Langerhans cell histiocytosis: another cause of a fluid-fluid level within an appendicular bony lesion.

We report a case of Langerhans cell histiocytosis (LCH) occurring in the pelvis of a 2-year 11-month-old female with fluid-fluid level seen on MRI. Aspiration of the fluid during biopsy showed it to be blood with a few inflammatory cells and eosinophils. Tissue obtained during the biopsy confirmed the diagnosis to be LCH.