Melanotic schwannoma mimicking metastatic pigmented melanoma: a pitfall in cytological diagnosis

Nerve-associated Schwann cell precursors contribute extracutaneous melanocytes to the heart, inner ear, supraorbital locations and brain meninges

Melanocytes are pigmented cells residing mostly in the skin and hair follicles of vertebrates, where they contribute to colouration and protection against UV-B radiation. However, the spectrum of their functions reaches far beyond that. For instance, these pigment-producing cells are found inside the inner ear, where they contribute to the hearing function, and in the heart, where they are involved in the electrical conductivity and support the stiffness of cardiac valves. The embryonic origin of such extracutaneous melanocytes is not clear. We took advantage of lineage-tracing experiments combined with 3D visualizations and gene knockout strategies to address this long-standing question. We revealed that Schwann cell precursors are recruited from the local innervation during embryonic development and give rise to extracutaneous melanocytes in the heart, brain meninges, inner ear, and other locations. In embryos with a knockout of the EdnrB receptor, a condition imitating Waardenburg syndrome, we observed only nerve-associated melanoblasts, which failed to detach from the nerves and to enter the inner ear. Finally, we looked into the evolutionary aspects of extracutaneous melanocytes and found that pigment cells are associated mainly with nerves and blood vessels in amphibians and fish. This new knowledge of the nerve-dependent origin of extracutaneous pigment cells might be directly relevant to the formation of extracutaneous melanoma in humans.

What Tactics Should a Surgeon Choose to Treat a Black Extracerebral Tumor? A Case Report of Psammomatous Melanotic Schwannoma of the Meckel Cave and Literature Review

BACKGROUND

Neoplasms located in the Meckel cave account for 0.2%-0.5% of all intracranial tumors. This area is the site of many types of pathologic lesions, most often trigeminal nerve schwannomas and meningiomas. Melanin-containing tumors are rare in this area. These tumor types can be suspected if the magnetic resonance characteristics of a tumor has some differences in comparison with other types of central nervous system neoplasms. In fact, differential diagnosis of melanotic tumors is based mainly on the histopathologic criteria and immunohistochemical profile. This article presents a case report of melanotic schwannoma of the Meckel cave and a literature review of the problem.

CASE DESCRIPTION

A 23-year-old man underwent a 2-stage surgery for a dumbbell pigmented mass lesion located in the Meckel cave. No signs of recurrence were seen on follow-up magnetic resonance imaging (MRI) 3.5 years after the operation.

CONCLUSIONS

Melanin-containing tumor can be suspected in the presence of radiologic characteristics, such as a hyperintense MRI signal on T1-weighted images and a hypointense signal on T2-weighted images. If a black extracerebral tumor is detected, the main course of surgical treatment is maximal excision despite it possibly being a malignant melanoma and the temptation to perform partial resection because of an unfavorable prognosis. Chemotherapy can be justified in the presence of an aggressive melanotic schwannoma.

Fatal Carney Complex in Siblings Due to De Novo Large Gene Deletion

CONTEXT

Carney complex (CNC) is a rare multiple neoplasia syndrome involving cardiac, endocrine, neural, and cutaneous tumors and a variety of pigmented skin lesions. CNC can be inherited as an autosomal dominant trait, but in about one-third of patients, the disease is caused by de novo mutation in the PRKAR1A gene localized on chromosome 17q22-24. Most of the mutations include single base substitutions and small deletions/insertions not exceeding 15 base pairs. Recently, large germline PRKAR1A deletions have been described and may cause a more severe phenotype.

CASE DESCRIPTION

Herein, we report the cases of two siblings with CNC with a de novo large deletion of 107 kb at 17q24.2 associated with acromegaly in both and primary pigmented nodular adrenocortical disease, cardiac myxoma, and lethal metastatic melanotic schwannian tumor at the age of 27 years in one of them, supporting the hypothesis that large deletions of PRKAR1A lead to severe disease.

CONCLUSIONS

To our knowledge, this is the first description of familial CNC in siblings in which neither parent carried the deletion in blood-derived DNA, suggesting that one of them had germ cell mosaicism for this deletion. Testing for large gene deletions should be obtained in all patients who meet the diagnostic criteria for CNC but do not have a PRKAR1A mutation by Sanger sequencing.

Pigmented Lesions of the Nervous System and the Neural Crest: Lessons From Embryology

Neurosurgeons encounter a number of pigmented tumors of the central nervous system in a variety of locations, including primary central nervous system melanoma, blue nevus of the spinal cord, and melanotic schwannoma. When examined through the lens of embryology, pigmented lesions share a unifying connection: They occur in structures that are neural crest cell derivatives. Here, we review the important progress made in the embryology of neural crest cells, present 3 cases of pigmented tumors of the nervous system, and discuss these clinical entities in the context of the development of melanoblasts. Pigmented lesions of the nervous system arise along neural crest cell migration routes and from neural crest-derived precursors. Awareness of the evolutionary clues of vertebrate pigmentation by the neurosurgical and neuro-oncological community at large is valuable for identifying pathogenic or therapeutic targets and for designing future research on nervous system pigmented lesions. When encountering such a lesion, clinicians should be aware of the embryological basis to direct additional evaluation, including genetic testing, and to work with the scientific community in better understanding these lesions and their relationship to neural crest developmental biology.