RESIDENT CASE STUDIES

Week 5 May 19 - May 23, 2003: Case 1   

Table of Contents | List of Diagnoses | Case 1 | Case 2 | Case 3 | Case 4

One month old male with a maxillary lesion

Discussion:
Melanotic Neuroectodermal Tumor of  Infancy (MNTI) is a rare, usually benign and pigmented neoplasm of neural crest origin. Most cases occur in the maxilla of infants younger than 1 year old, usually with a male.

Melanotic Neuroectodermal Tumor of  Infancy (MNTI) is characterized by the biphasic cell population. The larger, polygonal cells have abundant eosinophilic cytoplasm, round to oval nuclei with prominent nucleoli. The larger cells tend to be in an alveolar or tubular arrangement surrounding the smaller cells. The large cells also contain granules, which are positive for melanin. The small cells are best characterized as small round blue cells. Necrosis, mitoses and pleomorphism are rare or absent. Ultrastructurally, the small cells have neurosecretory features, while the large cells demonstrate epithelial features.  

The differential diagnosis includes neuroblastoma, PNET, rhabdomyosarcoma and melanoma. However, melanotic neuroectodermal tumor of infancy is distinct in that it contains the biphasic population. While neuroblastoma and PNET are small round blue cell tumors, they do not contain the large, pigmented cell population. Rhabdomyosarcoma contains strap cells (pink bellies) and striations, which we also do not see in MNTI. Lastly, melanoma is included because of the pigment, however melanoma does not have a biphasic pattern or prominent cytokeratin positivity.

Most MNTIs are benign and respond to conservative excision. Histology is an unreliable means of predicting clinical behavior.

The large cells of MNTIs stain for CK, vimentin, S100, HMB45 and usually NSE (neuron specific enolase). The small cells stain for NSE, CD56 and occasionally Leu-7, but negative for cytokeratin and vimentin. Variable reactions are seen for synaptophysin (1).

References:

1. Barrett AW, Morgan M, Ramsay AD, et al. A clinicopathologic and immunohistochemical analysis of melanotic neuroectodermal tumor of infancy. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002 Jun;93(6):688-98. 

2. Jurincic-Winkler C, Metz KA, el al. Melanotic neuroectodermal tumor of infancy (MNTI) in the epididymis. A case report with immunohistological studies and special consideration of malignant features. Zentralbl Pathol 1994 Jul;140(2):181-5.