Neuroblastoma with a distinct organoid pattern: a clinicopathologic, immunohistochemical, and ultrastructural study.

We studied the organoid pattern in neuroblastoma, defined here as a characteristic histologic feature of the thin fibrovascular meshwork regularly surrounding the individual nests of neuroblastic cells. Among 75 neuroblastomas in our files, 11 cases were qualified as having the recognizable organoid pattern by hematoxylin-eosin stain morphology. The patients comprised five girls and six boys with ages at diagnosis ranging from 1 to 60 months (mean age, 14 months). Nine of the tumors were adrenal and two were retroperitoneal primary. The stages were I (four cases), III (two cases), IV (two cases), and IVS (two cases). All eight patients younger than 1 year are alive and well, whereas two of three patients older than 1 year died of disease. Immunohistochemical staining of those tumors having an organoid pattern showed a considerable number of S-100 protein-positive spindle cells present, mainly in the meshwork areas. Putative Schwann cells were identified ultrastructurally in five of the six tumors examined. In conclusion, organoid pattern in neuroblastoma is easily recognizable, is an indicator of good prognosis in younger children, and may well represent a close relationship between neuroblasts and putative Schwann cells.