前纵隔肿块-甲状腺诱发的假胸腺瘤：单纯胸腺增生

前纵隔肿块-甲状腺诱发的假胸腺瘤：单纯胸腺增生

Anterior mediastinal mass-thyroid-induced pseudo-thymoma: a pure thymic hyperplasia

引言：纵隔肿块包括广泛的组织病理疾病谱，其中三分之二是良性的。前纵隔肿块引起更多的关注，因为其中59%是恶性的，胸腺瘤是最常见的（1）。这些恶性肿块通常需要活检和手术治疗。真正的良性胸腺增生（TH）与Grave病（GD）的甲状腺毒症有关。抗甲状腺药物治疗后胸腺退化（2）以及胸腺肽水平与血清T4和T3之间的显著相关性（3）早有报道。然而，只有少数病例的这种共存的报告，这些假性胸腺瘤的管理仍然不清楚。

病例介绍：一名53岁女性，既往无明显病史，有3周劳力性呼吸困难加重史，伴有不适、心悸和严重震颤。就诊时心跳过速并伴有高血压。CTPA显示偶发孤立性前纵隔境界清楚软组织肿块。无钙化、邻近侵犯或纵隔淋巴结肿大。实验室显示TSH<0.01mIU/L，FT4>7.77ng/dL，总T3 625.4ng/dL。患者在医院开始服用类固醇、β受体阻滞剂和甲巯咪唑，并报告在接下来的几天内症状有所改善。由于被认为是甲状腺引起的胸腺增大，所以经肺病科会诊并推迟了有创手术。对患者进行CT随访，以评估甲亢治疗后肿块是否消退。

讨论：众所周知，与Grave病相关的TH发生在所有年龄组，最常见于与GD发病率相关的年轻人。许多早期的病例报告显示，在至少2-6个月的抗甲状腺药物治疗（4）、放射性碘治疗或甲状腺切除术后，随访CT显示胸腺肿块大小缩小。胸腺体积和密度也有所降低（5）。由于胸腺瘤，一些患者报告切除了GD相关的胸腺肿块，但最终组织病理学提示胸腺增生（4,5）。大量胸腺肿块（6,7）也与GD有关，抗甲状腺治疗后消退。影像学表现为良性，经组织病理证实为良性。

结论：我们在此报告一位老年女性GD，并意外发现前纵隔肿块。认为这是良性胸腺增生帮助我们免行活检和胸腺切除术。这些没有恶性特征的肿块在甲状腺功能亢进状态得到适当治疗后，可以通过复查CT监测其大小和一致性。在正常甲状腺状态6个月后胸腺体积缩小小于50%的情况下，应考虑进行MRI、活检或切除。

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.