammatory Bowel Disease
Imaging plays a central role in the diagnosis of inflammatory bowel disease, assessment of disease activity, evaluation of complications, and monitoring of response to therapy. In part because inflammatory bowel disease is usually diagnosed during early adulthood, with up to 20% of patients receiving a diagnosis during childhood, these patients often undergo numerous imaging studies over a lifetime, exposing them to ionizing radiation. This includes radiography, fluoroscopy, and especially computed tomography (CT). A typical abdominopelvic CT imparts approximately 10 mSv of radiation. Multiple studies have reported elevated levels of radiation exposure among patients with inflammatory bowel disease, including subsets of up to 21% with cumulative-effective doses in excess of 75 mSv. A recent study following 451 patients over 11 years found that by a median age of 40 years, 16% were exposed to a high radiation levels (a cumulative effective dose >50 mSv) and that 4% had a cumulative effective dose greater than 100 mSv. Although controversial, the widely used linear-no-threshold unadjusted risk model adopted by the Biologic Effects of Ionizing Radiation VII Conference holds that a 10-mSv exposure increases one’s lifetime attributable risk of cancer by 1/1,000 above baseline. Patients whose conditions lead to multiple or repeated imaging and those at inherently increased risk because of age or physiology (eg, women, children) are at greatest risk. Inflammatory bowel disease and use of immunomodulators to treat inflammatory bowel disease are associated with an increased baseline risk of luminal cancers and lymphoma. Repeated and multiple CT imaging, especially in children, compounds these risks.
Despite recent improvements in CT use overall, rates of CT use in the ED have continued to increase, a trend that some data suggest may also be the case for abdominopelvic CT in inflammatory bowel disease. These increases are likely due to many factors, including expectations of referring physicians for imaging in the ED. For patients who might be suitable for symptomatic treatment and discharge, absence of worrisome findings on ED imaging can provide clinicians and patients with confidence in a safe and prudent disposition. However, Kerner et al found that during an 8-year period, CT use in ED patients with Crohn’s disease increased from 47% to 78% of encounters, with no change in admission rate (68% in 2001 versus 71% in 2009) and no change in yield of CT. And yet, data also suggest that the yield of CT in identifying obstruction, perforation, abscess, or other urgent noninflammatory-bowel-disease-related diagnoses is fairly high, ranging from 32.1% to 38.7% in ED-based studies. In a Canadian study of 152 patients with Crohn’s disease and 130 with ulcerative colitis presenting to an ED over a 2-year period, CT was performed for 49% of the Crohn’s disease patients and 19% of the ulcerative colitis patients and was believed to change clinical management in 80% and 69% of encounters, respectively. This was based on incompletely specified criteria but included disease requiring drainage, surgery, or other intervention. However, nearly 30% of patients with Crohn’s disease and 16% of those with ulcerative colitis had more than 1 CT from the ED during the study period. Taken together, these data suggest that there is often benefit to this imaging but that there is also room for improvement. Researchers, clinicians, professional societies, and regulators have called for improvement efforts. These might include risk stratification, use of alternative imaging modalities (eg, ultrasonography, magnetic resonance imaging [MRI], magnetic resonance enterography), low-dose protocols, or nonimaging approaches (eg, admission and endoscopy).
What Modalities are Most Appropriate for Imaging Inflammatory Bowel Disease in the ED?
The choice of modality for imaging in inflammatory bowel disease should be informed by the clinical presentation informed by the patient’s disease phenotype, if known, and weighed against the potential harms of ionizing radiation in this generally young patient population. The American College of Radiology’s evidence-based recommendations on imaging strategies for Crohn’s disease rate the appropriateness of each modality for different clinical scenarios. Although these were not created specifically for the ED setting, the most relevant scenarios include (1) an adult with known Crohn’s disease presenting with acute exacerbation and (2) an adult presenting with acute severe abdominal symptoms and suspected Crohn’s disease. In the first scenario, magnetic resonance enterography, CT enterography (CTE), and traditional CT with contrast are all rated as “usually appropriate,” with magnetic resonance enterography receiving the highest appropriateness score. In the second case, CT with contrast ranks as most appropriate because of its accessibility and fast acquisition for patients in severe distress. The following sections provide an overview of the different imaging modalities most relevant to the ED and their relative merits. Table 1 provides a summary of imaging and nonimaging modalities.
| Imaging Modality | Benefits | Disadvantages | Specific Indications | Protocol Details |
|---|---|---|---|---|
| CT of the abdomen/pelvis | Fast Reproducible Accessible | Ionizing radiation exposure Nephrotoxic contrast | Acute abdomen Suspected complication (eg, abscess, obstruction) | CT with intravenous contrast Oral contrast not essential |
| CTE | Good diagnostic performance | Ionizing radiation exposure Nephrotoxic contrast Oral contrast volume | Stable patient with known diagnosis | CT with oral and intravenous contrast |
| MRE | Good diagnostic performance No ionizing radiation | Not widely available Requires oral contrast | Stable patient with known diagnosis | MRI with oral and intravenous contrast Antiperistaltic agent used |
| MRI pelvis | Good soft tissue contrast resolution | Not widely available | Stable patient with known perianal fistulizing disease | High-resolution images of the pelvis with contrast |
| Ultrasonography | No ionizing radiation Inexpensive | Operator dependent | Evaluation of perianal abscess Intervention needed | Grayscale ultrasonography from transperineal approach |
| Admission and endoscopy | No ionizing radiation Accessible | Requires coordination with willing GI consultant | Stable patient for whom imaging can be delayed Evaluation of rectal/distal disease |
CT
CT is the workhorse imaging modality in the ED. With new-generation scanners, CTs can be performed in a matter of seconds, yielding reliable, high-resolution images. Abdominopelvic CT is the first-line modality in evaluating for obstruction, perforation, abscess, or other urgent noninflammatory-bowel-disease-related diagnoses. The drawbacks to CT imaging include radiation dose and the need for intravenous contrast for improved images, which adds the risk of kidney injury in patients with impaired renal function. Multidetector CT scanners provide even greater spatial resolution, with decreased radiation dose, although these can still impart significant lifetime cumulative exposures to patients undergoing repeated imaging. Many different CT protocols can be used to image patients with Crohn’s disease. Traditional or standard CT scans with intravenous contrast are acquired during the portal venous phase and provide good depiction of organ, bowel, and vascular enhancement. Though controversial, many centers have moved away from administration of oral contrast for routine abdominopelvic CT examinations. The advantage of oral contrast is to help delineate bowel loops from one another and from surrounding structures (lymph nodes, vessels, etc) because it is bright and improves soft tissue resolution between structures that otherwise are similar in attenuation to one another. The disadvantages of oral contrast include delays in diagnosis or surgical intervention and ED throughput, potentially increased radiation exposure because of dose modulation techniques currently used with many scanners and questionable added diagnostic benefit. Additionally, positive (bright) oral contrast may mask mucosal abnormalities associated with Crohn’s disease. Hence, a CT with intravenous contrast but without oral contrast has become the standard in many institutions ( Figures 1 and 2 ).
CTE
CTE is a specialized CT protocol designed to assess bowel disease, focusing on mural abnormalities and disease activity. It requires the patient to drink a large volume (1 to 1.5 L) of neutral or hyperosmotic oral contrast to achieve optimal bowel distention. CTE uses negative oral contrast (dark), rather than the oral contrast (bright) that may be used with traditional CT. The slice thickness and phases of intravenous contrast acquired in CTE are also optimized to provide more information about bowel pathology than traditional CT. Although CTE performs well for diagnosing and monitoring disease activity in Crohn’s disease patients, they may not tolerate the large volume of contrast this requires. When urgent symptoms are present or when there is suspected bowel obstruction, a traditional CT of the abdomen and pelvis with intravenous contrast is a better option. For patients with less urgent symptoms, providers should consider magnetic resonance enterography, discussed in detail below, because it provides similar diagnostic capability without ionizing radiation exposure. CT enteroclysis is another specialized protocol to evaluate the small bowel and differs from CTE in that it requires placement of a nasojejunal tube through which contrast is delivered. Because of the invasive nature of enteroclysis and lack of significant clinical benefit over enterography, most institutions no longer perform it.
Ultrasonography
Ultrasonography is increasingly accessible, is usually well tolerated by the patient, and avoids ionizing radiation and contrast administration. Several studies demonstrate the value of graded compression ultrasonography in detecting and diagnosing small bowel involvement and potential utility in detecting small bowel obstruction. However, ultrasonography is heavily operator dependent and may not be available during off hours. It is less reliable than CT or MRI in detecting complications of Crohn’s disease for disease more proximal than the ileocecal junction and has a more limited scope in identifying alternative diagnoses. Ultrasonography may not perform well in patients with large abdominal girth and gas within the lumen of distended bowel, as may be observed in the setting of obstruction. Guarding and severe pain can limit the ability to achieve adequate compression. Although some reports have suggested ultrasonography can be of benefit to diagnosing and monitoring Crohn’s disease in children, as is the case with adults, these results are highly dependent on the expertise and experience of the sonographer. Given these limitations, ultrasonography is generally not considered a first-line imaging test in adults with Crohn’s disease presenting to the ED. However, beyond small bowel assessment, it may be the modality of choice in patients with perianal fistulizing disease ( Figure 3 ). Rectal or vaginal ultrasonography can identify abscesses and also guide intervention (abscess drainage) without the need for an MRI scan. Ultrasonography does not impart ionizing radiation, is inexpensive, and is usually well tolerated by these patients.
MRI
Unlike CT, MRI tends to be a specialized examination that is protocolized according to the study indication to answer specific questions. For instance, in a patient with perianal fistulizing disease, a pelvic MRI with high-resolution imaging would be performed. The inherent soft tissue contrast achieved with MRI allows delineation of fistulous tracts relative to the sphincter complex, which may help guide therapeutic decisionmaking. This level of detail makes MRI a first-line imaging modality for perianal fistulizing disease in the nontoxic patient ( Figure 4 ). Limitations of MRI availability and potential acute need to treat or triage patients may make examination under anesthesia or ultrasonography a better option for ruling out an acute abscess in these patients.
Magnetic Resonance Enterography
Magnetic resonance enterography is an MRI examination with special sequences designed to capture bowel wall findings, particularly in the small bowel or terminal ileum. It has become a mainstay of surveillance imaging in Crohn’s disease patients because of performance similar to that of CTE and the lack of ionizing radiation ( Figures 5 and 6 ). In a study comparing preoperative magnetic resonance enterography with intraoperative findings in 35 patients, magnetic resonance enterography correctly identified bowel stenosis, with a sensitivity of 0.95 (95% confidence interval [CI] 0.76 to 0.99) and specificity of 0.72 (95% CI 0.39 to 0.92), and detected abscesses with a sensitivity of 0.92 (95% CI 0.62 to 0.99) and specificity of 0.90 (95% CI 0.69 to 0.98). Like CTE, magnetic resonance enterography requires a large volume of oral contrast. It also requires injection of an antiperistaltic agent to prevent image degradation from bowel motility. Unlike CT contrast, MRI contrast is not nephrotoxic at administered doses and can be given to properly screened patients with impaired renal function. Although ideal in the outpatient setting, magnetic resonance enterography may not always be accessible in the ED and entails higher cost. However, when available, it is an excellent option for patients who are nontoxic and for whom imaging can be delayed a few hours or until after admission. As is the case with CT enteroclysis, magnetic resonance enteroclysis requires placement of a nasojejunal tube to deliver contrast and has for the most part been abandoned as a routine imaging study, certainly for the ED.
