A case of lung FNA with atypical squamous cells

Fine-needle aspiration (FNA) is a commonly employed method for initial diagnosis and work-up of pulmonary nodules. Utilization of rapid on-site evaluation (ROSE) has the added benefit of allowing for triaging of material as appropriate for ancillary studies including microbiology testing. While many pulmonary lesions are easily categorized by cytologic evaluation, more difficult cases exist. In particular, pulmonary lesions demonstrating atypical squamoid cells can cause diagnostic challenge given the morphologic overlap between benign and malignant pulmonary lesions showing atypical squamoid cells. We herein review these common and uncommon squamoid lesions, which may enter within the differential when encountering atypical squamoid cells in pulmonary FNA specimens with emphasis on morphologic pitfalls and approaches to appropriate categorization.