Sonographic diagnosis of unifocal Langerhans cell histiocytosis of the skull.

The sonographic (US) findings of unifocal Langerhans cell histiocytosis of the occiput are described. The patient was a 3 year-old girl who presented with a painful soft tissue mass on the scalp. US demonstrated a large soft tissue mass with destruction of the underlying bone. The mass extended through the bony defect and consisted of a solid intracranial component and a predominantly cystic extracranial component. US is not usually associated with the diagnosis of Langerhans cell histiocytosis but in this case it provided valuable information that led to the primary differential diagnosis of Langerhans cell histiocytosis, which was confirmed by bone biopsy at surgery.