Image-Guided Biopsy: USG and CT Techniques

What is it?

Pre-Procedure Steps (Common to Both USG and CT)

1. Case Selection & Contraindications

• Most biopsies are done under local anaesthesia ± sedation; GA may be used in children
• Contraindications: Uncorrected coagulopathy, no safe needle approach route
• Check for anticoagulant use — timing around anticoagulant cessation must be planned
• Obstructed organs (e.g. bile duct, kidney) should be decompressed first (biliary drainage / nephrostomy) before biopsy
• Vascular lesions carry higher bleeding risk — cross-matched blood may be arranged

2. Preprocedural Assessment

• Review imaging, plan approach, choose guidance modality
• Patient consent (written) + information leaflets
• Optimise patient position to identify safest needle route before starting
• Establish IV access; cross-match blood if high-risk

Needle Types: FNA vs Core Biopsy

Core Needle Devices

• Semiautomatic (e.g. Temno): the central notched stylet is advanced to the target, then the cutting sheath is fired over it — no extra forward excursion, safer near vessels
• Fully automatic (e.g. Achieve, BioPince, Bard Max-Core): both stylet and cutting sheath fire together with a preset "throw" (1–2 cm ahead of the tip) — more force for fibrous lesions, but the operator must ensure the throw doesn't exceed the lesion

Coaxial Technique

Ultrasound-Guided Biopsy

Technique — Step by Step

1. Position the patient — optimise to bring the target as close to the transducer as possible
2. Sterile prep — skin cleaned with povidone-iodine, sterile transducer cover and gel applied, sterile drapes placed
3. Plan the approach — identify the lesion and safest needle path on USG, avoiding vessels, bowel, pleura
4. Local anaesthesia — 1% lidocaine injected superficially (skin wheal, 25G) and then deeper along the planned needle track, under real-time USG guidance
5. Skin nick — a small incision is made with a scalpel at the needle entry site (for core biopsy)
6. Needle insertion — the needle is introduced in the same plane as the ultrasound beam ("in-plane" technique) so the entire needle shaft is visible as an echogenic line; needle guides (attached to the transducer) can assist alignment
7. Real-time targeting — the needle tip is advanced to the lesion under continuous live imaging; tip visibility is improved by:
   • Bevel facing upward
   • Gently "jiggling" the needle
   • Injecting a tiny volume of air or local anaesthetic
   • Roughened/polymer-coated needle tips that scatter ultrasound
8. Firing the device — core biopsy gun is fired; the sample is retrieved from the notch
9. Multiple passes — typically 2–4 cores are taken; with coaxial technique, the outer needle stays in place between passes
10. Haemostasis — firm pressure applied for 10+ minutes; bleeding assessed with colour Doppler
11. Immediate post-procedure scan — to check for haematoma

USG-guided core biopsy: the sterile-sheathed probe visualises the lesion in real time while a spring-loaded biopsy gun delivers the needle at an oblique angle into the target.

Sonographic appearance during biopsy: the 14G core needle appears as a bright echogenic linear structure traversing the hypoechoic target mass.

CT-Guided Biopsy

Technique — Step by Step

1. Scout CT scan — patient placed in CT gantry; a preliminary scan identifies the lesion and plans the needle path (angle, depth, level of entry)
2. Grid / gantry angulation — a radiopaque grid or laser lines on the gantry mark the skin entry point; if needed, gantry tilt is used for oblique approaches
3. Patient positioning — optimised (prone, supine, lateral) to get the safest angle to the target while avoiding critical structures (vessels, nerves, pleura)
4. Sterile prep and local anaesthesia — same as USG; lidocaine infiltrated down to the target level
5. Skin nick and needle insertion — the needle is advanced in the intended direction toward the target; breath-hold instruction reduces respiratory motion artefact for thoracic/abdominal lesions
6. Confirmation CT — a limited scan (or CT fluoroscopy in real-time systems) is acquired to check needle position; adjustments are made and confirmed with repeat CT
7. Coaxial approach — the outer coaxial needle is confirmed at the lesion margin; the inner biopsy needle is then fired through it — particularly important for lung to minimise pleural passes
8. Sample acquisition — multiple cores taken; for centrally necrotic tumours, the periphery of the lesion is targeted (viable tissue, not necrotic centre)
9. Post-procedure CT — a scan is taken immediately after to check for pneumothorax (lung biopsies), haemorrhage, or other complications

Modality Comparison at a Glance

Post-Procedure Care (Both Modalities)

• Observation for 4 hours (vital signs, pain, bleeding)
• Post-lung biopsy: CXR or CT to exclude pneumothorax
• Simple analgesia (NSAIDs) for pain
• Avoid strenuous activity for 24–48 hours
• No driving on the day of procedure
• Results typically available within a few days (histology lab)

Image-Guided Biopsy vs Surgical Biopsy

The Core Concept

Types of Surgical Biopsy

Head-to-Head Comparison

When Each is Chosen

Image-Guided (USG/CT) is preferred when:

• Lesion is accessible and can be visualised on imaging
• A tissue diagnosis is needed before planning definitive therapy (e.g. confirming metastasis to avoid unnecessary surgery)
• Patient is a poor surgical candidate (coagulopathy, comorbidities)
• For staging cancer — confirming nodal or distant disease
• Deep lesions (retroperitoneum, lung, liver, bone) not easily reached surgically without major dissection

Surgical Biopsy is used when:

• Core needle biopsy yields nondiagnostic or inconclusive results after adequate attempts
• The lesion is suspected lymphoma — architecture of the entire node is essential for subtype classification, flow cytometry, and molecular studies
• Very small superficial lesions where excisional biopsy = diagnosis + treatment in one step
• Technically impossible needle biopsy (no safe needle path)
• Surgeon needs to excise with clear margins from the outset (e.g. melanoma, small breast lesion)

Critical Surgical Biopsy Rules (when open is done)

1. Incision orientation — for extremity tumours, incisions must be along the long axis (longitudinal), never transverse — a transverse incision contaminates a wider field and can compromise subsequent limb-sparing resection
2. No undermining — avoid dissecting into surrounding subcutaneous layers; it spreads disease
3. Meticulous haemostasis — a haematoma seeds tumour cells into tissue planes and makes follow-up physical examination very difficult
4. Directly overlie the target — the incision must be directly over the lesion, not tunnelled from a distant site (tunnelling contaminates a larger field)
5. No enucleation — never shell a sarcoma out of its pseudocapsule without a margin
6. Orient the specimen — sutures/clips mark margins; pathologist inks them to determine if margins are clear
7. Plan for re-excision — biopsy scar must be oriented so it can be excised if repeat surgery is needed

The Sampling Error Problem

Core needle biopsy samples only a tiny sliver of tissue. If that sliver is not representative (e.g. it samples the necrotic centre, a reactive area, or misses a small focus of malignancy), the result is false negative. This is especially relevant in:

• Atypical ductal hyperplasia of the breast (19–44% upgraded to carcinoma on excision)
• Heterogeneous tumours
• Very small lesions

Summary in One Sentence Each

• Image-guided biopsy = minimally invasive, low risk, fast, good for most solid tumours — but small sample, possible sampling error, inadequate for lymphoma
• Surgical biopsy = invasive, morbid, expensive — but maximum tissue, definitive architecture, needed when needle fails or lymphoma is suspected, and excisional biopsy can be simultaneously curative