The thymus will undergoing hyperplasia following systemic chemotherapy. This proliferation may be detected on a follow-up positron emission tomography (PET) scan. This can result in the patient undergoing unnecessary surgery.


Imaging study: PET scan use 19-fluoro-2-deoxyglucose (FDG)


Clinical findings:

(1) A patient who has recently undergone therapy for a malignant neoplasm.

(2) A PET scan shows uptake in the mediastinum.

(3) It is decided to take the patient to biopsy rather than wait to see if the signals stabilized or decline.

(4) Biopsy shows only regenerating thymus without residual tumor.


The problem is particularly important in Hodgkin's disease or other tumors involving in the mediastinum.


This can be avoided by:

(1) being aware of the possibility

(2) waiting a period of time before doing a PET scan

(3) being willing to monitor the change in size with time. It may take a year for the thymus to normalize but it will stabilize and start to decrease sooner than that..


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