Benign Peripheral Nerve Sheath Tumors (Neurofibromas) of the Lacrimal Gland

Abstract

Two patients, a 43-year-old woman and a 62-year-old man, developed benign peripheral nerve sheath tumors (neurofibromas) of the lacrimal gland, in the former case of the deep orbital lobe, and in the latter of the palpebral lobe. A neurogenic tumor was not seriously considered clinically in either case, because of the paucity of previous reports on the occurrence of neural tumors in the lacrimal fossa region. Instead, in the first case a benign mixed tumor was considered the most likely clinical diagnosis, whereas in the second the coexistence of a swelling in the parotid gland raised the possibilities of a lymphoid tumor or a leukemia. Due to unusual light microscopic features, transmission electron microscopy was required to secure unequivocal diagnoses. In the orbital lobe tumor, an encapsulated spindle cell proliferation without nuclear palisading but with focal areas of myxoid change suggested either a cellular benign mixed tumor or a schwannoma. The palpebral lobe lesion displayed a myxoid spindle cell proliferation that had splayed apart the ducts and acinae of the lacrimal gland, to impart the overall appearance of a benign mixed tumor. The ducts, however, were multilaminar rather than possessing the usual double cellular layer seen in classical benign mixed tumors, and the glandular units contained zymogen granules, which are typically not seen in benign mixed tumors. Electron microscopy disclosed in both lesions the presence of interrupted basement membrane material partially surrounding the tumor cells, long spacing collagen (banded basement membrane material), and poorly developed desmosomes, features compatible with a neural tumor. Neither myofilaments, tonofilaments, nor ductal-type granules sometimes observed in benign mixed tumors were discovered. The tumor cells in these cases therefore failed to demonstrate clear-cut Schwann cell characteristics (eg, continuous basement membranes, pseudo-mesaxons, tangles of cell processes), and more closely resembled perineural cells that have been described in ultrastructural studies of peripheral nerve tumors including neurofibromas of other sites.