Rhabdomyosarcomas in the head and neck: MR imaging evaluation. To determine the typical magnetic resonance (MR) signal intensity characteristics of rhabdomyosarcomas, short repetition time (TR)/short echo time (TE) (T1-weighted) and long TR (proton density and T2-weighted) images of 13 patients with rhabdomyosarcomas of the head and neck were retrospectively reviewed. Seven patients received gadopentetate dimeglumine injections. The most common MR appearance was that of a homogeneous mass, hyperintense to both muscle and fat on long TR/long TE images and isointense or minimally hyperintense to muscle on short TR/short TE images. All lesions of the patients who received gadopentetate dimeglumine enhanced markedly. Two lesions had intratumoral hemorrhage, and six were markedly heterogeneous in signal intensity. Similar MR signal intensity patterns have been described for lymphomas and nasopharyngeal carcinomas. The forte of MR imaging lies in its ability to delineate precisely the extent of the rhabdomyosarcoma. 