Thallium-201 scintigraphy for assessment of a gallium-67-avid mediastinal mass following therapy for Hodgkin's disease.

Differentiating thymic rebound from recurrent tumor may be difficult in pediatric patients following chemotherapy for Hodgkin's disease. We present a patient who had both a negative 67Ga scan and computed tomography (CT) of the chest at diagnosis and demonstrated gallium avidity and CT evidence of a new mediastinal mass at the completion of chemotherapy. There was, however, no other clinical or laboratory evidence of disease recurrence. Thallium-201 imaging was subsequently performed and demonstrated no significant radionuclide accumulation within this anterior mediastinal mass. CT shows only the presence of a mass, but not it's nature. Gallium-67 scintigraphy, while used widely as an indicator of tumor viability, may demonstrate increased uptake in cases of thymic rebound. Thallium-201 imaging has previously been shown to demonstrate increased uptake in mediastinal malignancy. Conversely, no significant mediastinal uptake of 201Tl, as in this case, provides additional supportive evidence for a benign mediastinal entity such as thymic rebound.