Ultrasound & CT-Guided Chiba Needle (FNAB) — Standard Operating Procedure & Practical Tips

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Image-guided Fine Needle Aspiration Biopsy (FNAB)​ using a Chiba needle is a cornerstone diagnostic modality. Below are standardized steps for ultrasound- and CT-guided approaches.

Pre-Procedure Preparation

Labs: coagulation profile, platelet count, renal/liver function

NPO 4–6 h (abdominal targets)

Informed consent

Equipment: 21G/22G (occasionally 20G) Chiba needle, 2–5% lidocaine, 10 mL syringe, glass slides, 95% ethanol (fixative), optional coaxial guide needle

Ultrasound-Guided FNAB

• Mapping:​ Color Doppler to identify perilesional vessels; plan shortest safe path avoiding bowel, gallbladder, pleura.
• Anesthesia:​ Local infiltration to serosal/capsular level.
• Advancement:​ In-plane (preferred) or out-of-plane; real-time visualization of shaft & tip. Pause respiration at end-expiration.
• Aspiration:​ Attach 10 mL syringe; apply 2–5 mL negative pressure; gently fan/move tip 2–3× within lesion; maintain suction while withdrawing.
• Smear:​ Expel material onto slide, smear unidirectionally, fix immediately in 95% ethanol.
• Multiple passes:​ 2–3 separate sites within the same lesion improve adequacy-especially in necrotic tumors.

CT-Guided FNAB (Deep / Obscured Lesions)

Localize entry point & depth on pre-scan; mark skin.

Advance to preset depth; repeat CT to confirm tip within non-necrotic portion of target.

Apply suction, withdraw, smear as above.

Lung nodules:​ Choose shortest trans-pulmonary path; avoid fissures & large vessels; post-procedure CXR to rule out pneumothorax.

Tips to Improve Specimen Adequacy

Orient bevel toward tissue to be sampled; keep bevel submerged in lesion.

• Negative pressure:​ Small (2–3 mL) for hypercellular/vascular lesions (thyroid, lymphoma); slightly higher for fibrous/mucinous lesions.
• Rapid in-and-out:​ Minimize dwell time to prevent lumen clogging.
• Capillary action method:​ For fragile lesions, some operators use no suction - rely on capillary draw.
• ROSE (Rapid On-Site Evaluation):​ Cytotech or pathologist examines smears bedside to confirm adequacy before ending procedure.

Complication Prevention

Overall complication rate <1%:

Self-limited oozing (most common)

Pneumothorax (lung biopsy ~3–5%) - usually resolves spontaneously or with simple aspiration

Rare infection or needle tract seeding (<0.01%)

Post-procedure: compress site ×5–10 min, observe 30 min–2 h.

Mastery of Chiba needle FNAB under dual-modality guidance maximizes diagnostic yield while minimizing risk - a core competency for interventional and ultrasound specialists.