Oral Mucosa - Hyperplasia, Squamous

Squamous hyperplasia of the oral mucosa is usually seen on the palate (Figure 1, Figure 2, and Figure 3) or gingiva (Figure 4). Squamous hyperplasia is characterized by increased numbers of squamous cells resulting in increased thickness of the squamous epithelium, which may be diffuse or plaque-like or form blunt papillary projections. Hyperkeratosis is frequently seen with squamous cell hyperplasia. Ulceration of the these lesions may be seen and is usually attributed to mechanical abrasion. Proliferative lesions of the squamous epithelium are thought to be on a continuum, progressing from focal hyperplasia to papilloma to invasive squamous cell carcinoma, although the papilloma stage may be skipped, with progress directly from focal hyperplasia to squamous cell carcinoma. Papillomas are superficial tumors with marked acanthosis, hyperkeratosis, and papillary patterns. Papillomas are usually exophytic, although the inverted papilloma grows in a cuplike shape into the underlying stroma. Exophytic papillomas have a vascularized inner core of connective tissue extending from the submucosa (forming a stalklike structure) that is covered by proliferating squamous epithelial cells, which are often keratinized. The sessile shape, well-differentiated appearance of cells, and absence of a prominent stromal component are important in distinguishing hyperplasia from papilloma. Squamous cell carcinomas can be differentiated from hyperplasia in that the neoplastic cells of a squamous cell carcinoma generally have atypical cells with karyomegaly, loss of nuclear polarity, enlarged prominent nucleoli, and increased mitotic figures. Neoplastic squamous cells invade beyond the basement membrane, with islands, cords, and trabeculae of neoplastic epithelial cells extending into the underlying stroma.