Cells have dark, dusty blue nuclear chromatin and minimal cytoplasm ("small round blue cell" tumor) (image C).
Vaguely nodular growth pattern.
Homer-Wright rosettes a characteristic feature (seen in only 30%) which consist of a ring-like arrangement of neoplastic cells with a central area of pink neuritic process. No central lumen in the rosettes (image D).
Maturation is evidenced by ganglionic differentiation (more eosinophilic cytoplasm, large eccentric nucleus with prominent nucleolus [owl's eye]).
Poorly differentiated if <5% ganglion differentiation.
Immunohistochemistry: NB84+, neurofilament+, chromogranin+ and synaptophysin+.
Prognosis depends on multiple variable (age, histologic features, stage, as well as some molecular (MYCN, DNA ploidy) and genetic (Ch3 1p36, Ch 17q gain).
Can metastasize by lymphatics or blood, and commonly to skeletal system especially skull and orbit (Hutchinson's syndrome) and to liver (Pepper's syndrome).
DDX: other pediatric small round blue cell tumor such as Ewing sarcoma/primitive neuroectodermal tumor (PNET) (CD99+), rhabdomyosarcoma (desmin+), Wilms' tumor (WT1+) and lymphoma (CD45+).