Primary malignant melanoma in the mediastinum is extremely rare, with only a few cases reported to date (1
). These tumors have been diagnosed only in patients with no history of extrathoracic primary melanoma or other malignancy.
Histologically, melanomas are malignant tumors composed of melanocytes, which are derived from neural crest cells. Neural crest cells are transient and multipotent cells that develop into melanocytes, peripheral and enteric neurons and glia, craniofacial cartilage and bone, and smooth muscle (6
). Malignant melanoma most often develops in the skin, but also occurs in the eyes, oronasal mucosa, and anorectal junction, all sites of melanin cell occurrence.
Nevus cells are a variant of melanocytes found in lymph nodes and the thymus. Aggregates of nevus cells in the thymus or a mediastinal lymph node may be sources of malignant melanomas in the anterior mediastinum (5
). The autonomic ganglion cells are similarly derived. A case of malignant melanoma of the posterior mediastinum arising from the sympathetic chain was reported (7
We describe here two patients with huge primary malignant melanomas of the anterior mediastinum. Computed tomography showed that primary malignant melanomas were found to be lobulated masses with mild enhancement in the anterior mediastinum. In both of our patients, the mediastinal masses appeared to involve the pericardium, pleura and lymph nodes, along with distant metastases. MRI scans were not performed in our cases.
A previous case report described the findings on magnetic resonance imaging of a primary malignant melanoma in the anterior mediastinum (4
). The mass was mildly hyperintense to muscle on T1-weighted images and heterogeneously hypointense to muscle on T2-weighted images. When correlated with pathology findings, the focal areas of T1 hyperintensity and T2 hypointensity were found to be composed of melanocytes with rich melanin granules (4
The major considerations of differential diagnosis of primary malignant melanoma in anterior mediastinum include a lymphoma, thymic carcinoma, malignant germ-cell tumor, and, more rarely, a mediastinal soft tissue sarcoma such as an angiosarcoma.
The prognosis of primary malignant melanoma in mediasinum is unfavorable and surgical resection is the best treatment. Systemic chemotherapy and immunotherapy can be used to treat advanced disease (8
In conclusion, although rare, primary malignant melanoma in the anterior mediastinum can present as a large mediastinal mass with displacement or invasion of the adjacent mediastinal structure, metastatic mediastinal lymph nodes and distant metastasis, similar to CT imaging patterns of other malignant mediastinal masses.