Flip-flop effect

The so-called flip-flop effect refers to a confusing MRI appearance of the skeletal system and subcutaneous tissues. It is seen in a variety of severe fat depletion conditions responsible for diffuse bone marrow serous atrophy and modification or loss of the subcutaneous fat.

Not to be confused with the potential flip-flop appearance of the liver on contrast-enhanced CT in Budd-Chiari syndrome.

Pathology

Diffuse serous atrophy of the bone marrow occurs in a variety of medical conditions (mainly anorexia nervosa and severe cachexia), where, due to hormonal and cellular depletion/imbalance , marrow fat will be replaced by watery substance and extracellular fluid .

Radiographic features

This phenomenon will increase T1 and T2 relaxation times leading to confusing MRI findings. Intermediate to low bone marrow and soft tissue signal will be seen on T1 weighted images while corresponding high signal intensity of these compartments will be found on fat-suppressed fluid sensitive sequences (T2 Fat Sat and STIR).

These confusing MRI findings can be confirmed by spectroscopic analysis or Dixon technique, confirming fat depletion and water predominance to avoid misinterpreting these images as a technical problem, with ensuing unnecessary repetition on the MR study .

Diagnostic considerations

See under the pathology section in the bone marrow serous atrophy article.