What is the endoscopic definition of BO and how is it described?
What is the endoscopic definition of BO and how is it described?
Barrett’s Oesophagus (BO) is a premalignant condition of the oesophagus defined as the presence of metaplastic columnar epithelium,which endoscopically appears as salmon pink mucosa, extending above the gastro-oesophageal junction (GOJ) and into the tubular oesophagus, thereby replacing the stratified squamous epithelium that normally lines the distal oesophagus.
The columnar type mucosa can be one of three types: gastric-fundic type, cardiac type and intestinal-type. It is the intestinal type that has been clearly shown to predispose to cancer development and therefore most experts agree that an oesophageal biopsy of columnar epithelium above the GOJ showing intestinal type is required to confirm and establish a diagnosis of BO, rather than relying on endoscopy alone. This is discussed in more detail in the section titled What is the histological definition of BO?
Intestinal metaplasia at the cardia
There has been debate in the literature as to whether or not cardiac-type epithelium should be included in the definition of BO. Hence according to the 2011 American Gastroenterological Association (AGA) Technical Review on the Management of Barrett’s Oesophagus “’Barrett’s esophagus’ presently should be used only for patients who have intestinal metaplasia in the esophagus”. This differs from the definition in previous British Society of Gastroenterology in which BO was defined as “an endoscopically apparent area above the oesophagogastric junction that is suggestive of Barrett’s, which is supported by the finding of columnar lined oesophagus on histology.” This was based on the premise that the diagnosis of IM can be limited by sampling error in mucosal biopsies, especially were less than 8 biopsies were taken. More recently the BSG guidelines have been updated, and although admitting that 'barrett's mucosa' without IM has a lower risk of progression to cancer based on the population-based study from the Northen Ireland register, they still recommend that "the presence of IM is not a prerequisite for the definition of Barrett’s oesophagus", and if cardiac type epithelium were present in two subsequent endoscopies in segments <=3cm, these patients can be discharged from further surveillance.
This issue of length of columnar segment with IM and surveillance is discussed in later chapters on recommended surveillance for patients with BO (see also How frequently should patients with BO undergo endoscopy?), however for the purposes of these guidelines, given the population-based study from the Northen Ireland register showning a significantly lower risk of progression to cancer in those patients without intestinal-type epithelium we advocate utilisation of the AGA definition provided that appropriate sampling of the columnnar segment has been performed.
Endoscopic landmarks for a diagnosis of BO
A reliable endoscopic diagnosis of BO depends on the accurate endoscopic recognition of the anatomic landmarks at the GOJ and squamocolumnar junction (SCJ). To standardise the objective diagnosis of endoscopic BO, the Prague C & M Criteria were proposed by a subgroup of the International Working Group for the Classification of Oesophagitis (IWGCO). In this system, the landmark for the GOJ is the proximal end of the gastric folds. Whilst the exact definition of what constitutes the GOJ remains unresolved with no universally accepted definition, the vast majority of published papers on BO have used the proximal extent of the gastric folds, which was first described in 1987 by McClave et.al., and indeed the Prague C & M Criteria have been widely adopted. In the original paper, criteria were externally validated by 29 expert endoscopists and the interobserver agreement, for recognising different lengths of BO and the GOJ location position were very good. This has recently been further externally validated by another group where 16 gastroenterology trainees had similary high interobserver agreement confirming the utility of these criteria by both trainees and experts after adequate training. However recognition of ≤ 1 cm of BO using the Prague C & M Criteria was less reliable, which is the basis for the recommendation of recent BSG guidelines to "suggest that 1 cm (M of Prague criteria) should be the minimum length for an endoscopic diagnosis of Barrett’s (Evidence grade IV)".
In addition, a recent study in Japan has also highlighted the importance of training on Prague criteria. Before adequate training interobserver agreement amongst a group of 25 experienced endoscopists for identification of the GOJ was poor but this improved markedly after training. It should also be noted that a criticism of the Prague criteria are that they may fail to identify short segment BO, a lesion found frequently in most Asian countries. Hence, many Japanese authors believe endoscopic BO is better defined as the most distal extent of the palisade vessels. Given the absence of evidence to advocate the use of one over the other, and the widespread use of Praque C & M Criteria by western endoscopists, we advocate the use of the proximal extent of the gastric folds in defining BO.
The proximal margin of BO in the Prague Criteria are based on measurement of both the circumferential (C) and maximal (M) extent of metaplasia (shown in figures 1 & 2 below). There is less debate regarding this margin and it is defined as maximum extent of columnar epithelium above the GOJ.
Figure 1. Diagrammatic representation of endoscopic Barrett’s Oesophagus showing an area classified as C2M5. C: extent of circumferential metaplasia; M: maximal extent of the metaplasia (C plus a distal “tongue” of 3 cm); GEJ: gastroesophageal junction.
Figure 2. Video still of endoscopic Barrett’s Oesophagus showing an area classified as C2M5. C: extent of circumferential metaplasia; M: maximal extent of the metaplasia (C plus a distal “tongue” of 3 cm).
Source: Images used from Publication Gastroenterology, 131(5), Prateek Sharma, John Dent, David Armstrong et. al, The Development and Validation of an Endoscopic Grading System for Barrett’s Esophagus: The Prague C & M Criteria, p1395-1396, Copyright (2006), with permission from Elsevier
The presence of Barrett’s Oesophagus should be described using the Prague C & M Criteria.
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