Spindle cell and mesenchymal lesions of the lung encompass a wide variety of benign and malignant conditions. However, to the authors' knowledge, because of their rarity, few reports concerning their cytologic findings are available in the literature. The current review emphasizes the cytomorphologic features, differential diagnosis, and potential pitfalls associated with these lesions.
Seven hundred seventy-nine percutaneous lung fine-needle aspiration (FNA) specimens were retrieved from the authors' cytopathology files over a period of 5 years. Sixty-one cases (7.8%) in which a spindle cell component was the dominant or key feature were identified. The authors reviewed the cytologic smears, immunocytochemical studies, and corresponding surgical material and clinical information.
Of these 61 aspirates, 33 (54%) were reactive processes (31 granulomas, 1 organizing pneumonia, and 1 inflammatory pseudotumor). Five cases (0.8%) were benign neoplasms (2 hamartomas, 2 solitary fibrous tumors, and 1 schwannoma). Twenty-three cases (38%) were malignant neoplasms (8 cases were primary tumors [including 5 carcinomas with spindle cell or sarcomatoid features, 1 spindle cell carcinoid tumor, 1 leiomyosarcoma, and 1 synovial sarcoma] and 15 cases were secondary tumors [including 9 melanomas, 2 leiomyosarcomas, 1 malignant fibrous histiocytoma, 1 meningioma, 1 sarcomatoid renal cell carcinoma, and 1 uterine malignant mixed müllerian tumor]). A specific diagnosis was rendered in 52 cases (85%). No false-positive cases were encountered but there was one false-negative case. One patient who was diagnosed with granulomatous inflammation on FNA was found to have nonsmall cell lung carcinoma on subsequent transbronchial biopsy. No malignant cells were identified in the smears on review. The FNA from the organizing pneumonia was interpreted as a solitary fibrous tumor whereas the inflammatory pseudotumor was diagnosed as granulomatous inflammation. The FNA from one pulmonary hamartoma initially was considered to be nondiagnostic. One solitary fibrous tumor and the schwannoma were diagnosed as smooth muscle tumor and spindle cell tumor, not otherwise specified, respectively. Among the malignant tumors, the primary synovial sarcoma and one of the metastatic malignant melanomas initially were interpreted as primitive neuroectodermal tumor/Ewing sarcoma and poorly differentiated carcinoma, respectively.
Spindle cell lesions of the lung rarely are encountered on transthoracic lung FNA and are comprised of a wide variety of benign and malignant entities. By correlating clinical and radiologic data, cytologic findings, and ancillary studies, a high diagnostic accuracy rate can be achieved with FNA.