[Mediastinal space-occupying lesion of uncertain histology: difficulties of differential diagnosis]

A 78-year-old woman had, for the previous 4 months, been aware of an easily moveable tumour in the jugular region. She had been feeling well except for general fatigue. Physical examination revealed a mass in the jugular region, a little over 2 cm in diameter.

Routine laboratory tests were normal, except for a raised erythrocyte sedimentation rate. After ultrasound, scintigraphy and computed tomography, a biopsy was performed. Histologically it was suspicious of a centroblastic centrocytic non-Hodgkin lymphoma, but further pathological investigation established the diagnosis of a malignant thymoma.

The tumour was resected and histological examination confirmed a malignant thymoma with infiltration of surrounding tissues. Radiotherapy was subsequently undertaken.

Even though its evidence is low, a malignant thymoma or benign thymic tumour should be included in the differential diagnosis of a space-occupying mediastinal mass of unclear histology.