Melanotic neuroectodermal tumor of infancy (MNTI) is a rare pigmented tumor that primarily affects the calvaria or facial skeleton of children, typically during infancy. It is usually a benign tumor, albeit locally aggressive.
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Epidemiology
Most cases are diagnosed during infancy, usually within the first 6 months of life 1,2. No convincing sex predilection has been reported 1,2.
Clinical presentation
The vast majority of cases are craniofacial with more than two thirds of reported cases involve the maxilla 1,2. Clinical presentation is usually with a rapidly growing mass, only sometimes obviously melanotic 1,2. In some instances the mass results in displacement of teeth and distortion of the nasal and oral cavities, in turn resulting in feeding difficulties 1.
Pathology
Macroscopic appearance
Blue-black discolouration of the tumor occurs secondary to melanin pigment produced by the tumor.
Microscopic appearance
Non-encapsulated mass composed of abundant large epithelioid cells that contain melanin. They are usually arranged in alveolar or tubular formations around clusters of small neuroblastic cells 1.
These tumors are thought to be of neural crest origin 1,2.
Radiographic features
Melanotic neuroectodermal tumor of infancy require multimodality imaging, with MR and CT being complementary.
Soft tissue invasion and tumor margins are best evaluated with MR imaging, while CT is best for evaluating bone involvement.
Plain radiograph
Radiographs of the facial skeleton are non-specific demonstrating a lucent lesion often with irregular bony changes 2.
CT
On CT these lesions appear as well-demarcated lesions, often with hyperostosis of adjacent bone 1.
They are typically of homogeneous hyperdense soft tissue masses with uniform enhancement post contrast administration 1,2.
MRI
MRI signal is in keeping with melanocytic histology 1,2.
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T1
- may be heterogeneous in signal
- usually areas of intrinsic hyperintensity
- T2: hyperintense to muscle
- T1 C+ (Gd): enhancement is usually present but can be difficult to assess if very T1 hyperintense
Treatment and prognosis
Surgical excision is treatment of choice, and it is usually curative although recurrences are not uncommon, encountered in approximately 15% of cases within the first 12 months 2.
Treatment options include adjuvant and neoadjuvant therapies. Chemotherapy in cases of multiple aggressive recurrences and/or inoperable tumors.
Radiotherapy is rarely used in combination with surgical therapy or chemotherapy.
Although usually considered a locally aggressive benign tumor, malignant variants have been reported in around 2-6% of cases 1. Distant metastatic spread is uncommon, encountered only in 3% of cases 1.
History and etymology
This tumor was first described in 1918 3. In 1966, Borello and Gorlin proposed the term melanotic neuroectodermal tumor of infancy after reporting a case with high urinary vanillymandelic acid, suggesting a neural crest origin 2.
Differential diagnosis
The differential, once CT and MRI has been obtained, largely that of other soft tissue tumors or tumor-like masses, including 1:
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