A rare case of malignant melanoma presenting as anterior-superior mediastinal mass
Primary malignant melanoma (MM), although predominantly a tumor of skin, can occur at almost any site in the body where nevus cells/melanocytes are found. Mediastinal malignant melanoma (MEM) is rare as both primary and metastatic lesion. MM accounts for 1.5% of all cancers and arises from a preexisting nevus in 40% of cases . We present an extremely rare case of primary malignant melanoma presenting as a superior mediastinal mass. 

A 65 years-old woman presented to emergency room with a symptomatology characterized by sudden hyposthenia ad tremors in the left arm. Computed tomography (CT) of the brain showed a lesion in the right frontal region measuring 3,2 × 2,6 × 3.3 cm and another smaller lesion in the left temporo-occipital region measuring 1 cm ( , ). These lesions were confirmed at MRI performed later ( , ). For detection of any primary focus, she underwent to CT thorax that showed a solid mass measuring 11 × 10 × 8 cm in the anterior-superior mediastinum on the right side with compression and dislocation of brachiocephalic and azygos vein, compression of trachea and main bronchi and multiple lymphadenopathies ( , , , ). Ct-scan of the abdomen and pelvis revealed no primary or metastatic lesion. Endobronchial ultrasonography-Transbronchial needle aspiration (EBUS-TBNA) was done for tissue biopsy (needle 19G). Histopathologic diagnosis of trans-bronchial needle aspiration revealed malignant melanoma confirmed by immunohistochemically stains positive for SOX 10/Melan and A/HMB45 and BRAF testing of the tumor was ordered. A meticulous search for primary was conducted through examination of the entire skin, eye, genitalia and anal canal and not revealed nevus; there was also no history of any prior surgical resection of a mole. After 3 days the patient developed vena cava syndrome with face and neck swelling, upper extremity swelling, dyspnea, cough, and dilated chest vein collaterals. Brachio-cephalic left wall-stent was placed to solve the vein recanalization with fair resolution of symptoms ( , ). Positron emission tomography (PET) scan remonstrated the large mediastinal mass (SUV 17) ( ) and low FDG uptake in the brain metastases ( , ). The mass was not amenable to surgical resection due to its anatomic location and genetic analysis confirmed the tumor was BRAF positive reason why she began therapy with inhibitors of BRAF and radiation therapy. The first radiological follow-up after starting therapy will be in 2 month. 

Rare reports have reported primary or metastatic melanoma as a mediastinal mass. The most common site of primary MM is the skin but virtually any organ system where melanocytes/nevus cells may be encountered can be become involved . In cases previously described, mediastinal involvement of melanoma was typically reported as primary in origin, may, however present metastatically in the absence of a primary lesion (1%-8% of melanoma) . The differential diagnoses for melanotic tumor of the mediastinum include pigmented extra-adrenal paraganglioma, pigmented carcinoid tumor of the thymus, melanotic schwannoma, melanotic neuroectodermal neoplasm and primary MEM . There are 2 hypotheses to explain MEM as primary lesion: these tumors arise from nevus cell aggregate in mediastinal nodes (in sympathetic chain in posterior mediastinum) or, and it is another plausible pathogenesis, in-utero migration of melanocytes with rest of embryonic respiratory tract from primitive foregut . The prognosis of MEM is unknown due to rarity of disease, however case reports suggest an aggressive clinical course . When corresponding stages were compared, the survival of patients with melanoma of unknown primary was found to be similar to that of patients with known primary. Unfavorable prognosis was observed in patient with stage IV diseases and MEM. Patients with metastatic brain melanomas have very high mortality rates, and the median survival rate after diagnosis is 6 months despite the therapy . 

Cases of malignant melanoma, presenting as mediastinal mass, are extremely rare. This case report adds to our knowledge of the unusual way in which melanoma can present. Despite its rarity, mediastinal melanoma should be considered when evaluating new mediastinal masses. Our patient, with no history of resection of nevus and in absence of primary lesion, is in actual therapy with inhibitors of BRAF and radiation therapy. Rare case reports present in literature suggest a poor prognosis. 

All authors read and approved the final version of the manuscript. All the aforementioned authors had access to the data and a role in writing the manuscript. 

Authors confirm that informed consent for publication was obtained from the patient. 

