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Crohn Disease and Its Surgical Management
Crohn disease is an incurable, chronic disease of unknown etiology, which along with ulcerative colitis comprises inflammatory bowel disease (IBD). Crohn disease is characterized by transmural inflammation that can involve any part of the gastrointestinal tract, from mouth to anus, and presentations of the disease vary widely. Although there is no cure for Crohn disease at this time, great advances in medicine and surgery have aided in reducing the symptoms and suffering of these patients. As such, a multidisciplinary team approach to care, including specialized experts in gastroenterology, surgery, and radiology is essential to ensure these patients receive current, appropriate, and high-quality care.
Epidemiology
The exact number of Crohn disease cases is not known due to variability in reporting and diagnostic criteria. The estimated incidence in North America is 3.1 to 20.2 cases per 100,000 person-years. Current estimates of Crohn disease in a large cohort study of 9 million health insurance claims estimate prevalence to be 201 cases per 100,000 people. The prevalence of Crohn disease appears to be increasing despite steady annual incidence rates ; this could be due to improved survival from advances in medical and surgical therapies.
Risk Factors
Although the etiology of Crohn disease is unclear, the most common explanation is that a genetically predisposed individual comes into contact with an environmental trigger. Several important risk factors should be considered when a patient presents with an illness that could be Crohn disease. There is an overall female predominance in Crohn disease; however, there is no current evidence that there is a hormonal effect on disease expression. In addition, there is a bimodal distribution to the age at diagnosis with the highest peak between the second or third decade of life and a second peak in the sixth or seventh decade. Researchers have proposed that this bimodal distribution might be due to environmental factors, differences in disease presentation over time, or a delay in diagnosis until a relapse of the disease occurs. There is also a predominance of Crohn disease among certain ethnic and racial groups, with the highest incidence in Jewish and white populations compared with non-Jewish and black or Hispanic populations. These differences between racial and ethnic groups could be due to genetic or environmental factors.
Environmental Factors
The microbial environment of the gastrointestinal tract, including commensal and pathologic organisms, is important to maintaining intestinal health. An imbalance in this system is thought to play a role in the pathophysiology of Crohn disease. Therefore medications (including antibiotics, nonsteroidal antiinflammatory drugs, and oral contraceptive pills) and diet are thought to impact the development of Crohn disease. Specifically, a Western style diet including processed, fried, low-fiber, and sugary foods has been implicated in the development of Crohn disease. Previous studies suggest that improved hygiene is also associated with Crohn disease. Smoking is associated with an increased risk of Crohn disease and increased risk of disease recurrence and has been suggested to contribute to disease severity.
Genetic Factors
Breakthroughs in the field of genetics have aided in our understanding of Crohn disease. Although only 15% of patients with Crohn disease have a family history of IBD, patients with a first-degree relative with IBD are 3 to 20 times more likely to develop the disease compared with the general population. IBD appears to follow a nonmendelian pattern of inheritance. Monozygotic twins have a higher rate of disease (44%) than dizygotic twins (3.8%). This less than complete penetrance leads researchers to believe that environmental factors play a key role in disease development. In addition to the overall risk of developing Crohn disease within families, there appears to be concordance in the location (e.g., colonic vs. ileal) and phenotype (e.g., fistulizing vs. fibrostenotic) of the disease. Genetic anticipation is also observed in susceptible families with the development of earlier onset and more severe disease in the offspring of affected parents in subsequent generations.
Animal models have also aided in our understanding of the pathophysiology of the disease. A variety of genes affecting the adaptive and innate immune systems and epithelial function can all lead to colitis, and a single gene alteration can lead to variable clinical presentations depending on the mouse strain. In addition, a germ-free environment is protective against IBD development in some animal strains.
Genome-wide association studies have found more than 100 distinct susceptibility loci for IBD. Studies analyzing the function of proteins encoded by these genes have provided insights into underlying mechanisms for disease development. The IBD1 gene encodes for the nucleotide-binding oligomerization domain-containing protein 2 (NOD2) (also known as caspase recruitment domain-containing protein 15 [CARD15]) protein, which is associated with ileal Crohn disease. Mutations in this protein lead to problems with intracellular innate immune pathways involved in recognizing microbial products in the cytoplasm. ATG16L1 , IRGM , and LRRK genes regulate the autophagy pathway, which recycles intracellular organelles and removes intracellular microorganisms. Problems with regulating adaptive immune function have been found with alterations in the IL23R , IL12B , STAT3 , JAK2 , TYK2 , IL27 , and TNFSF15 genes. In addition to alterations in immune function, Crohn disease is associated with mutations in proteins important to epithelial cell function, such as the XBP1 and NOD2 genes. Although these gene alterations are found in some patients with Crohn disease, there is no current standard for genetic testing of patients or their family members if a Crohn diagnosis is being considered.
Natural History and Pathophysiology
Experts agree that both environmental and genetic factors contribute to alteration in mucosal integrity of the gastrointestinal tract. In addition, complex alterations in local and systemic immune response lead to varying presentations of Crohn disease. There are two distinct phases of Crohn disease: active disease and remission. Disease severity varies widely from asymptomatic, post-treatment remission to asymptomatic, mild, moderate, or severe active disease.
Cohort studies have found that only 10% to 20% of patients with Crohn disease have prolonged remission after their initial presentation with active disease. If a patient has a year-long remission of their disease, there is an 80% chance that they will remain in remission for subsequent years. Unfortunately, the majority of patients (53%) develop strictures or penetrating disease by 10 years of follow-up, as demonstrated in Fig. 75.1 . Patients who present at a younger age (<40 years old), have perianal or rectal lesions, smoke, have low education level, or require steroids for their initial treatment course are at risk of having a severe course of disease over their lifetime. The majority of patients with perianal fistulas who receive medical or surgical therapy recur at a rate of 59% to 82%.
Up to 80% of patients with Crohn disease will require a surgical intervention during their disease course. Surgical care is reserved for patients who do not respond to medical therapy or those who develop complications (e.g., abscess, fistula, or stricture). Less than 2% of patients have been reported to undergo an intestinal operation within the first year of diagnosis; however, this rate increases over time to up to 17% at 5 years and 28% at 10 years after diagnosis. The relapsing and remitting course of Crohn disease requires that patients understand the need to seek medical attention if they are having symptoms requiring urgent attention. With improved medical therapies, multidisciplinary specialty teams who understand the disease course and improvements in therapy with tailored treatments to achieve the best outcome given the profile of the patient's disease course, Crohn specialists might reduce the need for invasive surgical treatments.
Long-term survival of patients with Crohn disease is very good, with 20-year survival reported at 93% to 94%; however, quality of life scores in patients with Crohn disease are worse than healthy individuals and worse than patients with ulcerative colitis. Several studies have found that there are disease-independent factors that influence the quality of life perceived by Crohn disease patients, including gender, smoking status, perceived stress, psychiatric comorbid disease, social support, coping mechanisms, and patient personality. Importantly, remission of the disease improves quality of life, whether it is achieved through medical or operative management. Long-term, longitudinal quality of life assessments comparing surgical and medical treatment modalities are needed to understand the durability of these findings.
The cost of this chronic disease should also be understood by clinicians in an effort to understand the burden placed on patients. As a chronic disease, Crohn disease is very costly due to the direct expenses of medical and surgical treatments and hospitalizations. However, one should not overlook the indirect and opportunity costs from the disease due to days missed at work by the patient, as well as their caretakers. Similar to other chronic diseases, being aware of this cost is important because the financial hardship placed on patients and families can affect compliance with treatment or cause delays in presentation for medical care leading to poorer outcomes.
Clinical Presentation
Crohn disease is a heterogeneous problem in its disease presentation and course. There are a variety of gastrointestinal and extraintestinal manifestations, which can make each patient's presentation unique. This variability in disease presentation makes diagnosis difficult in some patients. The majority of patients (70%) are diagnosed within 1 year of symptom onset; however, 14% of patients have a delay in diagnosis of 5 years. This is especially true in older patients who are less likely to be referred to specialty clinics.
The majority of patients present with complaints consistent with small bowel or colonic disease, and many patients have pain at the same location over time. In contrast, the behavior of the disease tends to progress over the course of the patient's disease from inflammatory to stricturing or penetrating lesions. Patients with ileocolonic or colonic disease tend to progress to penetrating disease over time, whereas patients with small bowel disease tend to progress to stricturing disease. Complications are common long term, with 94% of terminal ileal disease patients and 78% of colonic disease patients experiencing a complication at 20 years.
The symptoms expressed by the patient are related to the pathology of the disease (i.e., inflammation, stenosis, abscess, or fistula). Abdominal pain is usually mild and diffuse with inflammation but can be colicky with underlying obstruction of the small or large bowel. Patients with obstruction often also present with nausea, vomiting, and abdominal distention.
Diarrhea is a common complaint in patients with Crohn disease and can have several etiologies. Impaired fluid absorption by inflamed bowel segments can lead to diarrhea from excessive intraluminal fluid content. Terminal ileal inflammation or resection can lead to bile salt malabsorption and subsequent diarrhea. Finally, patients who have lost a large portion of their small bowel through disease and/or surgical resection can exhibit steatorrhea due to bile salt deficiency, leading to fat malabsorption.
Fistula formation is a common complaint in patients, with Crohn disease with one-third of patients developing a fistula within 10 years of disease presentation and half of patients developing a fistula within 20 years of disease presentation. The most common sites for fistulas in Crohn disease are enterovesical (intestine to bladder), enterocutaneous (intestine to skin), enteroenteric (intestine to intestine), and enterovaginal (intestine to vagina). However, not all sinus tracts turn into fistulas. Many sinus tracts develop into phlegmons or abscesses.
Severe, acute hemorrhage in patients with Crohn disease is rare (<10% of patients). However, occult bleeding is reported in up to 24% of patients with Crohn disease. Bleeding most commonly occurs in patients with colon disease, but it can occur in patients with inflammation in any location of the gastrointestinal tract.
Perianal disease is frequently seen in patients with Crohn disease. This problem is addressed elsewhere in this book; however, it is important to note that perianal involvement occurs in 10% of patients as the initial symptom of disease and is the sole location of disease in approximately 5% of patients. Approximately 30% of Crohn patients will experience perianal disease at some point in their disease course.
Due to the systemic nature of this inflammatory disease, there is often a general prodrome associated with active Crohn disease. Weight loss can occur due to malnutrition from malabsorption of diseased bowel segments or due to anorexia from the systemic immune response. It is important to be mindful of this potential problem when considering resection of the small bowel in operative management of this disease. This is especially important in patients who present with Crohn disease requiring surgical interventions at a young age. Fatigue and malaise are also common complaints that are thought to occur due to an imbalance in inflammatory mediators and immune cells in the systemic circulation. Fever can occur due to ongoing inflammation and dysregulation of the immune system; however, it is important to note that high fevers could be due to active infections, such as uncontrolled abscesses.
Extraintestinal manifestations of Crohn disease are reported with wide overall incidence (6% to 40%), depending on the study population. They occur due to the inflammatory nature of Crohn disease. The most common extraintestinal manifestations are arthritis (20%), eye involvement (e.g., iritis/uveitis; 5%), skin disorders (e.g., pyoderma gangrenosum and erythema nodosum; 10%), primary sclerosing cholangitis (5%), secondary amyloidosis (rare), and thromboembolic disease due to hypercoagulability.
Disease Classification
There are several ways to categorize Crohn disease: by age of onset, disease location, and disease behavior (phenotype). Variations in the natural history and clinical features of the disease affect our understanding of the patient's prognosis and treatment options. The Vienna classification system is used to objectively classify Crohn disease patient subgroups by considering the patient's age (<40 or ≥40), disease location (terminal ileum, colon, ileocolon, upper gastrointestinal), and disease behavior (inflammatory, stricturing, penetrating). Ongoing research using this classification scheme could improve our understanding of patient outcomes in more detail, allowing us to better tailor future therapies to specific patient subgroups.
Testing
The goal of testing in Crohn disease is to (1) confirm the diagnosis, (2) identify the location, extent, and severity of lesions, (3) evaluate for extraintestinal manifestations, and (4) determine the most appropriate course of treatment. The differential diagnosis of Crohn disease includes a wide range of disorders of the gastrointestinal tract, including other IBDs (i.e., ulcerative colitis), irritable bowel syndrome, lactose intolerance, infectious colitis, appendicitis, diverticulitis, diverticular colitis, ischemic colitis, carcinoma, lymphoma, chronic ischemia, endometriosis, and carcinoid. Diagnosis requires the clinician to evaluate the patient's clinical history and physical exam, laboratory studies, endoscopy, radiographic findings, and histopathologic findings.
Laboratory Studies
Blood tests that are useful in the evaluation of patients with possible Crohn disease include testing for general inflammatory markers and anemia. Standard tests that are routinely obtained for patients being considered for Crohn disease diagnosis include complete blood count, blood chemistry (including electrolytes, renal function tests, liver enzymes, and blood glucose), erythrocyte sedimentation rate, C-reactive protein, serum iron, and vitamin B 12 levels. In addition, there are some unique serum antibodies that can be measured.
General laboratory findings in patients with active inflammation include an elevated white blood cell count, platelet count, erythrocyte sedimentation rate, and C-reactive protein. All of these studies lack specificity but can be helpful in monitoring patients for changes in the level of inflammation of the disease over time.
There are a number of antibodies that have been used in testing for IBD; however, these antibodies have low specificity for Crohn disease. For example, anti- Saccharomyces cerevisiae antibodies are found in 48% to 69% of patients with Crohn disease and 5% to 15% of patients with ulcerative colitis. Perinuclear antineutrophil cytoplasmic antibodies are found in only 5% to 20% of patients with Crohn disease and 48% to 82% of patients with ulcerative colitis. In addition, the anti-OmpC antibody has been identified in 46% of patients with Crohn disease. Although these antibodies might be more suggestive of one IBD over another, no serologic test has been identified that can discriminate between these diseases. Therefore caution should be used in recommending the use of these tests and in interpretation of their findings.
Other tests that are currently under investigation are genetic and stool markers. Genetic testing for the IBD1 gene, which encodes the NOD2/CARD15 protein, is not currently recommended by any clinical society. Mutations in this gene are infrequent in patients with Crohn disease, and the inheritance pattern of the gene is not strictly mendelian. Stool markers for intestinal inflammation, including fecal calprotectin and lactoferrin, have shown promise for identification of patients with IBD. These are increasingly being used in clinical practice, especially as an indication of acute inflammatory activity.
Endoscopy
There are advantages to both endoscopy and radiography, depending on the clinical scenario. Endoscopy allows the clinician to observe mucosal lesions with very good resolution so that even subtle mucosal lesions with mild inflammation can be appreciated. The upper gastrointestinal tract can be evaluated with esophagogastroduodenoscopy, and the lower intestinal tract can be evaluated with ileocolonoscopy. Endoscopy also affords the examiner the ability to perform biopsies to obtain tissue for histologic examination and allows for intraluminal therapeutic interventions, such as endoscopic balloon dilation with or without steroid injections for intestinal strictures. In addition, patients with long-standing colitis from Crohn disease are at risk for cancer formation; therefore colonoscopic cancer surveillance should be performed in these patients.
When chronic diarrhea is the presenting complaint and the clinical evaluation is suggestive of IBD, ileocolonoscopy is a good first line choice for evaluation. It allows the examiner to evaluate the extent, severity, and location of mucosal changes throughout the colon and distal ileum. In addition, biopsies can be obtained throughout the colon and ileum to evaluate for histologic changes consistent with IBD. The colonoscopic findings that are most consistent with Crohn disease rather than ulcerative colitis are aphthous ulcers, cobblestoning, and skip or discontinuous lesions. Rectal sparing and involvement of the terminal ileum also suggest Crohn disease rather than ulcerative colitis, which classically starts in the rectum with continuous inflammation moving proximally. However, there are caveats to these findings in both diseases.
Patients with Crohn disease who have upper gastrointestinal symptoms should undergo esophagogastroduodenoscopy to evaluate for proximal lesions. Although Crohn disease was historically thought to infrequently involve the proximal gastrointestinal tract, there are increasing numbers of reports of concurrent and isolated Crohn disease in this location.
There are endoscopic scoring systems that have been developed to describe the severity of Crohn disease as seen on endoscopy. One such score is the Crohn's Disease Endoscopic Index of Severity (CDEIS) score; however, it is a complex scoring system, which limits its usefulness in daily practice. The Simplified Endoscopic Activity Score for Crohn's Disease (SES-CD) is a simpler scoring system, which rates the (1) presence and size of ulcers, (2) extent of ulcerated surface, (3) extent of affected surface, and (4) presence and type of narrowing. These four characteristics are scored from 0 to 3 in each area of the large intestine (rectum, left colon, transverse colon, or right colon) and ileum. This scoring system has been found to be reproducible among providers; however, there is no agreement on a cutoff score to define disease remission. Another scoring system, the Rutgeerts score, is used to grade lesions recurring at the site of an anastomosis or neoterminal ileum. This score is meant to predict the likelihood of symptomatic recurrence of Crohn disease after curative resection.
Wireless Video Capsule Endoscopy
Wireless video capsule endoscopy is being increasingly used to evaluate for small bowel Crohn disease, which is present in 70% of patients. During the course of this 8-hour study, two images are acquired every second, yielding around 50,000 images in total. Patients are able to continue their normal daily activities while the images are being obtained. Movement of the capsule through the gastrointestinal tract relies upon peristalsis and complete evaluation of the small intestine is achieved in 65% to 80% of patients. Patients with suspected intestinal strictures are recommended not to undergo this study because the capsule may not be able to pass through the narrowing, necessitating surgical removal. Patency capsules to test for severe narrowing due to strictures can be used prior to use of this technology to ensure that it will not become lodged during the examination. Actual reported rates of surgical or endoscopic retrieval of wireless endoscopy capsules due to stricture are as low as 0% to 15% in studies of Crohn disease patients. Although this examination might continue to improve and evolve with new advances in technology, current cost-effectiveness studies have recommended against the use of this study as a third examination if ileocolonoscopy and computed tomography (CT) enterography or small bowel follow-through are found to be negative.
Radiographic Studies
Gastrointestinal imaging studies in Crohn disease have been very useful in documenting the length and location of strictures in areas not easily accessible by endoscopy, especially the small intestine. Many preferences regarding imaging in gastrointestinal disorders reflect local experience and are hospital specific. Traditionally, barium contrast studies, including barium enema or upper gastrointestinal series with small bowel follow-through were performed to assess for narrowing in the gastrointestinal lumen. The current standard of care has evolved with most centers using CT or magnetic resonance (MR) enterography to evaluate for gastrointestinal changes related to Crohn disease.
Due to the chronic nature of Crohn disease, clinicians should take note of the amount of ionizing radiation provided to these patients. This is especially important in patients who are diagnosed with Crohn disease at a young age. Contrast-enhanced ultrasound and MR imaging (MRI) techniques should be considered to reduce the lifetime cumulative exposure to ionizing radiation.
Ultrasound
Transabdominal ultrasound is an infrequently used imaging modality for Crohn disease in the United States compared with European health care settings. It has many reported advantages, including lower cost, wider availability, noninvasiveness, and lack of ionizing radiation. Intraluminal and intravenous contrast agents have been used in some clinical settings with reports of improved image quality of Crohn disease intestinal lesions. Drawbacks to the use of transabdominal ultrasound as a diagnostic study for intestinal lesions include its poor visualization in patients who are obese or with intraluminal gas. In addition, image quality is dependent on the technical ability of the operator, which can lead to poor reproducibility of images in different settings.
Small Bowel Follow-Through and Enteroclysis
Enteroclysis is an imaging study that uses a barium contrast suspension that is directly introduced into the small intestine using a tube. It is similar to the small bowel follow-through study, which uses the same barium contrast suspension that is swallowed by the patient. Evaluation of the two techniques have found that enteroclysis is more uniform in contrast delivery; however, this is at the cost of discomfort to the patient. Although enteroclysis appears to provide better mucosal detail, it does not allow for evaluation of the stomach or duodenum. Preference for either technique appears to be due to institutional support and provider preferences. Evaluation of the small intestine using these techniques can reveal several features of Crohn disease, including ulcers, fissures, fistulas, sinus tracts, cobblestoning, thickened mucosal folds, wall thickening, ileocecal valve enlargement, extent and location of intestinal narrowing and dilation, and skip lesions ( Fig. 75.2 ). The diagnostic sensitivity and specificity of small bowel enteroclysis for Crohn disease has been reported to be as high as 100% and 98%, respectively.
Traditional Computed Tomography and Computed Tomography Enterography
Traditional CT and CT enterography can both be used in the diagnosis of Crohn disease lesions and their complications. Traditional CT uses barium contrast solution and cannot evaluate subtle mucosal lesions associated with early inflammatory Crohn disease. However, this traditional imaging study can be used to identify transmural, extramural, or extraintestinal disease ( Fig. 75.3 ). Intravenous and intraluminal contrast agents should be used to improve clinician's ability to see lesions and the intestinal anatomy in this cross-sectional imaging study. A variety of intraluminal contrast agents have been used in CT (e.g., diatrizoate meglumine and methylcellulose) to distend the bowel lumen. It is important to note that for all of these studies, if the bowel lumen is not completely distended, the flattened loops could be mistaken for abscesses, masses, strictures, or thickened segments of bowel . CT enterography is a newer radiographic technique that uses a neutral contrast agent. This allows for better evaluation of the wall of the small bowel, leading to higher accuracy in detection of inflammation associated with Crohn disease.
Traditional Magnetic Resonance Imaging and Magnetic Resonance Enterography
Similar to the limitations of traditional CT, traditional MRI cannot evaluate for subtle mucosal lesions associated with early Crohn disease. However, MRI is effective in delineating transmural, extramural, or extraintestinal disease. Similar to other cross-sectional imaging techniques, intravenous and intraluminal contrast agents can be used to improve clinician's ability to see lesions and the intestinal anatomy. Isoosmolar polyethylene glycol solution and dilute barium have been used in traditional MRI contrast studies. MR enterography using a neutral contrast agent has the advantage of improved visualization of the small bowel.
Both MRI and CT can provide information regarding: the length of involved segments, presence of skip lesions, wall thickening (>2 mm for small intestine and >3 mm for colon), areas of enhancement (active lesions) and attenuation (target sign), stenotic lesions (intraluminal diameter of <2.5 cm with possible proximal dilation), abscess, phlegmon, fistula (less sensitive than traditional enteroclysis), creeping fat in the mesentery, increased vascularity of vasa recta (comb sign), and mesenteric adenopathy (3 to 8 mm are inflammatory; >10 mm concerning for carcinoma or lymphoma).
Early lesions are not usually able to be identified using traditional CT or MRI. The sensitivity and specificity of both CT and MRI for the diagnosis of Crohn disease are reported to be 94% and 95%, respectively. Studies have found that CT and MR enterography have similar accuracy in the identification of disease location, wall thickening and enhancement, enlarged lymph nodes, and involvement of mesenteric fat; however, MR enterography has demonstrated improved accuracy in the detection of strictures related to Crohn disease. In addition, MRI has the added advantage of being free of ionizing radiation. This is an important consideration for patients who will have multiple imaging studies over their lifetime due to the chronic, recurrent nature of Crohn disease. MR enterography has been touted for its ability to distinguish active inflammation from more chronic fibrosis, an important distinction when deciding the best treatment for individual patients. Refinements in imaging modalities in the future will hopefully provide better ways for the clinician to determine the degree of active inflammation versus chronic scar in patients with Crohn disease.
Pathology
Full-thickness inflammatory lesions can arise from any part of the gastrointestinal tract, from the mouth to the anus. The most common site of Crohn disease is the ileocecal area, with the majority of patients (80%) having some small bowel involvement. Approximately one-third of patients have disease confined to the small intestine, and 20% have disease confined to the colon. Approximately one-third of patients have perianal disease. Involvement of the upper gastrointestinal tract was historically thought to be rare in Crohn disease; however, increased rates of upper endoscopy and biopsy in these patients reveal a high disease prevalence. As many as 50% of patients have active disease on biopsy despite lacking reported symptoms. Involved tissue is most commonly identified in the gastric antrum or duodenum. The esophagus and other regions of the stomach are rarely affected.
Gross Features
There are two distinct phases of Crohn disease, which can be seen on pathologic examination. The active phase of the disease is identified when inflammatory changes are present in the tissue. Active lesions begin as small, flat, soft aphthous ulcers with a pale, white center and surrounding erythema. These lesions deepen into transmural inflammatory lesions, leading to abscesses and fistulae. When the tissue heals and scars, strictures can form obstructive lesions at the site of previous inflammation. In contrast to other IBD, Crohn disease lesions can occur as scattered “skip” lesions with islands of normal mucosa between, leading to a cobblestone appearance ( Fig. 75.4 ). It is important to note that these lesions can coalescence into a continuous pattern similar to that seen with ulcerative colitis. In addition to the cobblestone appearance, other classic descriptions of intestinal lesions include bowel wall and mesenteric thickening, in some patients resulting in narrowing of the lumen. A distinctive feature of Crohn disease is “creeping” of the mesenteric fat, a feature best seen grossly at the time of surgical exploration ( Fig. 75.5 ). In addition, mesenteric thickening from fat thickening and enlarged lymph nodes are also common features of Crohn disease. The remission phase occurs after the inflammatory phase and is identified by healing and fibrosis of the previously inflamed tissue. As the tissue heals, fibrosis can lead to stenosis of the intestinal lumen.
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