Soft tissue aneurysmal bone cyst in a 10-year-old girl.

We report the case of a 10-year-old girl with a soft tissue aneurysmal bone cyst (STABC) located in the posterior aspect of the left shoulder. Conventional radiography revealed an oblong mass with a calcified rim. On the computed tomography scan, the lesion appeared to have a non-uniform intralesional density with an incomplete rim. Magnetic resonance imaging revealed a multi-cavity lesion with fluid-fluid levels. Following pathological examination, the lesion was diagnosed as a STABC. This may be only the twentieth reported case in the English literature of this extremely rare benign tumor occurring in soft tissue. Eight months after surgery the patient was assessed at our outpatient clinic and found to have excellent mobility of her left shoulder and no sign of recurrence.