A case report of anthracosilicotic spindle-cell pseudotumor of mediastinal lymph node: cytologic diagnosis by endoscopic ultrasound-guided fine-needle aspiration.

Pigmented spindle-cell tumors of the lymph nodes have a broad differential diagnosis, including both benign and malignant neoplasms. Here, we report a case of a pigmented spindle-cell lesion in a mediastinal lymph node mimicking a spindle-cell melanoma on fine-needle aspiration cytology. Smears showed atypical polygonal and spindle cells with bland nuclear features and abundant cytoplasmic anthracotic pigment. Immunohistochemistry was negative for melanoma markers, but showed positivity for histiocyte markers. Polarization microscopy revealed minute birefringent intracellular crystals consistent with silica. Electron microscopy was confirmatory and a diagnosis of anthracosilicotic spindle-cell pseudotumor was made. To the best of our knowledge, fine-needle aspiration cytology findings of this lesion have not been reported.