Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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June 27, 2024
Melanotic Neurectodermal Tumor of Infancy
- Background:
- Melanotic neuroectodermal tumor of infancy (MNTI) is a rare neoplasm, usually considered benign, but showing a rapid growth rate and local aggressiveness. There is a potential for local recurrence in approximately 15% of cases, with distant metastasis being rare.
- Clinical Presentation:
- This tumor occurs in the maxilla in more than two-thirds of cases, but also occurs in other parts of the skull and can rarely occur in CNS structures. It usually presents in infants younger than 1 year of age as a painless, solitary, and rapid-growing pigmented swelling, with facial disfigurement in large lesions. Occasionally, the neoplasm is visible at birth, but most often it is discovered by the parents during the first few months of life.
- Key Diagnostic Features:
- Although definite diagnosis is histologic, imaging plays a key role in the diagnostic work-up, with MR and CT being useful.
- CT shows a predominantly lytic and expansile bone lesion with a prominent extra-osseous soft tissue component. Extensive hyperostosis and soft-tissue osteogenesis may occur, and bony spicules perpendicular to the vault can be present, giving a sunburst appearance. The soft tissue component is usually homogeneous and isointense to muscle, but can be heterogeneous.
- Tumor margins are seen particularly well on MRI, and the lesions are usually well-demarcated. The soft tissue component of MNTI is commonly described as being iso-hypointense on T1-weighted and slightly hyperintense to muscle on T2-weighted images, and areas of intrinsic hyperintensity can be present both on T1 and T2.
- There is usually marked contrast enhancement in all non-ossified components.
- On angiographic studies, vessel displacement caused by tumor mass is seen, as well as a vascular homogeneous tumor stain persisting into the venous phase.
- Differential Diagnosis:
- Small round blue cell tumors: these include rhabdomyosarcoma, Ewing sarcoma and neuroblastoma. They can be hard to distinguish from MNTI on imaging alone, as they can have similar morphological and signal characteristics, including the spiculated bony reaction, but tend to show less enhancement compared to MNTI.
- Intraosseous proliferating hemangioma: a small MNTI centered in the bone with a sun-burst appearance may mimic an intraosseous hemangioma, but the latter usually doesn’t show extra-osseous soft-tissue components nor rapid growth.
- Dentigerous cyst: there are descriptions of small lesions located in the pre-maxilla and enclosing a tooth, which can be mistaken for a dentigerous cyst, although on MRI the lesion shows cyst-like signal characteristics, with no solid component nor enhancement.
- Treatment:
- When feasible, complete excision is the best treatment, though local recurrence rates are not negligible.
- On larger lesions, neoadjuvant chemotherapy or chemotherapy alone may be used. Chemotherapeutic agents used to treat MNTI are based on the treatment protocols for neuroblastoma.
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