What is FNAC needles size in FNAC and what is tru cut biopsy
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Here is a detailed answer drawn from authoritative surgical textbooks:
FNAC - Fine Needle Aspiration Cytology
Needle Size
- 22 or 23 gauge needle (most commonly used) - S Das Manual on Clinical Surgery, 13th Ed.
- In breast FNAC specifically: 22-gauge needle, 1.5 inches long, attached to a 10 mL syringe - Schwartz's Principles of Surgery, 11th Ed.
- The 23-gauge (blue hub) needle on a 10 mL syringe is standard for breast lumps - Pye's Surgical Handicraft, 22nd Ed.
What FNAC Does
- A fine needle is fitted to a tight-fitting syringe (typically 10-20 mL)
- The needle is inserted into the swelling; suction is applied while moving the needle back and forth within the mass
- Once cellular material appears at the hub, suction is released and needle withdrawn
- The aspirated cells (NOT a tissue core) are smeared onto a glass slide
- Slides are fixed with absolute alcohol and stained using the Papanicolaou technique (air-dried preparations are also made)
- It provides cytological (cell-level) diagnosis only - tissue architecture is NOT preserved
Tru-Cut Biopsy (Core Needle Biopsy)
What It Is
Tru-Cut is a brand/type of core needle biopsy - the Travenol Tru-Cut needle is the classic instrument. It is a hollow cutting needle that retrieves a core (cylinder) of intact tissue for histological examination, unlike FNAC which only gets cells.
Needle Size
- 14 gauge needle for palpable breast masses (Tru-Cut needle) - Schwartz's Principles of Surgery
- 16 gauge for Tru-Cut liver biopsies (rare fragmentation, large core, 17-20 mm maximum core length) - Yamada's Gastroenterology
- Vacuum-assisted core biopsy devices use 8-10 gauge needles (larger = more tissue)
Mechanism
- A hollow needle is introduced into the swelling
- A core of tissue is cut and withdrawn for histopathological examination
- Classic uses: Travenol Tru-Cut needle for prostate (via perineum), Vim-Silverman needle for liver
- Automated spring-loaded "biopsy guns" are now commonly used for prostate, breast, kidney
Key Comparison
| Feature | FNAC | Tru-Cut / Core Biopsy |
|---|---|---|
| Needle gauge | 22-23 G (fine) | 14-16 G (large bore) |
| Yield | Individual cells | Core of intact tissue |
| Analysis | Cytology | Histopathology |
| Architecture preserved? | No | Yes |
| Invasiveness | Minimal | Moderate |
| Can detect invasion? | No | Yes |
| Main use | Lymph nodes, thyroid, breast | Breast, liver, prostate, kidney |
As stated in Harrison's Principles of Internal Medicine (2025): for lymphoma diagnosis, "a histologic (tissue) diagnosis is essential and should be obtained with a Tru-Cut biopsy needle - fine needle aspiration cytology is an acceptable but less preferred alternative" because tissue architecture is needed to classify lymphoma subtypes.
Maximum dosage of local anaesthetic used in lipoma surgery and mechanism of action and duration of action
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I have comprehensive information from the textbooks. Here is the full answer:
Local Anaesthesia in Lipoma Surgery
Lipoma excision is almost always performed under local infiltration anaesthesia. The drug of choice is lidocaine (lignocaine).
Maximum Dosage
From Bailey & Love's Short Practice of Surgery, 28th Edition (Table 23.2):
| Drug | Max Dose (Plain) | Max Dose (with Adrenaline) |
|---|---|---|
| Lidocaine (Lignocaine) | 3 mg/kg | 7 mg/kg |
| Bupivacaine | 2 mg/kg | - |
| Prilocaine | 6 mg/kg | 9 mg/kg |
| Ropivacaine | 3-4 mg/kg | - |
| Levobupivacaine | 2 mg/kg | - |
From Pye's Surgical Handicraft, 22nd Edition (practical numbers for a 70 kg adult):
| Preparation | Max Total Dose |
|---|---|
| Plain lignocaine | 200 mg (~3 mg/kg) |
| Lignocaine + adrenaline 1:200,000 | 500 mg (~7 mg/kg) |
Volume guide for infiltration (plain lignocaine):
- 0.5% (5 mg/mL) → max 40 mL
- 1% (10 mg/mL) → max 20 mL
- 2% (20 mg/mL) → max 10 mL
Volume guide (with adrenaline 1:200,000):
- 0.5% → max 100 mL
- 1% → max 50 mL
- 2% → max 25 mL
For lipoma surgery, 1% lignocaine with adrenaline 1:200,000 is the practical choice - it provides adequate anaesthesia, a dry field via vasoconstriction, and a safe volume margin. Wait at least 5 minutes after injection before incision to allow vasoconstriction to work.
Mechanism of Action
Local anaesthetics are membrane-stabilising agents that work by:
- Penetrating the nerve membrane - the drug (as a lipid-soluble free base) diffuses through the nerve cell membrane
- Blocking voltage-gated Na⁺ channels - once inside, the ionised (charged) form binds to receptors on the inner face of sodium channels
- Preventing depolarisation - Na⁺ influx is blocked, so the action potential cannot be generated or propagated
- Reversible block - conduction is blocked reversibly; smaller, unmyelinated C-fibres (pain, temperature) are blocked first, followed by larger myelinated A-fibres (touch, pressure, motor)
Key point: Local anaesthetics do NOT affect resting membrane potential or threshold - they simply prevent the membrane from depolarising in response to a stimulus.
Why adrenaline helps:
- Causes local vasoconstriction, reducing systemic absorption of the local anaesthetic
- This prolongs duration of action and increases the safe maximum dose (by keeping the drug at the site longer)
- Adrenaline is contraindicated in end-arterial sites (fingers, toes, tip of nose, ear pinna, penis) due to risk of ischaemia
Duration of Action
| Drug | Duration (Plain) | Duration (With Adrenaline) |
|---|---|---|
| Lignocaine | 1-2 hours | 2-4 hours |
| Bupivacaine | 4-8 hours | Up to 12 hours |
| Prilocaine | 1-2 hours | 2-4 hours |
| Ropivacaine | 4-8 hours | - |
Lignocaine has a rapid onset (2-5 minutes) and intermediate duration, making it ideal for outpatient lipoma excision.
Caution - Reduce Max Dose In:
- Low body weight / children
- Elderly or debilitated patients
- Hepatic disease (lignocaine is metabolised in the liver)
- Renal impairment
- Epilepsy
- Heart block
Signs of lignocaine toxicity: Anxiety, excitement, drowsiness, convulsions, respiratory arrest (CNS toxicity), followed by hypotension, bradycardia, heart block (cardiac toxicity). - Pye's Surgical Handicraft
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