Keratinocyte differentiation in acquired cholesteatoma and perforated tympanic membranes.

OBJECTIVE: To evaluate the type of differentiation of keratinocytes of acquired cholesteatoma and its significance for cholesteatoma invasiveness. DESIGN: Forty acquired cholesteatomas and 10 tympanic membranes with persisting perforations were snap frozen and processed for immunohistochemical studies. Cytokeratin antibodies that represented all subgroups and antibodies that were directed against collagen components of the basal lamina were applied. Expression of these constituents was scored by using light microscopy. RESULTS: The phenotype of the matrix was generally characterized by an extension of expression of basal cell cytokeratin 14 and hyperproliferation-associated cytokeratins 6, 16, and 17 into the suprabasal cell layers, while the expression of keratinization marker cytokeratin 10 was down-regulated. These features varied greatly at different sites of the matrix and were most marked at the advancing front of the cholesteatoma. A comparable expression pattern, but less pronounced, was observed at the epidermal front of the mucocutaneous junction of the tympanic membrane perforations. This phenomenon was invariably associated with a mononuclear cell infiltrate in the dermis at both junctions. The basal lamina was always intact. CONCLUSIONS: Acquired cholesteatomas show hyperproliferative features. There is a striking similarity between the pronounced expression of this phenotype and the associated inflammation at the mucocutaneous junctions of cholesteatomas and tympanic membrane perforations and those that are observed after epidermal injury. This indicates that epidermis and middle ear epithelium do not form stable junctions and the front can be considered to be a persisting epidermal defect. This involves the permanent presence of "activated keratinocytes" in the junction area that will lead to proliferation and migration, when additional triggers are present.

Epidermal differentiation in the human external auditory meatus.

The differentiation of epidermis in the various parts of the human ear canal was documented on the basis of cytokeratin (Ck) expression patterns. Immunohistochemistry was performed on cryostat sections of normal meatal skin using a comprehensive panel of monospecific Ck antibodies representing the main lines of epithelial differentiation. The epidermis of the cartilaginous part showed a Ck profile characteristic of normal skin type differentiation. The deep meatal skin, including the tympanic membrane, showed a peculiar type of differentiation: in addition to epidermal Cks, hyperproliferation-associated Cks 6, 16, and 17 were expressed in the suprabasal cells, while the simple epithelia cell marker Ck 19 was found in the basal cells. The presence of hyperproliferative Cks in the deep meatal skin could only partly be related to areas of proliferative activity. Keratinocytes, which express markers of hyperproliferation, are migratory. Therefore, their presence in the meatal skin is likely to be related to the peculiar pattern of keratinocyte migration, the purpose of which is to keep the meatus free from desquamation products.

Squamous metaplasia of the middle ear epithelium.

This study deals with the expression of cytokeratins (Cks) in squamous cell metaplastic lesions in rat and human middle ear. In rats, squamous metaplastic lesions could be induced during chronic otitis media. The histological features of these lesions were similar to those observed in the human middle ear. Immunohistochemistry revealed that squamous cell metaplasia in both rat and human middle ear is characterised by a loss of simple epithelial cell related Cks and the appearance of Cks characteristic of stratified and cornifying epithelia. This indicates a true change in the differentiation of the middle ear epithelium. It is concluded that the Ck profile of the cholesteatoma matrix cannot be used as a variable to decide whether the origin of cholesteatomas is epidermal or metaplastic. This rat model is suitable for studying squamous cell metaplasia in relation to cholesteatoma genesis.

Growth and differentiation of meatal skin grafts in the middle ear of the rat.

OBJECTIVE: To determine the behavior of epidermal cells after transplantation in the middle ear. DESIGN: In a rat model, full-thickness meatal skin grafts were transplanted into the middle ear and studied morphologically and immunohistochemically with the use of antibodies directed against different cytokeratin (Ck) polypeptides, which are markers of different types of epithelial cell differentiation. RESULTS: The grafts had either transformed into epithelial cysts or had become integrated into the middle ear epithelium. The epithelium of the integrated grafts showed gradual transition into the epithelium of the middle ear. A clear distinction between epidermal cells and middle ear epithelium could be made only on the basis of their Ck profiles. The Ck profiles of the grafts revealed a decrease in the expression of epidermal Cks, while nonepidermal Cks became expressed. These changes can be ascribed to replacement of the dermal mesenchyma by mesenchyma from the middle ear. In two ears with superimposed infection, the graft epithelium showed expansive growth. CONCLUSIONS: Meatal epidermis is well tolerated in the middle ear, but superimposed infection can induce expansive growth. These findings favor the concept that the progressive growth of cholesteatoma is related to the presence of inflammatory processes.

Myospherulosis in the operated temporal bone.

Myospherulosis is an unusual foreign-body reaction occurring in tissues exposed to petrolatum-based products. Histopathologically this disorder is characterized by the presence of large and small tissue spaces containing amorphous debris and peculiar sac-like structures enclosing numerous brown spherical bodies. A rare case of myospherulosis of the middle ear and mastoid is presented and the literature is reviewed.

Isolation of Streptobacillus moniliformis from the middle ear of rats.

Streptobacillus moniliformis was isolated from the middle ear of 9 of 16 rats used for otological studies. Examination of rat sera for the presence of anti-Streptobacillus moniliformis antibodies using an ELISA technique resulted in 15 seropositive animals. The source of the S. moniliformis infection was not determined.

Immunohistochemical study of cytokeratin expression in normal and pathologic middle ear mucosa of the rat.

The expression of cytokeratins in the epithelium of the middle ear and external auditory meatus of the rat was studied on cryosections of ethylenediaminetetraacetic acid-decalcified specimens by use of a panel of monoclonal antibodies. The normal middle ear epithelium revealed a complex cytokeratin profile, including regional differences. The induction of sterile middle ear effusions resulted in increased cytokeratin expression. Infective effusions were accompanied by both quantitative and qualitative changes in the cytokeratin expression patterns. The differences observed between the cytokeratin profiles of external meatal skin and those of middle ear epithelium may form a useful tool for research into cholesteatoma development.

Cytokeratins in induced epidermoid formations and cholesteatoma lesions.

The expression of cytokeratins varies with the type of epithelium, the state of differentiation, and pathological conditions. In this study, the differential expression of cytokeratins in external meatal skin and middle ear epithelium was used for a pathogenetic study of cholesteatoma lesions and infection-induced epidermoid formations in the middle ear of the rat. Immunocytochemistry generally revealed an epidermal-type cytokeratin profile in the cholesteatoma matrix, except for the focal expression of nonepidermal cytokeratins at the invasion front. Comparable observations were made in the middle ear of the rat after an infection-induced invasion of epidermal cells from the meatal skin. An infection-induced-cornifying metaplastic lesion of the middle ear epithelium revealed nonepidermal cytokeratin expression. The results of this combined study suggested that the cholesteatoma specimens studied had an epidermal origin. The expression of nonepidermal cytokeratins was considered to result from a state of hyperproliferation rather than from metaplasia.