Abstract
The aim of this study is to present an elusive case of primary thyroid lymphoma (PTL), initially thought to be anaplastic thyroid carcinoma, then Rosai Dorfman disease, before the final diagnosis of PTL was made. An elderly female with hypothyroidism presented with compressive airway symptoms secondary to an enlarging neck mass. Imaging was suggestive of undifferentiated thyroid cancer. The initial biopsy was unexpectedly consistent with a lymphoproliferative disorder such as Rosai-Dorfman disease. A repeat biopsy with immunohistochemical analysis yielded a diagnosis of diffuse large B-cell lymphoma of germinal center subtype. The patient was spared thyroid surgery and started on appropriate chemotherapy. PTL is within the differential diagnosis that physicians must consider in a patient with a rapidly-enlarging neck mass. A clinical index of suspicion and early accurate diagnosis may spare the patient from unnecessary surgery that is required of most other non-hematopoeitic thyroid malignancies.