Electron microscopy in the diagnosis of neuroblastoma.

I review the accumulated knowledge regarding the electron microscopy of neuroblastic tumors using a retrospective study of 13 primarily small cell neoplasms for which the diagnosis of a neuroblastic tumor (neuroblastoma, ganglioneuroblastoma, ganglioneuroma) was either considered or eventually established. A fine fibrillary background, even if focally distributed by light microscopy and seemingly not recovered in the thick sections, correlated with the presence ultrastructurally of neuritic processes bearing dense core ("neurosecretory") granules and lucent vesicles. In three cases without any fibrillary background by light microscopy, granule-bearing processes were not found by electron microscopy, and different diagnoses were subsequently established for two of those cases. From the standpoint of diagnosis, the sampling error normally introduced in ultrastructural examinations has not been reported to be a significant problem, nor was it in the present cases. Therefore, in supporting a light microscopic diagnosis of neuroblastoma, neuritic processes containing dense granules with or without lucent vesicles should be documented. Neuroblastic tumors with evidence of maturity, ie, ganglion cell differentiation, had the best developed morphologic features by both forms of microscopy. Schwann cells were observed in four cases, including one neuroblastoma. The presence of these cells by electron microscopy, although absent by light microscopy, may reflect an early phase of tumor maturation.