Immunohistologic diagnosis of orbital lymphoid infiltrates.

The distinction between benign and malignant lymphoid infiltrates of the orbit may be impossible on routine histopathologic sections. However, the detection of monotypic immunoglobulin is useful in distinguishing neoplastic from benign infiltrates. Since diagnostic frozen sections are often performed on biopsies of orbital masses to determine the adequacy of the biopsy and to provide a preliminary diagnosis, we stained additional frozen sections of 20 predominantly lymphoid infiltrates by an immunoperoxidase technique with antisera to immunoglobulin heavy and light chains. On routine sections, nine cases were malignant lymphoma, three were follicular hyperplasia, and eight (42%) were dense lymphocytic infiltrates of indeterminate nature. The nine lymphomas had monotypic immunoglobulin staining. The three histologically benign lesions had polytypic immunoglobulin. Six of the eight indeterminate lesions had monotypic immunoglobulin, supporting a diagnosis of lymphoma; two had polytypic staining. There was evidence of disseminated lymphoma at the time of diagnosis in five of nine patients with histologically malignant lesions and three of five with monoclonal indeterminate lesions for whom the information was available. Staining with monoclonal antibodies to T-cells revealed variable numbers of T-cells in all cases; their number and distribution did not distinguish benign from malignant lesions. The immunoperoxidase technique on frozen sections permits optimal use of small biopsy specimens for both morphologic and immunologic diagnosis. The majority of histologically indeterminate orbital lymphoid infiltrates were shown to be monoclonal.