Atypical malignant round cell tumour of the femur.

We report an atypical case of malignant round cell tumour in a 25-year-old man who presented with pain in the left hip of insidious onset and long duration of about 1½ years. Radiologically, the tumour was meta-epiphyseal in location with sparing of the diaphysis and showed a defined, narrow zone of transition. These appearances are contradictory to the well documented classical features of malignant round cell tumours, which usually present with a short history, are meta-diaphyseal in location, and appear ill-defined with a wide zone of transition due to infiltration of the adjacent bone.