PSAT288 Mucosa-associated Lymphoid Tissue Thyroid Lymphoma Presenting as a Rapidly Growing Neck Mass in an Asymptomatic Male Patient

A 77-year-old male was referred to endocrinology for a 2-month history of a rapidly enlarging painless left neck mass. His only other complaint was unintentional weight loss of 10 pounds over 12-months. On exam patient had a firm, smooth, nontender 2 cm thyroid/neck mass extending below left clavicle. No abnormalities were detected for right thyroid gland. There was no palpable lymphadenopathies or hepatosplenomegaly noted. No signs of tracheal, esophageal, or neck vein compression were noted. He did not have any history of radiation exposure, family history of thyroid-related disorders, or malignancy. Laboratory test including complete blood count, comprehensive metabolic profile and TSH were within normal limits. TPO antibody was positive. Ultrasound revealed a 7.7×4.1×4 cm hypoechoic spongiform mass replacing the left lobe of the thyroid, as well as scattered sub centimeter nodules. Contrasted CT of the neck confirmed 6.5×5.2×3.9 cm left thyroid mass causing mild rightward deviation of the trachea and extending into the superior mediastinum and no lymphadenopathy. FNA of the mass revealed presence of crushed lymphoid cells without thyroid follicular cells, which raised the possibility of chronic lymphocytic thyroiditis. FDG- PET scan showed intense, heterogeneous FDG uptake in the left neck mass (max SUV=10.7), likely arising from the left thyroid lobe concerning for thyroid malignancy without evidence of distant metastases. The patient underwent a left thyroid nodule core biopsy with subsequent left thyroid hemithyroidectomy. The pathology stains of the excised left thyroid lobe core biopsy showed extra nodal zone lymphoma of mucosa- associated lymphoid tissue (MALT Lymphoma) with extensive plasmocytic differentiation. Surgical path confirmed extra nodal zone lymphoma of mucosa-associated lymphoid tissue (MALT Lymphoma) with extensive plasmocytic differentiation and foci of chronic lymphocytic thyroiditis. Immunochemistry studies supported a diagnosis of plasma cell neoplasm or the plasma cell component of a B-cell lymphoproliferative disorder. Short-term follow-up FDG-PET and CT imaging demonstrated post-surgical changes without evidence of recurrence. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.