Assessment of epithelial dysplasia in ulcerative colitis has been hindered by inconsistencies
in and disagreements about nomenclature and interpretation. To resolve these issues,
pathologists from ten institutions participated in three exchanges of multiple slides
and, following each exchange, in discussions of the results. A classification system
for the epithelial changes that occur in ulcerative colitis was developed, which should
be applicable to other forms of inflammatory bowel disease as well. The classification
makes use of standardized terminology, addresses specific problem areas, and offers
practical solutions. The reproducibility of the system was studied by means of examinations
of both inter- and intra-observer variations. The clinical implications of the findings
were incorporated into suggestions for patient management. The basis of the classification
is that the term "dysplasia" is reserved for epithelial changes that are unequivocally
neoplastic and may therefore give rise directly to invasive carcinoma. Specimens are
categorized as negative, indefinite, or positive for dysplasia. The negative category
includes all inflammatory and regenerative lesions and indicates that only continued
regular surveillance is required. The indefinite category is applied to epithelial
changes that appear to exceed the limits of ordinary regeneration but are insufficient
for an unequivocal diagnosis of dysplasia or are associated with other features that
prevent such unequivocal diagnosis. Clinically, it indicates that early repeat biopsy
is often required to assess the changes more accurately. The positive category is
divided into two subcategories: 1) high-grade dysplasia, for which colectomy should
be strongly considered after confirmation of the diagnosis, and 2) low-grade dysplasia,
which also requires confirmation and early repeat biopsy or colectomy, depending on
other findings.