Melanotic Neuroectodermal Tumor of Infancy Occurring in the Left Thigh of a 6-Month-Old Female Infant

Abstract

We report an exceptional case of melanotic neuroectodermal tumor of infancy (MNTI) occurring in the soft tissue of the left thigh of a 6-month-old female infant. The tumor consisted mainly of small round cells (neuroblasts) arranged in cords and nests that were separated by broad fibrovascular areas. In addition, there were a few medium-sized tumor cells containing melanin pigment (melanocytic cells) that in electron microscopy contained melanosomes as well as tonofilaments. Both tumor cell types immunostained for neuron-specific enolase (NSE) and vimentin, and the melanocytic cells reacted additionally with the antikeratin antibody KL1. Within the tumor stroma, neurofilament- and S-100-protein-positive neural cells and vimentin- and desmin-positive myofibroblasts were seen. Although dense-core granules were demonstrated ultrastructurally in some neuroblasts, no immunostaining for chromogranin A, Leu-7, serotonin, or regulatory peptides was found. MNTI located in an extremity can be confused with malignant small round and blue cell tumors of childhood. The distinction between MNTI and these tumors is of clinical significance because MNTI, in most cases, is a benign tumor that, in contrast to the latter, can be cured by complete excision. The presence of a biphasic cell population with neuroblasts and melanocytic cells must be considered the main diagnostic feature of MNTI.

Neurogenic Tumors of Soft Tissue

“…Scattered isolated strands or pseudoglandular formations of pigmented epithelial cells or clusters of small cells may also be seen within the intratumoral stroma [545,552]. There may be significant variation in the degree of pigment generation, and sometimes melanin can be seen within the small cell component [542,548].…”

“…Although both cell types are immunoreactive for vimentin and neuron-specific enolase, they otherwise show different immunophenotypes. Whereas the large cells are also positive for cytokeratins and certain melanocytic markers (HMB45 and dopamine beta-hydroxylase), the small cell component is not [542,545,546,552]. S-100 protein expression is usually negative in both components, with focal expression observed in less than 10% of cases [542,545,546,552].…”

“…Currently, there are no unequivocal clinical or pathologic features predictive of malignancy [545,547,550,552]. Nevertheless, some investigators have suggested that extramaxillary tumors may be more aggressive [547,566].…”

Melanotic Neuroectodermal Tumor of Infancy in the Epididymis

“…In 1971, the World Health Organization designated this neo plasm 'melanotic neuroectodermal tumor of infancy' [26], While the genesis of MNTI is uncertain, several investiga tors found evidence of a neuroectodermal (neural crest) origin by biochemical, histochemical, ultrastructural and immunohistochemical analyses [1][2][3][4][5][6][7][8][9][10][11][12]. Proliferating cells in MNTI have unique and peculiar morphological charac teristics of neuroectodermal differentiation, making the precise identification of this disease possible by morpho logical study.…”

“…A neural crest origin has been suggested by the published histochemical, ultrastruc tural and immunohistochemical studies [1][2][3][4][5][6][7][8][9][10][11][12], Since its first description by Krompechcr [13] in 1918, about 200 cases of MNTI have been published. This tumor usually affects the lower parts of the face and skull, particularly the maxilla, although it has also originated in other sites, including the epididymis [6][7][8][9][10][11][12][14][15][16][17][18][19][20][21][22][23][24][25], thigh [4], femur [3], and foot [5]. The 4-month-old boy described here represents the 23rd reported case of MNTI involving the epididymis.…”