Metastatic Ectopic Thymoma of the Neck without Mediastinal Involvement

Thymoma is a rare malignancy with usual location in the antero-superior mediastinum. Occurrence of an extra-mediastinal thymic malignancy in the neck with lung metastasis and without involvement of the mediastinum is an extremely rare condition. Staging systems and treatment guidelines are defined for mediastinal thymomas but not for ectopically located thymomas.

38-year-old female presented with the chief complaint of a progressive neck swelling, located predominantly in the right lateral neck, extending to the midline. Computed Tomography showed a heterogenous peripherally enhancing mass with likely origin from the thyroid gland. The mass measured 12 x 6 x 3.5 cm in size and extended from the hyoid bone superiorly to the suprasternal location inferiorly. Additionally, there were multiple, variable sized subpleural nodules scattered in both lungs, suggestive of lung metastases. Histopathology and immunohistochemistry findings from neck mass confirmed the diagnosis of Thymoma Type A. 

Thymoma is a rare tumor that typically does not show aggressive behaviour. Extra-mediastinal neck thymoma with bilateral lung metastasis is an extremely rare presentation. Thymoma presenting as neck swelling without mediastinal extension on radiology, poses a diagnostic dilemma. Histopathology with immunohistochemistry helps to confirm the final diagnosis. Surgery is the mainstay for the management of localized tumors with adjuvant treatment reserved for incompletely resected tumors or advanced stage. Systemic metastasis are rare in this indolent tumor and chemotherapy regimens are investigational. Clinical presentation, prognostic factors, staging and management guidelines are still not well defined for this rare tumor with atypical location.