Primary thyroid lymphoma in the background of Hashimoto thyroiditis

Primary thyroid lymphomas (PTLs) constitute only 1-2% of all extranodal lymphomas and approximately 2-8% of all thyroid malignancies. Thyroid non-Hodgkin lymphoma (NHL), though not common, is curable without the need for extensive surgery. Fine-needle aspiration cytology (FNAC) has become the procedure of choice for the initial diagnosis of thyroid nodule, but there are very few reports of FNAC of PTL in the literature. Most common thyroid lymphomas are diffuse, large, B-cell lymphoma (DLBCL), and mucosa-associated lymphoid tissue lymphoma (MALT). When dealing with DLBCL, the main cytological differential diagnosis to be kept in mind is anaplastic thyroid carcinoma. Differentiating these entities is required at the cytological level as both require different treatments, in fact, DLBCL can be treated by chemotherapy while anaplastic thyroid carcinoma by surgical excision. Diagnosis of MALT, which is a low-grade NHL is difficult on FNAC as it closely resembles Hashimoto thyroiditis (HT). We report herein a case of 52-year-old female, suffering from HT since 10 years, who developed a thyroidal DLBCL. This case emphasizes the role of FNAC as a good diagnostic tool that, followed by Tru-cut biopsy for accurate PTL typing, can avoid the morbidity associated with surgery.