© 1994 Oxford University Press
"Proliferative Keratin Cyst," a Lesion in the Lungs of Rats Following Chronic Exposure to Para-aramid Fibrils
Cystic and keratinizing squamous lesions have been observed
in rats exposed chronically to a number of particulates. A variety
of diagnostic terms have been applied to these pulmonary lesions
but no consensus exists as to their most proper morphological
classification. In an attempt to obtain a consensus for cystic
keratinizing pulmonary lesions produced in rats by Kevlar para-aramid
fibrils and TiO
2 powder, a panel of medical and veterinary pathologists
was invited to participate in a workshop addressing the morphology
of the lesions and to reach a consensus on a suitable descriptive
diagnostic term. All participants agreed that the cystic keratinizing
lesions were not malignant neoplasms. The majority was of the
opinion that the lesions were not neoplasms. A minority (3/13)
considered the lesions to be benign tumors. The panel considered
that the most appropriate morphologic diagnosis for the lesions
was "proliferative keratin cyst" (PKC). In addition, the panel
agreed on the following descriptive text: "The lesions are cysts
lined by a well-differentiated stratified squamous epithelium
with a central keratin mass. Growth appears to have occurred
by keratin accumulation and by peripheral extension of the metaplastic
change into the adjacent alveolar spaces. The lesions are sharply
demarcated except in those areas in which there has been extension
of metaplasia into adjacent alveoli. The squamous epithelium
has few mitotic figures and dysplasia is absent."
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