Ectopic Thyroid in the Anterior Mediastinum Resected Through a Video-Assisted Transcervical Approach: Case Report

2019-07-03T16:08:22Z (GMT) by Carlos Henrique Boasquevisque

Introduction
The most frequent tumors in the anterior mediastinum are thymomas/thymic lesions (40%), lymphomas (25%), and germ cell tumors (20%). Substernal or retrosternal goiters/ectopic thyroid comprise 15% of anterior mediastinal masses (1).


Ectopic thyroid is a rare entity with an estimated prevalence of 1:100,000-300,000 (2) and 1:4,000-8,000 in patients with thyroid diseases (2). Ectopic thyroid tissue (ETT) can coexist with an orthotopic thyroid, although in the majority of the cases it is the sole existing thyroid tissue (1). Lingual thyroid is the most frequent type, corresponding to 47% to 90% of the reported cases (3, 4). ETT in the mediastinum comprises 1% of all cases (3, 5). In autopsy series, its incidence is reported to be 7% to 10% (5). Thullier and colleagues, in 2012, mentioned that only 7 cases had been described in the literature during the previous 30 years (4).
Surgical approaches used for resection of mediastinal ETT are median sternotomy, posterolateral thoracotomy, video thoracoscopy, robotic surgery, and transcervical and subxiphoid approaches. Localization in the mediastinum and size are important features to decide the surgical approach.
Herein, the authors report a case of an ectopic thyroid in the anterior mediastinum—initially judged to be a small thymoma—that was resected through a video-assisted transcervical approach.

Case Report
A 58-year-old woman sought medical treatment because of abdominal pain. Previously, she had been diagnosed with colonic diverticular disease. At the emergency department, an abdominal computed tomography (CT) was performed and no abdominal abnormality was seen. A 6 mm pulmonary nodule was detected in the left inferior lobe and a follow-up chest CT revealed an anterior mediastinum density below the level of the aortic arch, measuring 24 x 12 mm and showing high contrast enhancement (Figure 1). Lymphadenopathy, thymoma, ectopic thyroid, and parathyroid adenoma were the diagnostic hypotheses in the radiology department.


The patient was aware of bearing a nontoxic multinodular goiter and had sought consultation with two head and neck surgeons. Thyroid hormones levels were in the normal range (TSH: 1.29 mcUI/ml, normal range: 0.4-4.3 mcUI/ml; free T4: 1.0 ng/dl, normal range: 0.7-1.9 ng/dl). Thyroid ultrasound with Doppler showed a multinodular goiter with no signs of malignancy. One nodule in the right lobe underwent fine needle aspiration and was benign (Class II, Bethesda). Thyroid surgery was not considered by the two consulting surgeons at that time.


The patient reported muscle weakness, but myasthenia gravis was not present. Anti-acetylcholine receptor antibody detection was negative (0.23 nmmol/L; reference: negative < 0.45 nmol/L, positive > 0.45 nmol/L). Electroneuromyography was also negative for myasthenia gravis. Thyroid scintigraphy was not performed, as the patient had undergone CT scan with iodine contrast and nuclear imaging could not be done for at least four weeks. In addition, the main consideration was a small thymoma, and surgery for diagnosis and treatment had been decided.
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