The epithelium of precursor lesions may be thick, but in the oral cavity it can also be atrophic. By definition, there is no evidence of invasion. The magnitude of surface keratinisation is of no importance. Allocation to categories within each of the classifications requires consideration firstly of architectural features and then of cytology.


Hyperplasia describes increased cell numbers. This may be in the spinous layer (acanthosis) and/or in the basal/parabasal cell layers (progenitor compartment), termed basal cell hyper-plasia. The architecture shows regular stratification without cellular atypia.

Dysplasia, / squamous intraepithelial neoplasia / atypical hyperplasia

When architectural disturbance is accompanied by cytologic atypia, the term dysplasia applies. The terms squamous intraepithelial neoplasia (SIN) and atypical epithelial hyperplasia are used synonymously.

There is a challenge in the recognition of

Table 4.01 Classification schemas that histologically categorize precursor and related lesions

2005 WHO Classification

Squamous Intraepithelial Neoplasia (SIN)

Ljubljana Classification Squamous Intraepithelial Lesions (SIL)

Squamous cell hyperplasia

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