Ectomesenchymoma is defined as a rhadomyosarcoma with a neural or neuronal component. It is rare, usually affect children aged <5 years and paratesticular region is one of the most common sites of involvement. The rhadomyosarcoma component is usually of embryonal or spindle cell type. Neuronal or neural differentiation includes ganglion cells, ganglioneuroma, neuroblastoma or malignant peripheral nerve sheath tumor. Treatment is based on protocols for rhaddomyosarcoma and the treatment responses are similar to those of pure rhabdomyosarcoma. Factors for good prognosis include size < 10 cm, low stage, superficial location and absence of alveolar rhabdomyosarcoma.
AFletcher CDM, Bridge JA, Hogendoorn PCW, Mertens F. WHO Classification of Tumours of Soft Tissue and Bone. International Agency of Research on Cancer, 4th edition, 2013. Pg. 191.