Melanotic neuroectodermal tumor of infancy in thigh of an infant--a rare case report with diagnostic implications.

Melanotic neuroectodermal tumor of infancy (MNTI) is an uncommon tumor of neural crest origin, almost invariably identified in the head and neck region. It is a relatively benign tumor but can recur and rarely metastasize. Herein, a rare case of MNTI in the thigh of an infant is documented. Radiographic imaging showed a sclerotic and lytic lesion in the metadiaphyseal region of the right femur with a soft tissue component. The clinicoradiological impression was of a malignant round cell tumor and osteomyelitis. The patient's urinary vanil mandelic acid (VMA) level was elevated. FNAC smears revealed a tumor with round to polygonal cells, focally containing black melanin pigment. Biopsy and tumor excision revealed a tumor with cells in cords and nests embedded in a fibrocollagenous stroma and showed bone and soft tissue infiltration. On immunohistochemistry, tumor cells displayed immunoreactivity to vimentin, cytokeratin (CK), CK7, CK19, and MIC2, and focal reactivity for synaptophysin and HMB45. Diagnosis of an MNTI was made. The patient underwent induction chemotherapy with extracorporeal radiotherapy, followed by a soft tissue excision that revealed residual tumor. Surgically, free marrow margins were accomplished, and the patient is currently being followed-up. To the best of our knowledge this case is the fifth documented case in the English literature of MNTI in the thigh. The diagnostic and therapeutic implications are discussed.