Lipofibromatosis of the knee in a 19-month-old child.

Lipofibromatosis is a rare benign fibrofatty tumor of childhood. The typical presentation of this tumor is as a poorly demarcated and slow-growing mass involving the subcutaneous or deep soft tissues. Lipofibromatosis was first described in 2000, and since then, a small number of cases have been reported in the literature. We report a case of a 19-month-old boy who presented with a swelling of the anterior aspect of the right knee since birth, which had increased in size out of proportion with his growth. Magnetic resonance imaging was extremely useful because it showed the lipomatous nature of the mass, narrowing the differential diagnosis to the pediatric fibrofatty soft tissue tumors. The histologic biopsy revealed the specific diagnosis of lipofibromatosis. We describe the radiologic and pathologic features of this entity and discuss the differential diagnosis in a young child with a fat-containing limb mass.