Primary Thyroid Mucosa-Associated Lymphoid Tissue (MALT) Lymphoma: A Case Report.

Primary thyroid lymphoma (PTL) is a rare entity. Mucosa-associated lymphoid tissue (MALT) lymphoma represents only a small portion of all PTLs and is usually associated with chronic lymphocytic thyroiditis. Most cases are indolent and asymptomatic, which may delay diagnosis. We present the case of a 63-year-old woman with a history of autoimmune hypothyroidism who developed a rapidly enlarging anterior neck mass and compressive symptoms. Ultrasound revealed an enlarged thyroid gland with a heterogeneous right lobe with a 34 mm lesion suggestive of focal thyroiditis. Fine-needle aspiration cytology was negative for malignancy (Bethesda II). Due to clinical progression, a total thyroidectomy was performed. Histopathological and immunohistochemical analyses confirmed MALT lymphoma. Primary MALT lymphoma of the thyroid is a rare and often underrecognized diagnosis. It should be considered in patients with chronic thyroiditis and new or enlarging nodules. Surgical excision may be both diagnostic and therapeutic in localized disease. Postoperative surveillance remains essential due to the potential for systemic involvement.