Diagnostic and Staging Evaluation

Germ cell tumors.

Lymphomas.

Stromal tumors.

Metastatic tumors.

Lung cancer.

Physical examination and history.

Chest x-ray. Approximately 50% of thymomas are diagnosed when they are localized within the thymic capsule and do not infiltrate surrounding tissues.[23]

Computed tomography (CT) scan. CT with intravenous contrast is useful in the diagnosis and clinical staging of thymoma. CT is usually accurate in predicting tumor size, location, and invasion into vessels, the pericardium, and the lungs.[27,28]The appearance of the tumor on CT may indicate the histological tumor type.[25] In a retrospective study involving 53 patients who underwent thymectomy for TETs, CT indicated that smooth contours with a round shape were most suggestive of type A thymomas, and irregular contours were most suggestive of thymic carcinomas. Calcification was suggestive of type B thymomas. In this study, however, CT was found to be of limited value in differentiating type AB, B1, B2, and B3 thymomas.[29]

Positron emission tomography (PET) scan. Fluorine F 18-fludeoxyglucose (18F-FDG) PET and thallium single-photon emission CT have been reported in small series for diagnosis and evaluation of therapeutic outcomes in thymic carcinoma.[30-33] Two small series reported that 18F-FDG uptake was related to the invasiveness of thymic carcinoma.[32,33] This raises the possibility of 18F-FDG PET use for diagnosis, treatment planning, and monitoring for recurrence. The impact of sensitivity and specificity on clinical therapeutic decisions is yet to be defined.

Magnetic resonance imaging (MRI). MRI can distinguish TETs from other malignant and benign mediastinal lesions. Chemical-shift MRI can help differentiate TETs from thymic hyperplasia and a normal thymus. Cardiac MRI is the preferred modality to evaluate for the presence of myocardial involvement. An MRI can help identify phrenic nerve involvement and is considered superior to CT for assessing chest wall invasion.[34]