Fine needle aspiration (FNA) cytology is a diagnostic technique that uses a thin-gauge needle to aspirate cells from palpable or image-detected lesions. It provides a definitive diagnosis in minutes when rapid on-site evaluation (ROSE) is available, and offers a safer, faster, and less expensive alternative to core needle biopsy for many indications.
Technique
Palpation-guided FNA — the lesion is immobilized with one hand while the other hand advances the needle. The needle is moved back and forth within the lesion (10-20 rapid passes) while maintaining negative pressure with a syringe (10-20 mL). Pressure is released before withdrawing the needle to prevent aspiration into the syringe. The needle contents are expelled onto slides by reattaching the syringe filled with air. For vascular lesions, FNA without suction (capillary or “non-aspiration” technique) reduces blood dilution.
Image-guided FNA — ultrasound, CT, or endoscopic ultrasound (EUS) guidance targets deep-seated lesions (pancreas, liver, lung, mediastinum, retroperitoneum). Real-time visualization ensures needle placement within the lesion, avoids necrotic areas, and avoids adjacent vessels.
Rapid On-Site Evaluation (ROSE)
ROSE is performed by a cytotechnologist or pathologist in the procedure room. One slide is stained immediately (Diff-Quik or Toluidine Blue) and examined under a microscope. ROSE confirms that the specimen is adequate (contains diagnostic cells from the target lesion), triages the specimen for ancillary studies (cell block for IHC, culture, flow cytometry), and provides a preliminary diagnosis that guides immediate clinical decisions. ROSE reduces inadequate rates from 15-25% to <5%, avoids repeat procedures, and saves healthcare costs.
Organ-Specific Applications
Thyroid FNA is the standard test for evaluating thyroid nodules. The Bethesda System for Thyroid Cytology categorizes results into six diagnostic categories with implied malignancy risk: nondiagnostic (5-10%), benign (0-3%), atypia of undetermined significance (10-30%), follicular neoplasm (25-40%), suspicious for malignancy (50-75%), and malignant (97-99%). Molecular testing (ThyroSeq, Afirma) refines risk in indeterminate categories.
Breast FNA evaluates palpable and image-detected breast lesions. Triple test combines clinical examination, imaging (mammography, ultrasound), and FNA for a near-100% diagnostic accuracy when all three are concordant. FNA is also used for axillary lymph node staging in breast cancer patients.
Lymph node FNA diagnoses reactive hyperplasia, granulomatous inflammation (tuberculosis, sarcoidosis), infections, and metastatic malignancy. Flow cytometry of FNA material diagnoses and classifies non-Hodgkin lymphomas. FNA is the first-line diagnostic modality for suspected lymphoma in accessible nodes.
Salivary gland FNA distinguishes neoplastic from non-neoplastic lesions and benign (pleomorphic adenoma, Warthin tumor) from malignant (mucoepidermoid carcinoma, adenoid cystic carcinoma) neoplasms. Specificity exceeds 95% for malignancy.
Pancreatic FNA (EUS-guided) diagnoses pancreatic ductal adenocarcinoma, neuroendocrine tumors, and cystic lesions (with cyst fluid analysis for CEA and amylase). Sensitivity for pancreatic adenocarcinoma is 80-95% with ROSE.
Lung FNA — endobronchial ultrasound (EBUS)-guided FNA of mediastinal and hilar lymph nodes diagnoses and stages lung cancer. Transbronchial FNA targets peripheral lung nodules. IHC on cell blocks determines tumor subtype (adenocarcinoma vs. squamous vs. small cell) and molecular markers (TTF1, p40, PD-L1).
Diagnostic Challenges
False-negative FNA results from sampling error (needle misses the lesion), necrotic tumors, desmoplastic tumors that yield few cells, and small lesions (<1 cm). Re-aspiration or core needle biopsy resolves most false negatives. False-positive FNA is rare but can occur from interpreting reactive atypia or repair changes as malignant, or from contaminating normal cells. Correlation with clinical and imaging findings is essential.
Complications
Complications are rare (<1%). Bleeding and hematoma are the most common, managed by prolonged pressure. Pneumothorax complicates 1-5% of lung FNAs; most are managed conservatively. Infection, needle tract seeding (extremely rare, <0.01%), and vasovagal reactions are reported. FNA of carotid body tumors and pheochromocytoma carries a risk of hypertensive crisis.
