Macroscopic Usually there is a smooth, firm mass, with mottled white-gray to blue-black cut surfaces. The overall size ranges from 1–10 cm with a mean size 3.5 cm. Microscopic The tumor is usually very well circumscribed but not encapsulated. There are two cell types present (biphasic), arranged in alveolar or tubular configurations.A high power of<unk>  showing pigmented large epithelioid cells and smaller primitive cells (hematoxylin and eosin stain). There are centrally located, small, darkly staining cells comprising the majority of cells. These cells have a fibrillary cytoplasm surrounding round nuclei with coarse and heavy nuclear chromatin. These cells are surrounded by much larger polygonal cells that have open nuclear chromatin and abundant opaque cytoplasm that has granular melanin pigment.A high power of<unk>  showing pigmented large epithelioid cells and smaller primitive cells in alveolar nests (hematoxylin and eosin stain). There is usually no hemorrhage, necrosis or increased mitoses. Immunohistochemistry The lesional cells will show cross reactivity with several different families of immunohistochemistry markers (polyphenotypic), including neural, melanocytic, and epithelial. * Large tumor cells: Keratin, vimentin, HMB-45, NSE, CD57 * Small tumor cells: Synaptophysin, GFAP, NSE, CD57 * There is usually a variable expression of EMA and S100 protein. Differential diagnoses It is important in this age group to exclude other tumors that can have a similar appearance, such as rhabdomyosarcoma, lymphoma, Ewing sarcoma (primitive neuroectodermal tumor), or even a melanoma (although they are very very rare in infants).
Melanotic neuroectodermal tumor of infancy
Infantile hemangiopericytoma
Primitive neuroectodermal tumor
Neuroma cutis
Pediatric ependymoma
Retinoblastoma
Neurothekeoma
Ameloblastoma