DOI: 10.1148/rg.246035225
RadioGraphics 2004;24:1714-1718
© RSNA, 2004
Metastatic Melanoma: An Unusual Diagnosis for a Large Anterior Mediastinal Mass1
Barbara Loewenthal, MD,
Maria C. Shiau, MD and
Roger Garcia, MD
1 From the Departments of Radiology (B.L., M.C.S.) and Pathology (R.G.), Beth Israel Medical Center, 1st Ave at 16th St, New York, NY 10003. Received December 15, 2003; revision requested January 20, 2004, and received March 1; accepted March 8. All authors have no financial relationships to disclose. Address correspondence to B.L. (e-mail: barbloew@hotmail.com).
Index Terms: Mediastinum, neoplasms, 673.337 • Melanoma, 673.337 • Thorax, neoplasms, 673.337
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History
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A 52-year-old woman presented with a nonproductive cough, mild dyspnea, and chest pain. The patient’s medical history was significant for melanoma diagnosed in 1986. The melanoma was localized to the upper left side of her back and was treated with surgical resection. Otherwise, the patient’s surgical history and medical history were unremarkable. Her family medical history was significant for lymphoma (mother) and colon cancer (sister). The patient smoked 1.5 packs of cigarettes a day for 20 years.
The patient was afebrile and in no significant apparent distress at the time of presentation. She had no reported cervical or axillary lymphadenopathy at physical examination. Her oxygen saturation was 95% on room air. The laboratory values were normal except for iron deficiency anemia and a mildly elevated erythrocyte sedimentation rate of 36 mm/h (normal <30 mm/h).
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Imaging Findings
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Conventional chest radiography demonstrated a large anterior mediastinal mass projecting over the right hemithorax and right hilum. The mass measured approximately 12.5 x 7.6 x 6.6 cm. A right subpulmonic pleural effusion was also identified (Fig 1).
Computed tomography (CT) of the chest, abdomen, and pelvis was then performed. Multiple spiral axial sections through the liver were obtained without intravenous administration of contrast material and during the hepatic arterial phase. Multiple spiral axial sections through the chest, abdomen, and pelvis were obtained during the portal venous phase. Oral contrast material was used.
CT revealed a large mass in the anterior mediastinum to the right of midline, measuring 10.2 x 4.6 cm in cross section (Fig 2a). The mass was heterogeneous in attenuation and contained areas of probable necrosis. The differential diagnosis for this mass included lymphoma, thymic carcinoma, and metastatic disease. CT also demonstrated a 0.8-cm mass in the left upper lobe and a 1.7 x 1.0-cm nodule at the right lung base abutting the right hemidiaphragm (Fig 2b). These small nodules were suspicious for metastasis, although primary bronchogenic carcinoma could not be excluded. There was a small right pleural effusion and no left pleural effusion. Multiple small (<1 cm) lymph nodes were seen in the anterior mediastinum.
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Figure 2a. (a) Contrast-enhanced CT scan shows the large, heterogeneous, low-attenuation mass in the anterior mediastinum and a low-attenuation mass in the left atrium. The small right pleural effusion is also seen. (b) CT scan (lung window) shows a small nodule at the right lung base that abuts the pleural surface.
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Figure 2b. (a) Contrast-enhanced CT scan shows the large, heterogeneous, low-attenuation mass in the anterior mediastinum and a low-attenuation mass in the left atrium. The small right pleural effusion is also seen. (b) CT scan (lung window) shows a small nodule at the right lung base that abuts the pleural surface.
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A heterogeneous, low-attenuation mass was seen in the left atrium abutting the interatrial septum, measuring 5.1 x 3.4 cm (Fig 2a). This mass was suspicious for a myxoma, although sarcoma or metastasis could not be excluded.
The abdominal and pelvic organs appeared unremarkable with no retroperitoneal or pelvic lymphadenopathy. There was no ascites.
Magnetic resonance (MR) imaging of the chest was performed by using electrocardiographically gated gradient-echo acquisitions. Fat-saturated double inversion-recovery and cine gradient-echo imaging was also performed. The large right mediastinal mass, the 1-cm nodular mass in the left upper lobe, and the 5.4 x 2.8 x 4.7-cm left atrial mass were again evident. The mediastinal mass appeared to be focally invading the anterior chest wall (Fig 3). These three masses all had similar signal intensity characteristics with different pulse sequences, a finding thought to be consistent with metastatic melanoma.
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Figure 3. Axial fat-saturated double inversion-recovery MR image shows the large mass of the right upper lobe and anterior mediastinum abutting the anterior chest wall. The left atrial mass is also seen and demonstrates similar signal intensity characteristics.
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Pathologic Evaluation
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After completion of imaging, a CT-guided biopsy of the large anterior mediastinal mass was performed. Histologic analysis of the biopsy specimen revealed malignant melanoma with necrosis, fibrous scarring, and melanin-containing cells (Fig 4).
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Figure 4. Malignant melanoma metastatic to the lung. High-power photomicrograph (original magnification, x20) of the mediastinal mass shows large pleomorphic cells with prominent nucleoli. Some of the cells contain melanin.
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The patient then underwent total surgical resection of the anterior mediastinal mass, total resection of the left atrial mass, and a wedge resection of the right lower lobe mass.
Gross pathologic examination of the anterior mediastinal mass showed an irregular, brownish gray lobulated tissue mass measuring 12 x 11 x 6 cm and weighing 229 g. Serial sections revealed multiple lobulated tan-brown areas of soft to firm tissue with areas of hemorrhage (Fig 5). The wedge resection of the right lower lobe consisted of a wedge of lung tissue stapled at one end, measuring 3 x 1.5 x 1 cm. An irregular brownish black mass was seen on the pleural surface measuring 2 x 1.7 x 0.3 cm. The left atrial mass was irregular, red-tan, and soft (gelatinous) with tan rubbery areas and measured 4.5 x 4 x 3.5 cm.
Results of histologic analysis of the left atrial mass were consistent with a cardiac myxoma (Fig 6) containing a prominent acid mucopolysaccharide background with interspersed round, plump cells. The mediastinal mass was malignant melanoma, as mentioned earlier. Fragments of adipose tissue and striated muscle were seen in contact with the mediastinal mass. The right lower lobe mass was also malignant melanoma. The melanoma reached the margin of the resection and invaded through the visceral pleura (Fig 7). The diagnoses were confirmed by an AFIP pathologist.
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Figure 6. Cardiac myxoma. High-power photomicrograph (original magnification, x40) shows a prominent acid mucopolysaccharide background with interspersed round, plump, and stellate cells, some in a cordlike arrangement.
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Figure 7. Malignant melanoma metastatic to the lung. Photomicrograph (original magnification, x2) shows the poorly circumscribed hyperchromatic mass extending to the visceral pleura.
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Discussion
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Metastatic melanoma manifesting as a large mediastinal mass is rare with only a few reports in the literature. Lau et al (1) discussed a case of a patient with a right paratracheal mass and extensive mediastinal lymphadenopathy. That patient’s histologic studies revealed malignant melanoma consistent with metastases in lymph nodes. Unlike that reported case, the patient presented herein had no apparent lymph node involvement at either radiologic or pathologic evaluation, which is unusual in metastatic melanoma to the mediastinum.
Metastasis to the mediastinum may originate from primary malignancies of the esophagus or lung or from extrathoracic tumors. In these cases, the sites of involvement are invariably lymph nodes (2); however, metastatic involvement of mediastinal and hilar lymph nodes is less common than pulmonary parenchymal involvement (3). In a review of 1,071 cases of extrathoracic malignancy, McLoud et al (4) noted that standard radiographs demonstrated mediastinal or hilar nodal involvement in 2.3% of cases. Head and neck tumors accounted for a majority (eight of 25) of the cases, followed by testicular tumors, renal cell carcinomas, breast carcinomas, and melanomas (two of 25). When nodal involvement was present, pulmonary involvement with lymphangitic spread or parenchymal nodules was noted concomitantly in 40%.
The lungs serve as a filter for tumor emboli in malignancies in which venous drainage flows directly into the lungs. Such tumors have a high frequency of pulmonary metastases without other distant metastases. These tumors include tumors of the head and neck, osteosarcoma, testicular carcinoma, and melanoma (5). Melanomas account for a sizable percentage of lesions that metastasize to the thorax. Five percent of cases of metastases to the mediastinum and lung are due to melanoma (2).
Chen and colleagues (6) studied a series of 1,600 patients treated for malignant melanoma at one institution and found that 260 (16.3%) developed thoracic metastases. In that series, the chest radiographs showed mediastinal or hilar lymphadenopathy in 7% of the intrathoracic metastases, multiple pulmonary nodules in 40%, solitary nodules in 10%, and pleural effusions in 2%. Fifty percent of patients with pulmonary nodules due to metastatic melanoma will also have enlarged mediastinal and hilar lymph nodes (2). In these patients, there is likely spread of tumor to the mediastinal and hilar lymph nodes along pulmonary lymphatics (7).
To review, the patient presented herein had a parenchymal nodule (right lower lobe) that was consistent with metastatic melanoma and a large mediastinal mass that was also malignant melanoma. On the basis of a review of the literature by Chiles and Ravin (7) and Viadana et al (5), the likely pathogenesis of the parenchymal nodule is that it probably spread from venous drainage from the primary cutaneous melanoma. The pathogenesis of the large mediastinal mass is that it probably resulted from lymphatic spread from the parenchymal nodule in the right lower lobe to the mediastinal lymph nodes. The mass probably outgrew the lymph nodes, resulting in a large anterior mediastinal tumor (with no apparent lymph node involvement at radiologic or pathologic evaluation).
Primary malignant melanoma of the mediastinum is extremely rare with only a few reports in the literature (8), making this very unlikely in this patient who had a known primary melanoma. The melanotic tumors of the mediastinum are rare and include pigmented extraadrenal paraganglioma, pigmented carcinoid tumor of the thymus, melanotic schwannoma, melanotic neuroectodermal neoplasm, and primary malignant melanoma (8).
Nearly 30% of patients with melanoma develop metastatic disease (stage 4) (9). The long-term survival for these patients is poor, with only 4% of patients alive at 4 years (10). Surgical resection is a consideration in patients with isolated metastases in the brain, bowel, or lungs. Surgical treatment of lung metastases from melanoma is controversial, as the expected outcome is poor. Leo et al (11) performed a retrospective analysis of 328 patients who underwent lung metastectomy for melanoma between 1945 and 1995. After complete pulmonary metastectomy, the 5- and 10-year survival was 22% and 16%, respectively. There were no long-term survivors after incomplete resection. In that group of patients, a time to pulmonary metastases of shorter than 36 months and the presence of multiple metastases were unfavorable prognostic factors for surgery. Patients without these risk factors (single lesion and time to pulmonary metastases of >36 months) experienced the best survival (29% at 5 years).
Novel treatment approaches are now being used to treat advanced metastatic melanoma in non–surgical candidates or in addition to surgical palliation. Single-agent chemotherapy with dacarbazine has been ineffective, with a response rate of only 10%–20% in the treatment of metastatic melanoma (10). There was a slightly improved response rate for combination chemotherapy, but this was not statistically significant and the toxicity was greater. Tamoxifen has been studied for use in the treatment of advanced melanoma, as portions of melanoma cells were recognized to express estrogen receptors. However, the more recent, larger randomized trials have failed to find a supportive role for its use (10).
Recently, new innovative treatment strategies for the treatment of metastatic melanoma have focused on immunotherapy. The presence of natural immune responses is illustrated by spontaneous regression of melanoma at the site of the primary lesion, with infiltrating macrophages and lymphocytes seen at this site (12). Interferons are a group of endogenously produced cytokines with immunomodulatory effects. Interferon-alpha-2b has been extensively studied and has demonstrated benefit in the treatment of resected melanoma at risk for recurrence (13). Interferon-alpha-2b and interleukin-2 have been approved by the U.S. Food and Drug Administration for the treatment of metastatic melanoma (12). Current studies are also exploring the use of vaccines for the possible treatment of advanced melanoma.
In conclusion, this was an unusual case of metastatic melanoma manifesting as a large mediastinal mass. (Incidentally, as discussed, this patient also had an atrial myxoma.) Melanoma frequently metastasizes to the thorax, including to the mediastinal and hilar lymph nodes, but there is little information in the literature on metastatic melanoma manifesting as a large anterior mediastinal mass. This patient is currently being treated with adjunctive chemotherapy.
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References
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- Lau C, Bentley R, Gockerman J, Que L, D’Amico T. Malignant melanoma presenting as a mediastinal mass. Ann Thorac Surg 1999; 67:851-852.[Abstract/Free Full Text]
- Webb WR, Gamsu G. Thoracic metastasis in malignant melanoma: a radiographic survey of 65 patients. Chest 1977; 71:176-181.[Abstract]
- Snyder B, Pugatch R. Imaging characteristics of metastatic disease to the chest. Chest Surg Clin N Am 1998; 8:29-48.[Medline]
- McLoud TC, Kalisher L, Stark P, Greene R. Intrathoracic lymph node metastases from extrathoracic neoplasms. AJR Am J Roentgenol 1978; 131:403-407.[Abstract]
- Viadana E, Bross I, Pickren J. Cascade spread of blood-borne metastases in solid and nonsolid cancers in humans. In: Weiss L, Gilbert H, eds. Pulmonary metastases. Boston, Mass: Hall, 1978; 143-167.
- Chen J, Dahmash N, Ravin C, et al. Metastatic melanoma to the thorax: report of 130 patients. AJR Am J Roentgenol 1981; 137:293-298.[Abstract/Free Full Text]
- Chiles C, Ravin C. Intrathoracic metastases from an extrathoracic malignancy: a radiographic approach to patient evaluation. Radiol Clin North Am 1985; 23:427-438.[Medline]
- Vlodavsky E, Ben-Izhak O, Best L, Kerner H. Primary malignant melanoma of the anterior mediastinum in a child. Am J Surg Pathol 2000; 24:747-749.[CrossRef][Medline]
- Legha S. Treatment of metastatic melanoma. Cancer Control 1999; 6:398-404.[Medline]
- O’Day S, Kim C, Reintgen D. Metastatic melanoma: chemotherapy to biochemotherapy. Cancer Control 2002; 9:31-38.[Medline]
- Leo F, Rocmans P, Cappello M. Lung metastasis from melanoma: when is surgical treatment warranted? Br J Cancer 2000; 83:569-572.[CrossRef][Medline]
- Faries M, Morton D. Melanoma: is immunotherapy of benefit? Adv Surg 2003; 37:139-169.[Medline]
- Terando A, Sabel MS, Sondak VK. Melanoma: adjuvant therapy and other treatment options. Curr Treat Options Oncol 2003; 4:187-199.[Medline]
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History
Imaging Findings
