Primary CNS melanocytic tumor of intermediate type progressing to metastatic melanoma.
Primary melanocytic tumors of the central nervous system are rare. Their estimated incidence is 0.9 per 10 million (1). Melanocytes originate from neural crest cells during early embryonic development. Histologically these tumors belong to a spectrum, which ranges from a well-differentiated melanocytoma at one end to a highly malignant aggressive tumor at the other extreme. The term "Intermediate grade" has been proposed for melanocytic tumors which could not be classified as melanocytomas or melanomas. In the case presented here an initial diagnosis of an intermediate grade melanocytic tumor was made following which the patient re-presented 9 months later with renewed neurological deficit and underwent a further surgery. Histopathology revealed that the tumor had progressed to a highly malignant form consistent with a malignant melanoma. Post mortem examination revealed that there was widespread meningeal metastatic spread of the tumor, which was also apparent on repeat imaging.
Three previous cases have been identified in the literature: of these, one tumor recurred locally after 17 months, one patient was lost to follow-up, and the third patient died after surgery (2). Histologically it is inferred that those tumors of intermediate grade progressed to an aggressive melanoma but due to the lack of a large series of patients this is not conclusive.
This is the first reported case in which the patient progressed with diffuse CNS disease instead of localised recurrence indicating further the potential aggressive nature of an intermediate grade melanocytic tumor. There are no clear-cut guidelines in the management of these patients and the management is the same as that for patients diagnosed with primary melanomas. The prognosis of primary CNS melanomas is poor: only 20% survive more than 12 months (3). Primary melanomas of CNS may present either with localised intra/extra-axial mass lesions or meningeal spread, which carries a worse prognosis. Patient undergoing complete excision during surgery has been shown to have the longest survival time (4). There are no clear-cut guidelines with regards to the usefulness of adjuvant therapy, such as radiotherapy, chemotherapy and immunotherapy. The use of radiotherapy in metastatic melanoma has been associated with some response (5). In conclusion it is noted that there is no preferred treatment options for post-surgery treatment, but there is overall agreement that total excision of the lesion at the initial surgery is the role of surgical management.
Contributed by R. Abeygunaratne, G. Roberts, L. Gunawardena, J. Joseph and T. Dawson