ANTERIOR MEDIASTINAL MASS-THYROID-INDUCED PSEUDO-THYMOMA: A PURE THYMIC HYPERPLASIA

Abstract

SESSION TITLE: Medical Student/Resident Disorders of the Mediastinum Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: October 18-21, 2020 INTRODUCTION: Mediastinal masses encompass a broad spectrum of histopathology among which two-thirds are benign. Anterior mediastinal masses draw more attention because 59% of them are malignant, thymoma being the most common(1). These malignant masses more often warrant biopsy and surgical intervention. True benign thymic hyperplasia (TH) is associated with thyrotoxicosis in Grave’s disease (GD). Involution of thymus after treatment with anti-thyroid drugs(2) and significant correlation between thymulin levels with Serum T4 and T3 have been reported earlier(3). However, there are only a few cases of this coexistence that are reported and management of these pseudo thymomas is still unclear to many. CASE PRESENTATION: A 53-year-old female with no significant past medical history presented with 3-week history of worsening exertional dyspnea associated with malaise, palpitations, and severe tremors. She was tachycardic and hypertensive on arrival. CTPA revealed an incidental non-discrete well-defined anterior mediastinal soft tissue mass. There were no calcifications, adjacent invasion or mediastinal lymphadenopathy noted. Labs showed a TSH < 0.01 mIU/L, FT4 > 7.77 ng/dL and total T3 625.4 ng/dL. Patient was started on steroids, betablockers and methimazole in the hospital and reported symptom improvement in the next few days. Pulmonology was consulted and invasive procedure was deferred since it was thought to be thyroid induced thymic enlargement. Patient was set up with follow up CT to assess for regression of the mass with treatment of hyperthyroidism. DISCUSSION: TH associated with Grave’s disease is known to occur in all age groups, most commonly in young adults correlating with GD incidence in the age group. Many of these earlier case reports revealed regression of the thymic mass size on follow-up CT after at least 2-6 months of anti-thyroid treatment with medications (4), radioactive iodine therapy or thyroidectomy. Decrease in thymic volume and density were also noted (5). Due to concerns of thymoma, some patients had reported resection of GD associated thymic mass but eventually histopathology suggested thymic hyperplasia(4,5). Massive thymic masses (6,7) were also associated with GD, that regressed with antithyroid treatment. Radiological features of these masses suggested benign appearance and later proved to be TH by histopathological diagnosis. CONCLUSIONS: We here present an older adult female with GD and incidentally found anterior mediastinal mass. Considering this as benign thymic hyperplasia helped us prevent biopsy and thymectomy. These masses with no malignant features can safely be monitored for size and consistency by serial CT following appropriate treatment of hyperthyroid state. An MRI, biopsy or resection is considered in cases when there is less than 50% regression in thymic volume after 6 months of euthyroid state. Reference #1: 1. Almeida PT, Heller D. Anterior Mediastinal Mass. In Treasure Island (FL); 2020. Reference #2: 4. Dalla Costa M, Mangano FA, Betterle C. Thymic hyperplasia in patients with Graves’ disease. J Endocrinol Invest 2014;37(12):1175–9 Reference #3: 5. Haider U, Richards P. Thymic Hyperplasia Associated with Graves ’ Disease: Pathophysiology and Proposed Management Algorithm. 2017;27(8):994–1000. DISCLOSURES: No relevant relationships by Dani Fribourg, source=Web Response No relevant relationships by Rathnavali Katragadda, source=Web Response