What is thymic rebound?

Question

Would appreciate a response from a radiologist or oncologist if one happens to read this ... I have a history of Hodgkin's Disease with extensive chest involvement. I am now 10 months out of treatment. Treatment was 8 cycles of ABVD chemo, no radiation. I had a PET scan that showed a new finding of a "somewhat triangular concave edged" soft tissue mass with moderate uptake (SUV 3.0 to 3.5) located in the anterior mediastinum. The radiologist noted that this "may represent thymic rebound." I have a lot of scar tissue in my chest, but all those areas were hypometabolic.

I'm not too concerned, because my oncologist said he'd simply continue following up with three month scans as usual. I also have no clinical signs of disease.

But I'm curious -- I've done a little research and still don't quite understand what this is. What is thymic rebound? Is it common in adults? (I'm in my late 20s.) Does it require treatment? Why does it happen and most importantly is it bad (i.e. a precursor to relapse)? Other than a biopsy (which I assume my oncologist isn't interested in right now as he said he'd just follow up as usual), is there any way to know if this any imaging study to show that this is more likely thymic rebound versus a relapse?

Answer 1

The thymus is a lymphoid organ in the anterior mediastinum. In general as you get older, it gets smaller. With chemotherapy or radiotherapy, the thymus shrinks. This is normal. After chemotherapy or radiation therapy, the normal thymus recovers. As it does so, sometimes its even larger than normal for a while. It can show up on CT scan and on PET or PET CT scan. This is normal, healthy, sign of recovery. The only danger is when the changes in the scan are misinterpreted as relapse. Your oncologist told you just the right answer. It sounds like you are in good hands.