胸腺瘤以甲狀腺外結節為表現：兩例個案報告

Thymoma Presenting with Extrathyroid Tumor Mimic Nodular Goiter: Report of Two Cases

胸腺腫瘤(thymic tumor)是相當少見的腫瘤，90%發生於前縱膈腔。異位胸腺瘤(ectopic thymoma)發生率極低，好發部位多樣性，若無重症肌無力特徵性臨床表現，診斷困難。本文報告2位案例因甲狀腺超音波檢查發現疑似甲狀腺外結節，頸部電腦斷層顯示為低顯影、均質、邊界清楚之腫瘤。腫瘤上端與左葉甲狀腺下方邊界相連，腫瘤與甲狀腺組織呈現不同的顯影程度。2位個案皆接受自頸部路徑之腫瘤切除手術，最後病理報告皆證實為胸腺瘤AB型。根據Masaoka staging system與世界衛生組織(World Health Organization, WHO)分類，診斷為第二期胸腺瘤(thymoma)，WHO type AB。臨床上若表現為前頸部腫塊，無明顯臨床症狀，無重症肌無力症的表徵，甲狀腺超音波等影像學檢查除考慮甲狀腺本身常見疾病外，還要考慮到異位胸腺瘤可能。

 

Thymic tumors are rare neoplasms that commonly arise in the anterior mediastinum. Ectopic thymoma is even rarer. Aberrant or remnant ectopic thymic tissue can occur anywhere along the entire thymic descent pathway during embryogenesis in the neck or whole mediastinum, rendering diagnosis highly difficult to make.

Herein we present 2 cases of ectopic thymoma presenting with an extra-thyroid nodule. Neck computed tomography (CT) revealed a hypodense and heterogeneous capsulated mass with smooth contour. The tumors were located in the anterior area of the neck and adjacent to the lower pole of the left side thyroid gland. These 2 cases both received anterior neck tumor excision. The mass was diagnosed as stage IIa and type AB thymoma based respectively on the Masaoka staging system and World Health Organization histological staging.

Although it is well known that thymoma is often associated with myasthenia gravis, ectopic thymoma is seldom presented with myasthenic symptoms. Moreover, ectopic thymoma located in the neck region is apt to be misdiagnosed as a thyroid mass or other infiltrative lesion. Ectopic cervical thymoma presents a diagnostic pitfall especially on a fine needle aspiration cytology. The favored treatment protocol of ectopic thymoma is surgical resection, including an adequate surgical margin from the tumor. It is important to be aware that cervical masses may be thymomas rather than thyroid masses.