Surgical pathology of Crohn's disease

Deep learning model to differentiate Crohn's disease from intestinal tuberculosis using histopathological whole slide images from intestinal specimens

Crohn's disease (CD) and intestinal tuberculosis (ITB) share similar histopathological characteristics, and differential diagnosis can be a dilemma for pathologists. This study aimed to apply deep learning (DL) to analyze whole slide images (WSI) of surgical resection specimens to distinguish CD from ITB. Overall, 1973 WSI from 85 cases from 3 centers were obtained. The DL model was established in internal training and validated in external test cohort, evaluated by area under receiver operator characteristic curve (AUC). Diagnostic results of pathologists were compared with those of the DL model using DeLong's test. DL model had case level AUC of 0.886, 0.893 and slide level AUC of 0.954, 0.827 in training and test cohorts. Attention maps highlighted discriminative areas and top 10 features were extracted from CD and ITB. DL model's diagnostic efficiency (AUC = 0.886) was better than junior pathologists (*1 AUC = 0.701, P = 0.088; *2 AUC = 0.861, P = 0.788) and inferior to senior GI pathologists (*3 AUC = 0.910, P = 0.800; *4 AUC = 0.946, P = 0.507) in training cohort. In the test cohort, model (AUC = 0.893) outperformed senior non-GI pathologists (*5 AUC = 0.782, P = 0.327; *6 AUC = 0.821, P = 0.516). We developed a DL model for the classification of CD and ITB, improving pathological diagnosis accuracy effectively.

The detection rate of granulomas differs between intestinal segments and lesions in Chinese patients with Crohn's disease

BACKGROUND

Crohn's disease (CD) is characterized by non-caseating intestinal granulomas. However, the reported detection rate of granulomas on endoscopy is low. This study aimed to analyze the differences in the detection rate of granulomas in different intestinal segments and lesions in Chinese patients with CD to improve the detection rate of granulomas in clinical practice.

PATIENTS AND METHODS

113 patients with CD were analyzed retrospectively. Patients were divided into two groups: those with (n = 51) and without granulomas (n = 62) on endoscopic biopsies. Clinical information was collected from the medical records, including age; erythrocyte sedimentation rate (ESR); C-reactive protein (CRP), albumin, and hemoglobin (Hb) levels; platelet count; disease course; sex; smoking history; related operation history; Montreal classification; and lesion location, size, and shape.

RESULTS

The detection rates of granulomas in different lesion shapes were significantly different (P < 0.001), with those of longitudinal ulcers and circular ulcers being higher than those of erosion and irregular ulcers. We also found that the detection rates of granulomas in ascending colon and sigmoid colon were relatively higher than other segments of the intestine, however, the difference was not statistically significant (P = 0.716). Additionally, age, sex, smoking history, Montreal classification, related surgical history, disease course, and serum biochemical indicators (ESR; platelet count; and CRP, albumin, and Hb levels) were not significantly different between the two groups.

CONCLUSIONS

The detection rate of granulomas in patients with CD is related to the morphology of the intestinal lesions. Meanwhile, lesion location may be correlated with the detection rate of granulomas.

Histologic Diagnosis of Inflammatory Bowel Diseases

Inflammatory bowel disease, including ulcerative colitis and Crohn disease, is an idiopathic chronic inflammatory condition of the gastrointestinal tract. Since neither the clinical manifestations nor the morphologic features of inflammatory bowel disease are pathognomonic alone, the differential diagnosis to consider is relatively broad, and it relies on the synthesis of clinical, endoscopic, and microscopic features. Long-held histologic diagnostic principles include recognizing structural and inflammatory features of chronicity, that is, architectural distortion, basal plasmacytosis, and expansion of the lamina propria lymphoplasmacytic infiltrate. In addition, evaluation of the neutrophilic inflammation and related crypt and epithelial destruction is essential to gauge the activity of the disease. Nevertheless, these features can be difficult to confirm in special settings, including at the inception of the disease or in partially treated cases. This review will explore the classic morphologic features of ulcerative colitis and Crohn disease, followed by a detailed discussion of atypical and diagnostically challenging presentations and a brief review of the clinical aspects necessary for the daily practice of pathologists.

Luminal Narrowing Alone Allows an Accurate Diagnosis of Crohn's Disease Small Bowel Strictures at Cross-Sectional Imaging

BACKGROUND AND AIMS

Current consensus recommendations define small bowel strictures [SBS] in Crohn's disease [CD] on imaging as luminal narrowing with unequivocal upstream bowel dilation. The aim of this study was to [1] evaluate the performance of cross-sectional imaging for SBS diagnosis in CD using luminal narrowing with upstream SB dilation and luminal narrowing with or without upstream dilation, and [2] compare the diagnostic performance of computed tomography [CT] and magnetic resonance enterography [MRE] for SBS diagnosis.

METHODS

In total, 111 CD patients [81 with pathologically confirmed SBS, 30 controls] who underwent CT and/or MRE were assessed. Two radiologists [R1, R2] blinded to pathology findings independently assessed the presence of luminal narrowing and upstream SB dilation. Statistical analysis was performed for [1] luminal narrowing with or without SB upstream dilation ['possible SBS'], and [2] luminal narrowing with upstream SB dilation ≥3 cm ['definite SBS'].

RESULTS

Sensitivity for detecting SBS was significantly higher using 'possible SBS' [R1, 82.1%; R2, 77.9%] compared to 'definite SBS' [R1, 62.1%; R2, 65.3%; p < 0.0001] with equivalent specificity [R1, 96.7%; R2, 93.3%; p > 0.9]. Using the criterion 'possible SBS', sensitivity/specificity were equivalent between CT [R1, 87.3%/93.3%; R2, 83.6%/86.7%] and MRE [R1, 75.0%/100%; R2: 70.0%/100%]. Using the criterion 'definite SBS', CT showed significantly higher sensitivity [78.2%] compared to MRE [40.0%] for R1 but not R2 with similar specificities [CT, 86.7-93.3%; MRE, 100%].

CONCLUSION

SBS can be diagnosed using luminal narrowing alone without the need for upstream dilation. CT and MRE show similar diagnostic performance for SBS diagnosis using luminal narrowing with or without upstream dilation.

Ileocolic anastomotic inflammation after resection for Crohn's disease indicates disease recurrence: a histopathologic study

Objectives: We performed a pathological pilot study to characterize the inflammation at the ileocolic anastomosis as Crohn's disease or ischemia.Methods and materials: Subjects were selected at random from a retrospective database of patients with Crohn's disease and who had undergone an ileocolic resection with subsequent endoscopic assessment of the anastomosis and neo-terminal ileum. Pathology slides from the anastomotic mucosa, either from targeted biopsies or subsequent ileocolic resections, were re-assessed histologically for features of ischemia and of Crohn's disease.Results: Twenty-nine specimens from 8 patients were reviewed, including 12 ileocolic resection specimens and 17 sets of endoscopic biopsies. Twenty-seven of the 29 specimens, accounting for all of the patients, had evidence of CD-like features. In contrast, only 2 specimens, accounting for 2 of 8 patients, had histologic features of ischemia, and both specimens also had Crohn's-like features.Conclusion: To our knowledge this is the first study to specifically evaluate the pathology of ileocolic anastomoses in Crohn's disease. It suggests that anastomotic inflammation is predominantly a manifestation of recurrent Crohn's disease rather than of postoperative ischemia.

Features and perspectives of MR enterography for pediatric Crohn disease assessment

The aim of this paper is to provide indications for performing magnetic resonance enterography (MRE) in Crohn's disease (CD), the essential technical elements of MRE techniques and typical findings in patients with CD. Patients suffering from CD frequently require cross-sectional imaging. By performing MRE, it is possible to obtain results comparable to those obtained with endoscopy in terms of identifying and assessing disease activity and better than other cross-sectional imaging techniques, such as CT, in the evaluation of the fibrosis and complications of disease. The MR imaging of diffusion MR is a technique which enables medical staff to add important additional information and which may replace the use of intravenous contrast agents in the near future. Magnetic resonance enterography is an accurate tool for assessing bowel disease and the various complications associated with CD. The lack of exposure to non-ionizing radiation is an important advantage of this imaging technique, especially in the case of pediatric patients. Familiarity with common and pathognomonic imaging features of CD is essential for every clinician involved in the treatment of inflammatory bowel disease and the care of patients.

Identification of pathologic features associated with “ulcerative colitis-like” Crohn’s disease

AIM: To identify pathologic features associated with this “ulcerative colitis (UC)-like” subgroup of Crohn’s disease (CD).

METHODS: Seventeen subjects diagnosed as having UC who underwent proctocolectomy (RPC) from 2003-2007 and subsequently developed CD of the ileal pouch were identified. UC was diagnosed based on pre-operative clinical, endoscopic, and pathologic studies. Eighteen patients who underwent RPC for UC within the same time period without subsequently developing CD were randomly selected and used as controls. Pathology reports and histological slides were reviewed for a wide range of gross and microscopic pathological features, as well as extent of disease. The demographics, gross description and histopathology of the resection specimens were reviewed and compared between the two groups.

RESULTS: Patients with “UC-like” CD were on average 13 years younger than those with “true” UC (P < 0.01). More severe disease in the proximal involved region and active ileitis with/without architectural distortion were observed in 6 of 17 (35%) and 7 of 17 (41%) “UC-like” CD cases, respectively, but in none of the “true” UC cases (P < 0.05). Active appendicitis occurred in 8 of 16 (50%) “UC-like” CD cases but in only two (11%) “true” UC cases (P < 0.05). Conspicuous lamina propria neutrophils were more specific for “UC-like” CD (76% vs 22%, P < 0.05). In addition, prominent lymphoid aggregates tended to be more common in “UC-like” CD (P = 0.07). The “true” UC group contained a greater number of cases with severe activity (78% vs 47%). Therefore, the features more commonly seen in “UC-like” CD were not due to a more severe disease process. Crohn’s granulomas and transmural inflammation in non-ulcerated areas were absent in both groups.

CONCLUSION: More severe disease in the proximal involved region, terminal ileum involvement, active appendicitis, and prominent lamina propria neutrophils may be morphological factors associated with “UC-like” CD.

Clinical and pathological analysis of colonic Crohn's disease, including a subgroup with ulcerative colitis-like features

Little is known regarding the clinical and, in particular, pathological manifestations of patients with isolated colonic Crohn's disease. The purpose of this study was to evaluate the clinical and pathological features of patients with Crohn's disease limited to the colon at initial presentation, and to determine whether there are any histological features that are predictive of outcome after surgery. The clinical features, outcome after surgery, and pathological features of colonic resection specimens of 73 patients who presented initially with isolated colonic Crohn's disease were evaluated and compared with 45 Crohn's disease patients who presented initially with both ileal and colonic involvement. Clinically, patients with isolated colonic Crohn's disease presented at a significantly older age at the time of diagnosis, and had a significantly shorter duration of colitis before surgical resection, than did patients with ileocolonic Crohn's disease at disease onset. Pathologically, patients with isolated colonic Crohn's disease showed a significantly higher proportion of cases with subtotal, total, or left-sided colitis, and significantly fewer strictures/stenosis, pericolonic adhesions, pyloric metaplasia, and cases with proximal worse than distal colonic disease. Overall, patients with isolated colonic Crohn's disease showed a trend toward a lower number of major microscopic Crohn's disease features. A small proportion of patients from both Crohn's disease groups (14% and 13%, respectively) showed inflammatory disease limited to the mucosa, without mural involvement, reminiscent of ulcerative colitis, and these were termed 'ulcerative colitis-like Crohn's disease'. These patients were significantly younger than those with mural involvement. Overall, 44% of patients from both Crohn's disease groups developed at least one adverse outcome, and neither the number nor the type of major Crohn's disease features correlated with adverse outcome. Patients with isolated colonic involvement have distinctive clinical and pathological features. A small subgroup of Crohn's patients shows only mucosal involvement reminiscent of ulcerative colitis.

Crohn's disease: a surgeon's perspective

Crohn's disease (CD) is known for wide anatomic distribution, different presentations, life-threatening complications, and multiple modalities of management. Its multiple implications are still unaddressed. Since all the patients do not show a good response to medical modalities of treatment, a significant percentage of these patients are referred to the surgeon for the palliation of complications or for the ultimate curative treatment. Since most surgeons come across such patients only rarely, it is sometimes difficult for them to choose the appropriate procedure at the time of need. Moreover, the various surgical modalities available for the different presentations and complications of the disease have not been adequately discussed. The aim of this review is to offer insight and a detailed account of the management of CD from a surgical perspective. This review offers an overview of the various surgical options available, their utility in context, and an approach to various scenarios of complicated CD.

Pathologist Surgeon Interface in Idiopathic Inflammatory Bowel Disease

To accomplish the important tasks of establishing the diagnosis of inflammatory bowel disease and separating ulcerative colitis from Crohn's disease, there needs to be close cooperation among gastroenterologist, surgeon, and pathologist. Paying close attention to details of sampling and historical information plays a major role in this task, and an equally great role in identifying dysplasia and determining its significance. Important elements in this clinical-pathology interface are discussed in this article.

The role of microbes in Crohn's disease

Despite decades of research, the etiology of Crohn's disease (CD) remains unknown. Its pathogenesis may involve a complex interplay between host genetics, immune dysfunction, and microbial or environmental factors. Microorganisms, including pathogens and members of the indigenous microbiota, may initiate or propagate the inflammatory process in CD. The pathogenesis of CD has been difficult to study, owing to the broad spectrum of typically nonspecific clinical manifestations, the complexity of environmental and genetic factors, the lack of an accurate model of disease, and the limitations of microbiological methods. A more useful and relevant paradigm for the etiology of CD might be based on the idea of a pathogenic microbial community profile and might emphasize the role of interactive sets of microbes, rather than the role of individual organisms. We review how microbes may participate in the pathogenesis of CD and how they may inappropriately activate the mucosal immune system in genetically predisposed individuals.

Validation of 16S rDNA sequencing in microdissected bowel biopsies from Crohn's disease patients to assess bacterial flora diversity

The bowel flora is implicated in Crohn's disease (CD) pathogenesis but its precise role is still unclear. Several non-mutually exclusive hypotheses have been proposed: an unidentified persistent pathogen; excessive bacterial translocation; an immune system abnormality in response to normal bacteria; or a breakdown in the balance between protective and harmful bacteria. These hypotheses can be tested by identifying bacteria in specific microscopic bowel structures or lesions. The present paper describes a novel technique to assess bacterial flora diversity in bowel biopsies, by combining laser capture microdissection with broad-range 16S rDNA sequencing. Fifty-four samples comprising histologically normal and pathological mucosa, MALT, ulcers, submucosal lymphangiectasias, epithelioid granulomas, and lymph nodes were microdissected out of 30 bowel biopsies from five CD patients. Bacterial 16S rDNA was successfully amplified by PCR in all samples, and PCR products from 15 samples were selected for cloning and sequence analysis. A total of 729 bacterial DNA sequences were analysed, which could be attributed to six different phyla (Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, Fusobacteria, and Planctomycetes). DNA from typical bowel bacteria (Enterobacteriaceae, Clostridiales, Bacteroidetes, Fusobacteria) was detected in all microdissected areas. It was thus convincingly demonstrated that 16S rDNA sequencing can be combined with microdissection to study the bowel flora. However, no specific persistent pathogen causal for CD was identified. The results suggest that Enterobacteriaceae may initiate or colonize ulcers in CD. Translocation of bacteria through established mucosal lesions or as a result of increased permeability may be involved in the evolution towards chronic inflammation and in the establishment of persistent lesions. Further study is needed to confirm these preliminary findings.

Polymorphisms in the TNF-alpha promoter and variability in the granulomatous response in patients with Crohn's disease

Granulomas may be found in 30-70% of patients with Crohn's disease (CD). The etiology of granuloma formation in CD is presently unknown. Elevated levels of TNF-alpha are found within granuloma tissue, and are required to maintain granuloma formation in animal models. TNF-alpha production has been shown to influenced by TNF-alpha promoter polymorphisms. We hypothesized that heterogeneity for granulomas in CD might be influenced by the TNF-alpha promoter genotype. Patients with confirmed CD that had undergone full colonoscopy with multiple biopsies and/or surgical resection, served as the study group. One hundred healthy individuals served as a control population for genotyping. Patients and controls underwent genotyping for four TNF-alpha polymorphisms: 238G/A, 308 G/A,857 C/T, and 863 C/A. Inclusion and exclusion criteria were met in 155 patients (1-68 y). Polymorphisms in the TNF promoter were found in 16.6% (238G/A), 14.5% (308 G/A), 36.6% (857 C/T) and 30.7% (863G/A). No significant association was found for any of the individual polymorphisms with presence or absence of granulomas. In conclusion, we did not find an association between individual polymorphisms in the TNF-alpha promoter and presence of granulomas in CD. The reason for heterogeneity in granuloma formation in patients with CD remains elusive.

Association of intestinal granulomas with smoking, phenotype, and serology in Chinese patients with Crohn's disease

INTRODUCTION

Crohn's disease (CD) is a heterogenous disease characterized by variable manifestations and outcomes, and increasing in incidence in China. Phenotypic classification has been proposed to assist in subtyping of disease. Non-caseating intestinal granulomas are a hallmark of CD, but whether intestinal granulomas help predict Chinese CD phenotypes or determine severity, is not known.

AIMS

To determine the association between intestinal granulomas with CD phenotype, severity, risk factors, and serological markers.

METHODS

This was a single-centre study of consecutive definite Chinese CD cases. Granulomas were diagnosed by an experienced GI pathologist. Correlation with the Vienna Classification and other parameters was performed.

RESULTS

Eighty Chinese CD patients were recruited, 40 (50%) of whom had intestinal granulomas. Intestinal granulomas were independently associated with the stricturing behavior (OR: 4.71; 95% CI: 1.41-15.72), colonic location of disease (OR: 26.96; 95% CI: 2.68-271.14), but not with age of CD diagnosis. Current or previous smoking protected against the development of granulomas (OR: 0.16; 95% CI: 0.04-0.59). Granulomas were not associated with peri-anal involvement, extra-intestinal manifestations, anti-neutrophil cytoplasmic antibody or anti-Saccharomyces cerevisiae antibody serology, or severity of CD gauged by the requirement of major intestinal surgery or immunomodulating therapy.

CONCLUSIONS

Intestinal granulomas in the setting of CD may be helpful in determining phenotypic subtypes of CD, but is unhelpful in predicting disease severity. Smoking impairs the formation of granulomas in CD.

A patient with anemia of obscure origin: Crohn's disease in disguise

BACKGROUND

A 65-year-old white Mediterranean male with a 10-year history of intermittent anemia, who was otherwise completely asymptomatic, was referred to our hospital in March 2004. He had a medical history of beta thalassemia and fecal occult blood tests had occasionally been positive.

INVESTIGATIONS

Fecal occult blood test, laboratory investigations, esophagogastroduodenoscopy, colonoscopy with retrograde ileoscopy, mesenteric angiography, small-bowel series, CT scan of the abdomen and pelvis, Meckel's scan, and capsule endoscopy. Laparoscopic surgery followed by macroscopic and microscopic histopathologic examination of samples obtained during the procedure.

DIAGNOSIS

Crohn's disease of the small bowel.

MANAGEMENT

Laparoscopic segmental small-bowel resection with end-to-end anastomosis. Postsurgical treatment with Pentasa 4 g a day.

Diagnostic difficulties in inflammatory bowel disease pathology

This review summarizes some of the common diagnostic problems encountered by pathologists when evaluating patients with chronic colitis and in whom inflammatory bowel disease (IBD) is either suspected or within the differential diagnosis. Both ulcerative colitis (UC) and Crohn's disease (CD) show characteristic, but non-specific, pathological features that may overlap and result in a diagnosis of 'indeterminate colitis' (IC). However, other reasons why pathologists may entertain a diagnosis of IC include failure to recognize or accept certain 'hardcore' histological features as indicative of CD, an attempt to classify cases of chronic colitis based on mucosal biopsy material or in the absence of adequate clinical and radiographic information, and the presence of other disease processes that mask, or mimic, IBD. In addition, some cases of UC may show unusual CD-like features, such as discontinuous or patchy disease, ileal inflammation, extracolonic inflammation, granulomatous inflammation in response to ruptured crypts, aphthous ulcers, or transmural inflammation. Furthermore, other forms of colitis, such as microscopic colitis, diverticulitis and diversion colitis may, on occasion, also show IBD-like changes. The clinical and pathological features that aid in the distinction between these entities, and others, are covered in detail in this review.

Capsule endoscopy findings in patients with established and suspected small-bowel Crohn's disease: correlation with radiologic, endoscopic, and histologic findings

BACKGROUND

Little is known about the accuracy of capsule endoscopy (CE) in evaluation of small-bowel Crohn's disease.

METHODS

Symptomatic eligible patients had ileocolonoscopy and biopsies from the terminal ileum, followed by small-bowel radiologic studies before CE. Endoscopic, radiologic, CE, and histologic findings were compared. Histology (terminal ileum biopsy specimens or a tissue sample after small-bowel resection) served as a criterion standard.

RESULTS

Fifty-four patients were enrolled; 15 of the 54 patients were excluded from data analysis (critical small-bowel strictures, 14, identified on radiology; incomplete CE, 1). Data were analyzed for 39 patients. All patients had histologic evaluation of the small bowel. Final diagnosis of active small-intestine Crohn's disease was made in 29/39 patients (74.4%). When calculated, CE yielded a sensitivity and a specificity of 89.6% and 100.0%, respectively, and a positive predictive value and a negative predictive value of 100.0% and 76.9%, respectively, whereas small-bowel series were 27.6%/100.0% and 100.0%/32.3%.

CONCLUSIONS

CE is more accurate in detecting small-bowel inflammatory changes suggestive of Crohn's disease than conventional studies. CE, combined with ileocolonoscopy, may be proposed as a first-line investigation of the small intestine in cases of uncomplicated known or suspected Crohn's disease.

Inflammatory bowel disease and endothelin-1: a review

Inflammatory bowel disease (IBD) appears to be an inappropriate response to an antigen that leads to chronic inflammation rather than repair. This review looks at the role of endothelin-1 (ET-1) as a proinflammatory agent in IBD. ET-1 antagonists in animal models reduce the incidence and severity of IBD. These antagonists may be useful for treatment of IBD in humans.

NOD2/CARD15 mutations and presence of granulomas in pediatric and adult Crohn's disease

OBJECTIVES

The etiology and mechanism leading to granuloma formation in patients with Crohn's disease (CD) are presently unknown. The first susceptibility gene to be identified as a risk factor for CD is the NOD2/CARD15 gene on Chromosome 16. Mutations in NOD2 could affect the intracellular response to bacterial products and may eventually lead to granuloma formation. The association between NOD2 and granulomas has not been previously explored. We evaluated a possible association between NOD2 mutations and granuloma formation, and compared the prevalence of granulomas in both pediatric and adult cohorts.

METHODS

Patients were consecutively recruited through pediatric gastroenterology and adult gastroenterology programs. Patients were eligible if CD was confirmed, and they had undergone full colonoscopy with biopsy and/or surgical resection. Patients underwent genotyping for NOD2 disease-associated mutations.

RESULTS

A total of 230 patients were enrolled into the study, of whom 169 patients met all inclusion/exclusion criteria (Group 1, 77 patients [age range 1-16 years]; Group 2, 92 patients [age range 17-68 years]). Surgical resection was performed more often in adults (P < 0.005), and gastroscopy was performed more frequently in children (P < 0.001). Granulomas were found in 34% of the patients studied. The prevalence of granulomas did not differ by age, age group, or gender. A disease-associated NOD2 mutation was found in 37.8% of patients. Granulomas were found in 39% of patients with NOD2 mutations compared with 31% of those without NOD 2 mutations (difference was not significant). In addition, no difference was noted for the specific mutations.

CONCLUSIONS

We did not find any correlation between NOD2 mutations and granuloma formation. The cause of granulomas in CD remains elusive.

Diagnostic problems and advances in inflammatory bowel disease

This review summarizes current diagnostic problems and advances with regard to patterns of inflammation and dysplasia in ulcerative colitis and Crohn's disease. Ulcerative colitis and Crohn's disease have a variety of characteristic but non-specific pathologic features. In approximately 5% of inflammatory bowel disease cases, a definite diagnosis of ulcerative colitis or Crohn's disease cannot be established, in which case the term "indeterminate" colitis is used. Most cases of indeterminate colitis are related to fulminant colitis, a condition in which the classic features of ulcerative colitis or Crohn's disease may be obscured by severe ulceration with early superficial fissuring ulceration, transmural lymphoid aggregates, and relative rectal sparing. Approximately 20% of patients with indeterminate colitis develop severe pouch complications, which is intermediate in frequency between ulcerative colitis (8-10%) and Crohn's disease (30-40%). In order to establish a diagnosis of ulcerative colitis or Crohn's disease, it is important to evaluate pathologic material in conjunction with clinical, laboratory, radiologic, and endoscopic features and to recognize the variety of changes that may be seen in fulminant ulcerative colitis. There are a number of exceptions to the classic principles of inflammatory bowel disease pathology that may lead to diagnostic confusion. For instance, apparent skip lesions on biopsy analysis may occur in patients with ulcerative colitis in the following settings; long term oral or topical therapy, focal ascending colon, cecum and/or appendiceal involvement in patients with left sided ulcerative colitis, upper gastrointestinal involvement in patients with ulcerative colitis, and at initial presentation of ulcerative colitis in pediatric patients. In all of these circumstances, the finding of patchy disease and/or rectal sparing should not be misinterpreted as either evidence against a diagnosis of ulcerative colitis, or as representing skip areas characteristic of Crohn's disease. Patients with ulcerative colitis and Crohn's disease are at increased risk for the development of dysplasia and carcinoma. Recent studies suggest that given a similar duration and extent of disease, patients with Crohn's disease have a similar risk of dysplasia and cancer as patients with ulcerative colitis. Dysplasia in ulcerative colitis may be classified as flat or elevated (dysplasia associated lesion or mass [DALM]). Patients with flat high grade dysplasia are generally treated with colectomy. However, there is recent evidence to suggest that patients with flat low grade dysplasia, particularly if detected at the time of initial endoscopic exam, or if its multifocal or synchronous, should also be treated with colectomy. Elevated lesions in ulcerative colitis (DALM) are subdivided into "adenoma-like" and "non-adenoma-like" lesions based on their endoscopic appearance. Recent data suggests that adenoma-like lesions, regardless of the grade of dysplasia, or the location of the lesion (i.e., inside or outside areas of established colitis) may be treated adequately by polypectomy if there are no other areas of flat dysplasia in the patient. Although there are some histologic and molecular features that can help differentiate sporadic adenomas from adenoma-like polypoid dysplastic lesions related to ulcerative colitis, none of these adjunctive techniques can help distinguish these lesions definitively in any single patient. Patients with a non-adenoma-like DALM, (irregular, broad based, or strictured lesion) should be treated with colectomy because of the high probability of adenocarcinoma. The surveillance and treatment options for patients with flat and elevated dysplasia in ulcerative colitis are reviewed in detail.