Retroperitoneal lipoma in children: choosing among diagnostic imaging modalities.

We present two cases of benign retroperitoneal lipomas in children. Intravenous urography in both revealed large masses of fat density displacing the ipsilateral kidney superomediad. Angiography in one showed an avascular mass. The other patient had a markedly echogenic mass with indistinct margins on ultrasonography, and a computed tomographic scan confirmed the fatty composition of the tumor. Nineteen previously reported cases of retroperitoneal fatty neoplasms in children are reviewed. The urographic findings of a radiolucent mass displacing the ipsilateral kidney or ureter are highly specific for retroperitoneal lipoma and usually obviate the need for additional imaging procedures.