Definitions of Histological Abnormalities in Inflammatory Bowel Disease: an ECCO Position Paper

Abstract

Histological assessment of endoscopic biopsies in inflammatory bowel disease [IBD] plays an important role in clinical management, investigative studies, and clinical trials. Scoring schemes consisting of multiple histological items and offering considerable precision are widely available. However, definitions of histological abnormalities are often inconsistent. Furthermore, interobserver variability for their recognition and assessment may be high. The European Crohn's and Colitis Organisation [ECCO] formed an expert panel to explore definitions of histological abnormalities in IBD, with the aim of improving the quality of diagnosis and facilitating development of scoring schemes. The process confirmed that the current definitions often have no evidence base and vary between sources. Using available evidence and expert knowledge, the panel produced a series of ECCO consensus position statements on histological features in IBD.

Keywords: Crohn’s disease; Inflammatory bowel disease; definition; histology; ulcerative colitis.

Figure 1

A well-orientated colorectal biopsy, including muscularis mucosae [stars], is ideal for assessment of mucosal architecture. In normal mucosa, crypts are mostly parallel to each other and the crypt base usually reaches the underlying muscularis mucosae [circle]. An occasional branching crypt [arrow] is acceptable as normal. For all colour figures refer to online version.

Figure 2

A colonic biopsy that shows extensive crypt distortion, including crypt branching and crypt irregularity. In addition, all crypts show atrophy, with shortening [failure to reach the muscularis mucosae; ellipse] and wider spacing [hexagon]. The two most central crypts show severe epithelial mucin depletion [arrows]. Diffuse basal plasmacytosis is present [stars].

Figure 3

Crypt atrophy and crypt distortion are milder here than in Figure 2. Crypt shortening ranges from very mild [circle] to a reduction of almost 50% in length [capsule]. Mild loss of the normal parallel ‘test tube’ arrangement of crypts represents crypt distortion.

Figure 4

A villiform surface in colorectal mucosa [ellipse] is the consequence of wide crypt mouths and irregular regeneration. At the top left there is an erosion [star], defined as injury to the surface epithelium and underlying mucosa without extension deeper than the muscularis mucosae.

Figure 5

Paneth cells [arrows] with characteristic bright red cytoplasm are numerous at crypt bases in the small bowel and are normal in the right colon. By convention, their presence distal to the splenic flexure constitutes Paneth cell metaplasia.

Figure 6

Pyloric metaplasia in ileal mucosa, comprising two glands [ellipse and rectangle] lined by columnar cells with small basal nuclei and pale or clear cytoplasm and resembling gastric pyloric or duodenal Brunner’s glands.

Figure 7

Basal plasmacytosis, comprising an increase in plasma cell numbers at the mucosa base [‘crypts with their feet in pools of plasma cells’] and elsewhere [eg, within large ellipse; small ellipse surrounds three plasma cells]. Other inflammatory cells [eg, eosinophils] are also apparent. The base of a crypt [arrow] shows cryptitis [ie, at least one neutrophil in the crypt epithelium].

Figure 8

Lymphoid aggregates [ellipse around an aggregate] are nodular collections of lymphocytes that typically lie at the base of the mucosa. They are a normal finding in intestinal mucosa. Their number and density may increase in inflammatory bowel disease [IBD], but defining a significant increase is difficult.

Figure 9

Eosinophils accompany basal plasma cells in this biopsy [circles identify four eosinophils]. A crypt shows eosinophil cryptitis [arrow; ie, at least one eosinophil in the crypt epithelium without accompanying neutrophils]. The maximum number of lamina propria eosinophils and of foci of eosinophilic cryptitis in normal mucosa is uncertain.

Figure 10

This crypt abscess [arrow] consists mainly of eosinophils but also includes neutrophils. Therefore, it is a crypt abscess rather than an eosinophil crypt abscess.

Figure 11

A granuloma [circle] in Crohn’s disease [CD] includes at least five histiocytes and does not show necrosis. Here, the number of histiocytes is considerably greater than five. Multinucleate giant cells and a lymphoid cuff are present in some granulomas in CD, but not in this example.

Figure 12

A crypt abscess [arrow] comprises at least two neutrophils in the crypt lumen and may include other inflammatory cells. The deep part of this crypt shows rupture with extrusion of contents, generating a cryptolytic granuloma [circle].

Figure 13

Unlike an erosion, an ulcer extends deep to the muscularis mucosae. In this resection specimen, there is severe ulceration with complete loss of mucosa and with extension into the submucosa [star] and underlying muscularis propria [rectangle]. Distinction from an erosion is easier here than in many mucosal biopsies.

Figure 14

Dysplasia is an unequivocal neoplastic epithelial alteration without invasive growth. The crypt at lower left [ellipse] does not show dysplasia. Most other crypts [eg, within the circle] show low-grade dysplasia, with some resemblance to normal mucosa.

Figure 15

High-grade dysplasia showing severe cytological atypia and severe architectural changes. The latter include a cribriform pattern [ellipse]. The appearances are less reminiscent than low-grade dysplasia of normality.

Figure 16

The term ‘indefinite for dysplasia’ is appropriate when distinction between non-neoplastic epithelial changes and dysplasia is not possible, as in this example of epithelial atypia [capsule] adjacent to an ulcer/erosion [circle].