Fine Needle Aspiration — Diagnostic biopsy using a thin needle

Fine needle aspiration (FNA), often referred to as fine needle aspiration biopsy or cytology, involves passing a narrow-gauge needle (typically 22 to 27 gauge) through the skin into a lesion. Negative pressure is applied via an attached syringe to extract free cells and fluid fragments, which are smeared across glass slides for cytopathological evaluation.

The procedure is commonly performed freehand for easily palpable lumps, or under continuous real-time imaging guidance—such as ultrasound, computed tomography (CT), or endoscopic ultrasound—for deep-seated lesions. Cytopathologists inspect cellular architecture, nuclear shapes, and staining characteristics, providing rapid preliminary or definitive diagnostic assessments without requiring surgical excision.

FNA offers an accurate, rapid, and low-risk method to diagnose or rule out cancer at an early stage. Because it requires only local anaesthetic, it avoids the risks, recovery times, and costs associated with surgical biopsies. Accurate cytopathology assists doctors in determining whether additional tests, surveillance, or urgent oncology interventions are warranted. If cells appear benign, it spares patients from unnecessary, invasive surgical procedures and alleviates immense psychological anxiety.

While FNA is itself a diagnostic test rather than an analyte, the extracted cellular material is subjected to diverse laboratory assays. The cytopathologist performs microscopic cytomorphological analysis, supplemented by rapid on-site evaluation (ROSE). The cellular aspirate can also be used for immunocytochemistry, flow cytometry (especially for lymphomas), and molecular biomarker testing, including BRAF, KRAS, or EGFR gene mutations.

Fine needle aspiration is widely utilised to evaluate nodules of the thyroid gland, salivary glands, and palpable or deep lymph nodes. It frequently assists in diagnosing or staging breast cancer, lung cancer, pancreatic adenocarcinoma, head and neck carcinomas, and recurrent metastatic deposits found across various soft tissue locations.

Results from an FNA dictate initial treatment pathways. If the aspirate confirms malignancy, the patient is promptly referred for definitive oncological staging, surgical resection, chemotherapy, or radiotherapy. In ambiguous or non-diagnostic cases, clinicians use the results to justify follow-up core needle biopsy or surgical excision. For benign cysts, the aspiration itself can be therapeutic by draining uncomfortable fluid accumulations.