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s may be helpful, benign tumors tend to have a more regular surface and are relatively movable upon palpation; malignant tumors tend to be fixed to adjacent tissue and often have irregular and ulcerated surfaces. However, clinical criteria are totally inadequate for diagnosis of tumorlike lesions.
     Atrophy. Areas of atrophy may appear reddened because the epithelium is thin and the connective tissue vascularity is clearly manifested. The area may be slightly depressed. Special epithelial structures may be replaced by a thin epithelium. For example, atrophy of lingual papillae results in a smooth, red tongue surface.
     Other Lesions. Certain gross lesions that occur on skin are not characteristically seen on oral mucosa. Among these are scars, crusts (dried exudate overlying an ulcerated area), fissures (cracks resulting from drying) , and excoriations (self-inflicted traumatized areas).
DISTRIBUTION AND DURATION OF LESIONS
     In addition to the type of lesion present in a given case, the distribution of the lesion may be significant and may aid in establishing a tentative diagnosis. For example, an eruption of vesicles in the posterior area of the mouth and oropharynx might suggest herpangina, whereas involvement of the anterior area of the mouth and gingiva might suggest herpetic stomatitis. Severe vesicular and bullous lesions on the labial mucosa might indicate erythema multiforme. The duration of lesions may also be suggestive of certain conditions. A history of a recurrent pattern may be valuable in detecting a problem such as aphthous stomatitis.
HIBTOPATHOLOGY OF MUCOSAL LESIONS
     The microscopic picture of mucous membrane disease is rarely diagnostic in itself, but it may present certain features suggestive of or consistent with known disease patterns. The variety of possible alterations affecting epithelium and connective tissue is limited. All changes from normal must be recorded in each case, and the assembled facts may point to a specific diagnosis. In certain lesions such as malignant tumors, a definitive diagnosis can be established by microscopic study.
     Histopathologic features commonly seen in mucous membrane diseases are discussed here in relation to epithelium and connective tissue.
Epithelial Alterations
     Hyperkeratosis. This condition is characterized by a widening or thickening of the stratum corneum. Clinically, hyperkeratosis results in a white lesion. The opacity and whiteness of the lesion are related to the amount of keratinization.
     Paraketatosis. In parakeratosis, the stratum corneum demonstrates persistence of nuclei and varying degrees of thickening that may equal that of hyperkeratosis. This reaction may represent an abnormally rapid keratinization process. Clinically, it usually results in a white lesion.
     Acanthosis. In this condition, the stratum spinosum becomes wider. Acanthosis signifies epithelial hyperplasia; it may exist with or without hyperkeratosis.
     Spongiosis. This term is used to signify intercellular edema of the epithelium, in which intercellular bridges of the stratum spinosum become more prominent.
     Hydropic Degeneration. Because of edema and degeneration of cells of the stratum germinativum, the nuclei are replaced