Infiltrating angiolipoma of the foot: magnetic resonance imaging features and review of the literature.

Angiolipoma is a benign soft tissue tumor with two subtypes: non-infiltrating and infiltrating. Although histologically benign, infiltrating angiolipoma can invade surrounding structures. The foot is a very rare location for angiolipoma, with only four cases reported in the English literature, including one infiltrating type. Here, we report a very rare case of infiltrating angiolipoma of the foot with magnetic resonance imaging (MRI) and ultrasonography (US) findings. A 7-year-old boy presented with a slowly growing foot mass. MRI showed an unencapsulated mass involving the third web space extending to the foot dorsum and sole. The mass was isointense to subcutaneous fat and was mixed with internal T1 low-signal-intensity enhancing areas. On US, we observed a heterogeneously hypoechoic mass with internal vascularity. Imaging and clinical features of angiolipoma and the radiologic differential diagnoses of a fat-containing mass in the pediatric foot are reviewed here. When there is an ill-defined foot mass with a fat component and variable enhancing portions in a child, infiltrating angiolipoma should be included in the differential diagnosis along with other fat-containing tumors.