Melanotic neuroectodermal tumor of infancy: an ultrastructural study, literature review, and reevaluation.

Two cases of melanotic neuroectodermal tumor of infancy were examined by electron microscopy and an extensive review of the literature was performed. Ultrastructural examination revealed several features not previously described for this lesion. Three different types of melanin granule formation were observed, many cells had a single cilium, and cell junctions of the "close" or "modified-tight" type were seen, but no desmosomes were found. The morphologic data were consistent with the concept that the tumor arises from neural crest cells. The review of the literature indicated that there have been 158 reported cases of this lesion, including the two reported here. There were five cases of malignant tumor reported for a rate of 3.2%. This rate of malignancy is very high in view of the fact that the tumor has been described as universally benign. The significance of this finding is discussed with regard to melanin-producing lesions of the oral cavity.