Fine needle aspiration cytology of a mediastinal granular cell tumor with histologic confirmation and ancillary studies. A case report.

BACKGROUND: Mediastinal granular cell tumors (GCT) are extraordinarily rare and have not been previously reported in the cytology literature. Fine needle aspiration (FNA) cytology of GCT resembles the cytologic features of several other lesions that are more common in the mediastinum. CASE: A middle-aged female with a recent onset of non-productive cough and otherwise unremarkable medical history presented with a mediastinal mass. Imaging studies confirmed the presence of a large mass in the superior, posterior mediastinum closely apposed to the apex of the left lung. FNA revealed scattered large, polygonal to spindle cells with granular cytoplasm and indistinct cell borders. The cytologic differential diagnosis included a benign neural tumor with granular cell features versus GCT. Histologic examination of the surgically resected mass along with supportive immunohistochemical and electron microscopic studies confirmed GCT. CONCLUSION: This is the first reported case of FNA cytology of a mediastinal GCT. A reliable diagnosis can be made with aspirated material from these lesions based upon the characteristic cytologic, immunocytochemical and ultrastructural features of the tumors.