Malignant melanoma of mediastinum misdiagnosed as a spindle cell thymoma in a fine needle aspirate: a case report.

Background: Malignant melanomas in the medastinum are extremely rare. Both primary melanomas and metastatic lesions from a primary elsewhere can occur in the mediastinum. Aspiration biopsy of a melanoma at this unusual site may pose problems in diagnosis.
Case: A 35-year-old woman presented with an anterior mediastinal mass. Cytologic smears were hemorrhaghic and revealed a loosely dispersed population of spindle cells with prominent nucleoli. In view of the location, the possibility of spindle cell thymoma was suggested on cytology. Subsequent histology revealed a malignant melanoma.
Conclusion: This case stresses that the cytopathologist should keep in mind the remote differential diagnosis of a malignant melanoma while evaluating spindle cell neoplasms of the mediastinum, especially in tumors with prominent cell dispersal and with cells that have prominent nucleoli even without melanin pigment. Accurate diagnosis helps in evaluating patients and avoids unnecessary surgery when the lesion represents a metastasis to the mediastinum from a primary elsewhere.