White sponge nevus. Diagnosis by light microscopic and ultrastructural cytology.

The lesions of white sponge nevus, an autosomal dominant abnormality of squamous epithelial differentiation that primarily affects the oral cavity, may be grossly similar to those of other hereditary mucosal syndromes, infections or preneoplastic/neoplastic processes. This differential diagnosis is best resolved in many cases by exfoliative cytology, interpreted in the context of clinical history and physical findings. The following report describes a case of white sponge nevus with typical clinical and cytologic findings, in which the diagnosis was confirmed by ultrastructural cytology. Light microscopic cytology revealed parakeratotic cells and many cells containing dense eosinophilic intracytoplasmic inclusions. Electron micrographs of exfoliated cells demonstrated that these inclusions are composed of disordered aggregates of tonofilaments.