Fine-Needle Aspiration (FNA) or Core Needle Biopsy
The choice of instrument caliber and technique depends on the diagnostic objective.
- Fine-Needle Aspiration (FNA) is performed with thin needles (20–25 G). The goal is to obtain isolated cells for cytology or to create a cell block for immunohistochemistry. The method is ideal if the needle must pass through bowel loops or near critical vessels (e.g., near the inferior vena cava). It is suitable for debilitated patients since the risk of iatrogenic injury is minimal.
- Core needle biopsy (Core biopsy) is performed using large-caliber cutting needles (14–19 G). It allows obtaining a full-fledged tissue core while preserving its architecture. This is strictly necessary for the primary histologic typing of malignant tumors (e.g., lymphomas) or the diagnosis of diffuse liver diseases (cirrhosis) and kidney diseases (glomerulonephritis).
Cutting needle mechanisms and coaxial system
Instruments for histologic tissue sampling differ in their cutting mechanism:
- Semi-automatic devices (e.g., Temno). The physician positions the central stylet with the notch inside the lesion. Then the cutting cannula "fires" over it. Since the system does not advance forward during the cut (absence of forward excursion), the method is safe for small nodules and targets near major vessels.
- Fully automatic devices (Achieve, Bard Max-Core). The instrument simultaneously fires the stylet and cannula forward by a set step (e.g., 1 or 2 cm). This requires precise calculation: the needle tip is positioned at the superficial edge of the lesion to avoid puncturing through the organ upon firing.
Coaxial technique (coaxial technique) involves placing a thick guiding needle through which a thin biopsy needle is repeatedly introduced. This makes it possible to obtain multiple samples through a single puncture of the organ capsule or pleura. In lung biopsy, this reliably reduces the risk of pneumothorax and theoretically prevents tumor cell seeding along the needle tract (track seeding).
Imaging modalities: pros and limitations
The primary "workhorses" of the radiologist remain ultrasound and computed tomography.
- Ultrasound (Ultrasound). First-line method. Provides real-time imaging, allows multiplanar angled approach (multiplanar angled approach), and involves no radiation exposure for the patient. Especially useful for the liver (minimizes the time the needle spends in the parenchyma). The main drawback is heavy operator dependence.
- CT (Computed Tomography). The gold standard for lungs, bones, and deep abdominal structures. Standard CT does not operate in real time, requiring stepwise control of needle position.
- MRI (Magnetic Resonance Imaging). Indispensable when the lesion is visible only on MR scans (e.g., in the peripheral zone of the prostate apex) or when a complex oblique approach (oblique approach) is required. The method is expensive, time-consuming, requires MR-compatible (non-magnetic) needles, and is unsuitable for patients with pacemakers.
Navigation and patient management guidelines
An experienced clinician always plans the trajectory and considers tissue properties.
- Overcoming poor visualization: If the needle tip is lost in deep or echogenic structures on ultrasound, turn the needle bevel (bevel) upward, gently jiggle it in the tissues ("jiggling"), or inject a drop of air/anesthetic for acoustic contrast.
- Avoiding uninformative samples: In massive tumors, areas of central necrosis should be avoided (gelatinous material will not yield a diagnosis). The needle should be directed through the viable periphery of the lesion.
- Anesthesia and monitoring: Post-procedural pain is normal and managed with NSAIDs. However, if a patient requires opiates, this is a "red flag"—hemorrhagic complications must be urgently ruled out.
Briefly: answers to topical questions
What are the absolute and relative contraindications for percutaneous biopsy?
The sources indicate the following contraindications and limitations for percutaneous biopsy.
- Contraindications for image-guided biopsy include uncorrected coagulopathy (uncorrected coagulopathy) and the absence of a safe access path for needle insertion.
- For pleural/chest wall interventions: absolute contraindications are hemorrhagic diatheses (haemorrhagic diatheses); relative contraindications are the patient's inability to control breathing and/or coughing.
Before the procedure, it is essential to carefully weigh the benefits of confirming the diagnosis against the inherent risks of the procedure itself. In patients with coagulopathy or those taking anticoagulants, careful planning of the biopsy timing relative to drug discontinuation or hospitalization for correction of clotting disorders is required.
What specific complications can occur during transthoracic lung biopsy?
According to the cited sources, transthoracic lung biopsy carries a confirmed risk of pneumothorax.
- During CT-guided lung biopsy, the use of a coaxial technique minimizes the number of pleural punctures and reliably reduces the risk of pneumothorax.
- In the clinical example of a lung biopsy, a CT-guided coaxial system makes it possible to obtain multiple biopsy samples with only a single pleural puncture.
Additionally, the coaxial technique as a whole is noted to theoretically reduce the risk of implantational metastasis along the puncture tract (track seeding).
To remember the difference between needles: FNA (Fine-Needle) — Fine/Filigree (cytology, thin, minimally invasive). Core — Chunky (histology, thick core, tissue architecture).
Class and exam questions
What is the essence and benefit of fusion imaging methods?
Fusion imaging allows pre-acquired CT, M/RI, or PET scans to be overlaid onto real-time ultrasound or fluoroscopy images. This helps precisely target lesions that are poorly visualized on the operating device but take up contrast or isotopes well on diagnostic scans.
What to do if a patient with coagulopathy cannot discontinue anticoagulants, but a liver biopsy is necessary?
In such cases, percutaneous access is contraindicated due to the high risk of bleeding. An alternative is transvascular biopsy (e.g., via the jugular or femoral vein) under fluoroscopic guidance.
Why is a stylet (mandrin) needed in fine-needle aspiration needles?
The stylet provides rigidity to the thin needle, preventing it from deflecting off course when advancing through dense tissues. Furthermore, it prevents contamination of the needle lumen with tissues lying along the path to the pathological lesion.
What else to study on this topic
- Pre-procedural risk assessment and discontinuation of anticoagulants
- Method of creating a cell block from FNA material
- Algorithm for using CT fluoroscopy in complex punctures
- Stereotactic breast biopsy for microcalcifications
- The role of Rapid On-Site Evaluation (ROSE) in a one-day clinic
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