<prompt> A young child with backache reveals a solitary collapsed dorsal vertebra with preserved intervertebral disk spaces and no evidence of soft tissue mass. The most likely diagnosis is?LymphomaLangerhanss cell histiocytosisEwings sarcomaMetastases  <response>: Ans BThis classic imaging appearance is called Vertebra plana and in children is most commonly seen in Langerhanss cell histiocytosis 