Definition and Classification of Dysplasia in Ulcerative Colitis

Dysplasia is defined as an unequivocal neoplastic change that is intraepithelial and within confinement of the gland basement membrane or as an unequivocal neoplastic alteration of the colonic epithelium. It may be a marker of carcinoma or may itself be malignant and associated with invasion into the underlying tissue [8].

It is important to realise that, for a very important and practical reason, diagnosing colonic dysplasia is one of the most challenging exercises that the surgical pathologist can go through. This is because the diagnosis of dysplasia is subjective and unless the pathologist sticks to rigid criteria, the diagnosis can be either missed or misdiagnosed. For that reason the Dysplasia Morphology Study Group proposed a broad three-tiered classification scheme for the evaluation of dysplasia. This was designed to alert the pathologist to the histopathological criteria and pitfalls of diagnosing dysplasia, and also to propose treatment and surveillance strategies. The classification consisted of three main categories including (1) negative for dysplasia, (2) positive for dysplasia, either low-grade or high-grade and (3) indefinite for dysplasia (probably negative, unknown or probably positive (Table 1) [8]. The importance of such classifications at that time was to advise a follow-up strategy, which is still used by some centres today. Whilst this classification was met with general acceptance from practicing pathologists in Europe and North America, it was soon discovered that our Japanese colleagues have a lower threshold for using the term cancer in cases in which the tumour has not invaded the muscularis mucosa and to which most European and North American colleagues have given it the term dysplasia. In other words the term cancer is used by one school of practice while the other school

Table 1. Classification of dysplasia [8]

Category

Recommended follow-up

Negative

Regular 1 year

Indefinite

Probably negative

Regular 1 year

Unknown

Short interval

Probably positive

Short interval

Positive

Low grade

Short interval or colectomy if

there is a mass

High grade

Colectomy

prefers the term dysplasia. In most centres in Europe, the term cancer, in regards to the colon, is given only when there is invasion through the biological basement membrane of the colonic epithelium, i.e. the muscularis mucosa. Malignant tumours confined to the mucosa have practically no metastatic potential and therefore we prefer not to use such a term. In 1993, the Research Committee on Inflammatory Bowel Disease of the Ministry of Health and Welfare of Japan [9] proposed a variation of the classification of Riddell et al. (Table 2); however, it was not universally used. Riddell's classification of dysplasia remained unchanged until 2000 when a group of gastrointestinal pathologists from Europe, Japan and North America gathered in Vienna to propose a new classification to bridge the huge gap between the terminologies used by the various groups. The Vienna classification categorises epithelial dysplasia, found any where in the gastrointestinal tract including the colon, as negative for dysplasia, indefinite for dyspla-sia, low- and high-grade mucosal neoplasia and sub-mucosal or deeper invasion by carcinoma (Table 3) [10]. Regarding this classification, high-grade mucosal neoplasia encompassed the following categories including dysplasia, non-invasive carcinoma and suspicious for invasive carcinoma. However, intramucosal carcinoma was included in category 5

Table 2. Histopathological classification of neoplastic epithelium in UC [9]

Category

Description

Inflammatory Indefinite

Probably inflammatory Probably neoplastic Neoplastic but non invasive Carcinoma

(carcinoma) of the original Vienna classification but then later was moved into category 4 (high-grade dysplasia) in the revised Vienna classification [11]. Schlemper and Iwashita subsequently summarised the revised Vienna classification in a review article in 2004 [12]. We feel that the original classification of dysplasia by Riddell et al. has stood the test of time and we recommend using it in conjunction with the revised Vienna classification [11,12].

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