Fine Needle Aspiration Cytology

FNAC Fundamentals - Point & Shoot

• Definition: Diagnostic procedure using a fine needle to aspirate cells from a lesion for microscopic examination.
• Principle: Cellular material obtained by suction through a needle, smeared on a slide, stained, and evaluated.
• Advantages: 📌 S.A.F.E.R - Simple, Accurate, Fast, Economical, Reliable. Minimally invasive.
• Disadvantages: Sampling error (may miss lesion), no tissue architecture, operator dependent.
• Indications: Palpable lesions (thyroid, breast, lymph nodes), image-guided for deep lesions (lung, liver).
• Contraindications: Severe bleeding diathesis, uncooperative patient, overlying infection (relative).

⭐ FNAC is a rapid, minimally invasive, and cost-effective diagnostic tool, often the first line of investigation for palpable masses.

FNAC Workflow - Poke, Smear, Stain

1. Poke (Aspiration):

• Needle: Typically 22-25 gauge; length varies.
• Syringe: 10-20 ml, often pistol grip for single-hand operation.
• Techniques:
  • Suction: using syringe for negative pressure.
  • Non-aspiration (Zajdela/capillary technique): uses capillary action of fine needle.

2. Smear (Slide Preparation):

• Expel material onto slide.
• Methods:
  • Direct smear.
  • Pull-apart/slide-over-slide (common).
  • Crush: for cellular/fragmented material.

3. Stain (Fixation & Staining):

• Fixation & Stains:
  • Air-drying: For Romanowsky (e.g., MGG, Giemsa); highlights cytoplasm, matrix.
  • Wet fixation: 95% ethanol for Papanicolaou (Pap - nuclear detail, keratin) & H&E (general morphology).

⭐ The choice of fixation and staining (Air-dried/Romanowsky vs. Alcohol-fixed/Pap) depends on the suspected diagnosis and institutional preference, each highlighting different cellular features.

FNAC Procedure Flowchart:

Cytological Interpretation - Decoding the Cells

• Specimen Adequacy:
  • Sufficient cellularity
  • Presence of diagnostic cells
  • Absence of obscuring elements (blood, clot)
• General Cytomorphological Features:
  • Background: Clean, bloody, inflammatory, necrotic
  • Arrangement: Clusters, sheets, acini, papillary, single cells
  • Cell: Size, shape
  • Nucleus: N:C ratio, chromatin (fine/coarse), membrane (smooth/irregular), nucleoli (inconspicuous/prominent)
  • Cytoplasm: Amount, color, granules, vacuoles, inclusions
• Criteria of Malignancy: 📌 Mnemonic: Ugly Nuclei
  • Anisokaryosis/Pleomorphism
  • Hyperchromasia
  • Irregular nuclear contours
  • Prominent/multiple nucleoli
  • ↑ N:C ratio
  • Abnormal mitoses
• Reporting Systems:
  • Bethesda (Thyroid)
  • Milan (Salivary Gland)
  • IAC Yokohama (Breast)
  • Paris (Urine)

⭐ Accurate interpretation requires assessing both individual cell morphology and the overall architectural pattern of cell groups, alongside clinical context.

Organ-Specific FNAC - Target Practice

• Thyroid:
  • Hashimoto's: Lymphocytes, Hürthle cells.
  • Papillary Ca: Nuclear grooves, intranuclear inclusions, psammoma bodies.
  • General: Colloid, follicular cells.
• Lymph Node:
  • Reactive Hyperplasia: Polymorphic lymphoid population.
  • TB Lymphadenitis: Epithelioid granulomas, Langhans giant cells, caseous necrosis.
  • Metastasis: Foreign cells.
• Breast:
  • Fibroadenoma: Staghorn clusters of ductal cells, bipolar naked nuclei.
  • Ductal Carcinoma: Cellular, discohesive malignant cells, pleomorphism.
• Salivary Gland:
  • Pleomorphic Adenoma: Chondromyxoid stroma, epithelial/myoepithelial cells.

⭐ In thyroid FNAC, nuclear features like grooves, inclusions, and powdery chromatin are key to diagnosing Papillary Thyroid Carcinoma, even with scant cellularity.

High‑Yield Points - ⚡ Biggest Takeaways

• FNAC is a minimally invasive, cost-effective, and rapid diagnostic tool.
• Uses fine needles (typically 22-27 gauge) for cellular material aspiration.
• Key for evaluating palpable lesions: thyroid nodules, breast lumps, lymph nodes.
• Image guidance (USG/CT) is vital for non-palpable or deep-seated lesions.
• ROSE ensures sample adequacy, reducing need for repeat procedures.
• Effectively differentiates benign vs. malignant conditions, guiding management.
• Complications like hematoma are rare and generally minor.