Diagnosis of orbital and periorbital tumors. Use of monoclonal antibodies to cytoplasmic antigens (intermediate filaments).
Histopathology provides a definitive diagnosis in the majority of orbital and periorbital tumor biopsies. Occasionally, a tumor cannot be diagnosed by conventional histopathologic means, or the diagnosis is suspect. Special stains have been the primary diagnostic alternative in the past; more recently they have been supplemented with electron microscopy. Immunocytochemistry, classification using monoclonal antibodies to specific cellular antigens, has added a new modality to pathologic diagnosis. Immunocytochemistry can aid in diagnosis in three ways: (a) suggestion of a firm diagnosis, (b) selection from a histopathologic differential, or (c) direction for further evaluation such as special stains or electron microscopy. Immunocytochemistry rarely provides a definitive diagnosis but instead confirms the histopathologic diagnosis. Intermediate filaments are cytoplasmic antigens to which monoclonal antibodies are available. Five antigenically distinct groups of intermediate filaments can help classify tumors derived from mesenchymal, muscle, epithelial, glial, or neural cells. Six cases of orbital or periorbital tumors are presented, which demonstrate the usefulness of intermediate filament immunocytochemistry for classification or confirmation of a histopathologic diagnosis.