The “Flip-Flop Phenomenon”: Treated Osseous Metastases & Reactive Marrow Uptake

When scattered areas of intense FDG uptake are noted within multiple vertebral bodies, the appearance usually indicates malignancy (typically metastatic disease or lymphoma). 

If, however, intense uptake within multiple vertebral bodies is noted after chemotherapy (especially if colony stimulating factors were administered), careful attention must be made to assure that the areas of increased uptake do not simply correspond to normal reactive marrow interspersed among regions of non-avid treated metastatic disease – the so-called “flip-flop phenomenon”.

When the treated lesions are sclerotic, the “flip-flop phenomenon” is relatively easy to notice. When lesions are subtle and non-sclerotic after treatment, this phenomenon can be more easily overlooked.

These cases of “flip-flop phenomena” indicate successful treatment, with “no evidence of active malignancy.”