PERIPHERAL-NERVE SHEATH TUMORS OF THE THYROID-GLAND - A SERIES OF 4 CASES AND A REVIEW OF THE LITERATURE

Primary peripheral nerve sheath tumors (PNSTs) of the thyroid gland ar e exceptionally rare. Two schwannomas and two malignant PNSTs (MPNSTs) , arising primarily within the thyroid gland, were identified in the f iles of the Endocrine Tumor Registry at the Armed Forces institute of Pathology. The patients included two females, age 69 and 80 yr, and tw o males, age 18 and 33 yr. The patients presented with a mass in the t hyroid gland confined to a single robe of the thyroid without involvem ent of the cervical neck region. None of the patients had a history of neurofibromatosis. The benign tumors were encapsulated, one of them c ystic, with the characteristic cellular and nuclear features of schwan nomas. The MPNSTs were invasive tumors, effacing the thyroid parenchym a, with a fascicular pattern of growth composed of neural appearing ce lls with increased cellularity, increased mitotic activity and with fo cal necrosis. Immunoreactivity for S-100 protein and vimentin was seen in all tumors. The patients with schwannomas, treated only by surgica l resection, were alive without evidence of disease, over a period of 5-33 yr. Both patients with MPNSTs died of the disease 8 mo and 42 mo, respectively, with widely disseminated disease. Primary thyroid PNSTs are exceptionally rare tumors. MPNSTs, in this limited experience, ha ve a fatal outcome irrespective of aggressive adjuvant therapy.