Unusual ultrastructural findings in neuroblastoma.

A morphologic study was made of the cell population which had infiltrated the bone marrow of a five-year-old boy. These cells showed a tendency to form rosette-like structures. These structures as well as the presence (at ultrastructural level) of neurosecretory granules, cell processes, and microtubules in the neoplastic cells led to a diagnosis of neuroblastoma. Certain characteristics, not previously reported in neuroblastoma, were identified, such as gap junction type intercellular contacts, paracrystalline arrays in mitochondrial atpyical cristae and nucleolus-like bodies (nematosomes). Gap junctions are involved in the intercellular transfer of ions and low molecular weight metabolites and may explain the tendency to form cellular cluster in "rosettes" which are characteristic of this neoplasm. The presence of nematosomes in the tumor cell cytoplasm is one more piece of evidence which substantiates the nervous origin of these cells.