Pathologic findings:
Consists of two fragments of haemorrhagic tissues measuring 1.0 and
1.5 cm in dimension each. Submitted entirely in two blocks. Sections show
fragments of cellular tumour tissues focally accompanied by some adjacent
brain parenchyma. The tumour has very little stroma and show a diffuse
or nesting pattern of growth consistent with melanoma. The tumour cells
have large pleomorphic nuclei with prominent nucleoli. Many are heavily
laden with brownish pigment and features are characteristic of metastatic
malignant melanoma.
| Figure 1 : Low power tumour | Figure 2 : Low power with brain |
| Figure 3 : Medium power tumour | Figure 4 : High power tumour |
Pathologic Diagnosis:
Left parietal tumour - Malignant melanoma, probably metastatic
Pathologist Comments:
Melanocytic tumours of the CNS includes melanocytic schwannoma, melanocytomas, primary and metastatic melanomas. Melanocytomas usually present in middle age or later as circumscribed masses attached to the leptomeninges or dura. Most arise in association with spinal nerve roots. They are composed of variably admixed spindle and epithelioid cells, accompanied by abundant melanin production. Although nucleoli may be prominent, melanocytomas are distinguished from (malignant) melanomas by absence of nuclear pleomorphism, mitosis and necrosis. Differentiation from pigmented (melanotic) schwannoma is often difficult on microscopical features alone but ultrastructural studies are useful. Aggressive neuroparenchymal invasion and CSF seedling are not usual features of melanocytomas. They have a relatively indolent clinical behaviour.
Like metastatic melanoma, primary melanoma can produce pigmented masses in the CNS and they are believed to have arisen from melanocytes that are normally found in the leptomeninges. In addition, they can also present initially as diffuse leptomeningeal tumours and have a high risk for CSF spread. The diffuse pattern of growth is particularly characteristic of childhood examples occurring as part of the neurocutaneous melanosis complex.
Primary melanoma of the CNS can only be diagnosed after meticulous search for a cutaneous, mucosal or ocular primay fail to find any tumour. It is likely that the tumour in this patient could be a metastatic tumour unless a thorough search do not find an obvious primary outside the CNS. The location of this tumour in the parietal region favours a metastatic lesion since the parietal and frontal regions are the most common sites for CNS metastases. Primary melanoma arises from the leptomeninges and thus a deep seated tumour not involving the meninges would favour a metastasis. Multicentricity also favours a metastatic nature.
Distant metastases in melanoma occur most often in the liver, lungs, GIT, bone and CNS but can occur anywhere. Common metastatic tumours to the CNS in descending order of frequencies are lung, breast, melanoma, renocortical carcinomas, adenocarcinoma of colorectal origin.
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