Fine Needle Aspiration Cytology

Dr. Topesh Patle

Introduction

  1. Fine Needle Aspiration Cytology (FNAC) is a simple medical test used to collect cells from a lump, swelling, or abnormal tissue using a thin needle.
  2. The main principle of FNAC is to collect cells from the affected area and examine them under a microscope to identify any abnormal changes.
  3. FNAC helps doctors determine whether a lump is likely to be benign (non-cancerous), malignant (cancerous), or related to inflammation or infection.
  4. It is commonly used to examine lumps in the thyroid gland, breast, lymph nodes, salivary glands, and other parts of the body.
  5. During the procedure, the collected cells are placed on glass slides, stained with suitable dyes, and examined under a microscope.
  6. The cells are studied for their size, shape, arrangement, nuclear appearance, and other features that may help identify the disease.
  7. FNAC is a quick and relatively inexpensive procedure. It usually causes less discomfort and tissue damage than surgical biopsy.
  8. Although FNAC is useful for diagnosing many diseases, some cases require additional tests or a tissue biopsy to confirm the diagnosis.

Principles

The principle of FNAC is based on the collection of cellular material from a lesion using a fine needle.

The aspirated cells are transferred onto glass slides, processed, stained, and examined microscopically.

  • A suspicious lesion is identified by clinical examination or imaging.
  • A fine needle is introduced into the lesion.
  • Cellular material is obtained through aspiration or needle movement, depending on the technique.
  • The collected material is transferred onto glass slides.
  • Smears are prepared and appropriately fixed or air-dried.
  • The slides are stained using suitable cytological stains.
  • The cells are examined under a microscope.
  • The cytological findings are correlated with the clinical and imaging findings.

Types of Fine Needle Aspiration Cytology

FNAC can be classified according to the method of sampling and the type of lesion being investigated.

Aspiration FNAC

  • In aspiration FNAC, negative pressure is applied using a syringe to help collect cellular material.

Characteristics:

  • A fine needle is introduced into the lesion.
  • A syringe is used to generate suction.
  • Cellular material enters the needle.
  • The aspirated material is transferred onto slides for examination.

Non-Aspiration FNAC

  • Non-aspiration FNAC is also known as the capillary sampling technique.

Characteristics:

  • A fine needle is introduced into the lesion.
  • No syringe suction is applied during sampling.
  • Cellular material enters the needle through capillary action and needle movement.
  • The technique may be useful for selected highly vascular or delicate lesions, depending on the clinical circumstances and operator experience.

Image-Guided FNAC

  • Image-guided FNAC uses imaging techniques to direct the needle into a target lesion.

Common imaging methods include:

  • Ultrasonography.
  • Computed tomography (CT), in selected cases.
  • Other imaging guidance methods, depending on the location of the lesion.

Advantages:

  1. Helps target deep-seated lesions.
  2. Improves sampling accuracy in selected cases.
  3. Helps sample small or difficult-to-palpate lesions.
  4. Reduces the likelihood of sampling the wrong area.

Specimens

FNAC can be performed on lesions involving several organs.

Organ or site Common clinical indication Diagnostic purpose
Thyroid gland Thyroid nodule Evaluation of benign, suspicious, or malignant cytological features
Breast Palpable lump Assessment of selected breast lesions
Lymph nodes Lymphadenopathy Investigation of reactive, infectious, and neoplastic conditions
Salivary glands Parotid or other salivary gland mass Evaluation of salivary gland lesions
Skin and subcutaneous tissue Superficial swelling Investigation of selected cysts, inflammatory lesions, and tumors
Soft tissues Soft-tissue mass Preliminary evaluation of selected lesions
Lung Pulmonary mass Sampling of selected lesions, commonly with imaging guidance
Liver Focal hepatic lesion Evaluation of selected focal lesions
Other organs Clinically or radiologically identified lesions Investigation according to the clinical indication

The suitability of FNAC depends on the lesion’s location, suspected diagnosis, imaging findings, and the need for tissue architecture or additional testing.

Material Requirements

To ensure the success of the FNAC procedure, specific materials are required:

  • Sterile fine needle of an appropriate gauge.
  • Syringe, when aspiration is required.
  • Needle holder or aspiration device, if indicated.
  • Clean glass slides.
  • Slide labels and specimen identification materials.
  • Appropriate fixative.
  • Cytological stains.
  • Gloves and other personal protective equipment.
  • Antiseptic solution.
  • Gauze or cotton swabs.
  • Specimen containers and transport materials, when required.
  • Ultrasound or other imaging equipment for image-guided procedures.

Procedures

The FNAC procedure involves several key steps to ensure accurate sampling and diagnosis:

Patient Preparation

  1. Confirm the patient’s identity.
  2. Review the clinical history and relevant imaging findings.
  3. Identify the target lesion.
  4. Explain the procedure and obtain appropriate consent.
  5. Assess relevant bleeding risks and medications when indicated.
  6. Position the patient appropriately.
  7. Prepare the sampling site using an appropriate antiseptic technique.

 

Needle Insertion and Sampling

  1. Select a suitable needle and sampling device.
  2. Stabilize the lesion when appropriate.
  3. Introduce the needle into the target lesion.
  4. Obtain cellular material using the selected aspiration or non-aspiration technique.
  5. Avoid unnecessary movement and tissue trauma.
  6. Withdraw the needle safely after sampling.
  7. Apply local pressure when appropriate to minimize bleeding.

The exact procedure varies according to the anatomical site and whether imaging guidance is required.

Preparation of Cytological Smears

  1. Transfer the collected material onto clean, labeled glass slides.
  2. Prepare thin, uniform smears using an appropriate spreading technique.
  3. Avoid excessive pressure that could damage the cells.
  4. Prepare additional smears when sufficient material is available.
  5. Fix some smears immediately in alcohol when required for Papanicolaou staining.
  6. Allow other smears to air-dry when they are intended for Romanowsky-type stains.
  7. Place any additional material into an appropriate transport medium when required for ancillary investigations.

Staining of Smears

Commonly used stains include:

1. Papanicolaou Stain

  • A multichromatic cytological stain.
  • Provides detailed nuclear features.
  • Helps evaluate cellular morphology.
  • Commonly used for alcohol-fixed smears.

2. May-Grünwald-Giemsa (MGG) Stain

  • A Romanowsky-type stain.
  • Commonly used for air-dried cytological smears.
  • Helps demonstrate cytoplasmic features and background material.
  • Useful for examining inflammatory cells and many other cellular patterns.

3. Hematoxylin and Eosin (H&E) Stain

  • Primarily associated with histopathology.
  • May be used in selected cytological preparations according to laboratory protocols.
  • Is not the principal routine stain for most conventional FNAC smears.

4. Special Stains

  • May be used when a specific organism, substance, or cellular component needs further evaluation.
  • The choice depends on the suspected diagnosis.

Microscopic Examination

  • The prepared slides are examined under a microscope.

The cytopathologist assesses:

  1. Specimen adequacy.
  2. Cellular arrangement.
  3. Cell size and shape.
  4. Nuclear size and morphology.
  5. Nuclear-to-cytoplasmic ratio.
  6. Chromatin pattern.
  7. Nucleoli.
  8. Cytoplasmic characteristics.
  9. Background material.
  10. Evidence of inflammation, necrosis, or other relevant findings.

The findings are interpreted alongside clinical information and imaging results.

Cytological Features Evaluated in FNAC

Microscopic examination focuses on several cellular and background characteristics.

Cellular Arrangement

Cells may appear as:

  • Isolated cells.
  • Small cellular groups.
  • Cohesive sheets.
  • Clusters or three-dimensional groups.
  • Papillary or other architectural fragments.

The arrangement varies with the type of lesion and tissue of origin.

Nuclear Features

Important nuclear features include:

  • Nuclear size.
  • Nuclear shape.
  • Nuclear membrane irregularity.
  • Chromatin distribution.
  • Nucleolar prominence.
  • Nuclear pleomorphism.

These features may help distinguish different types of lesions.

Cytoplasmic Features

The cytoplasm is evaluated for:

  • Amount of cytoplasm.
  • Shape and boundaries.
  • Staining characteristics.
  • Vacuoles or granules.
  • Inclusions or other distinctive features.

Background Material

The background may contain:

  • Blood.
  • Inflammatory cells.
  • Necrotic material.
  • Colloid.
  • Mucin.
  • Proteinaceous material.
  • Other substances associated with the sampled lesion.

The significance of these findings depends on the anatomical site and clinical context.

Interpretation and Reporting

FNAC reports describe the adequacy of the specimen and the observed cytological findings.

Common Diagnostic Categories

1. Inadequate or Nondiagnostic

  • The specimen contains insufficient material or lacks the necessary diagnostic features.
  • A repeat procedure or alternative investigation may be required.

2. Benign

  • The cytological findings support a nonmalignant process.
  • Clinical and imaging correlation remains important.

3. Atypical or Indeterminate

  • The findings are not sufficiently specific for a definitive benign or malignant classification.
  • Additional investigations may be necessary.

4. Suspicious for Malignancy

  • The specimen contains features concerning for malignancy.
  • Further assessment and confirmatory investigation are generally required.

5. Malignant

  • The cytological findings support a malignant lesion when diagnostic criteria are met.
  • Additional testing may be needed to determine the exact tumor type or guide treatment.

These categories are general descriptions. Organ-specific reporting systems may use different terminology and diagnostic categories.

Importance of Clinical Correlation

FNAC findings should be interpreted alongside:

  • Clinical examination.
  • Medical history.
  • Imaging findings.
  • Laboratory investigations.
  • Previous biopsy results, when available.
  • Additional cytological, histological, or molecular studies when indicated.

A benign cytological result does not automatically exclude malignancy if the clinical or imaging findings remain suspicious.

Advantages

The major advantages of Fine Needle Aspiration Cytology include:

  1. Minimally invasive: Usually requires only a fine needle.
  2. Rapid procedure: Sampling is often completed within a short period.
  3. Relatively inexpensive: Generally less costly than many surgical diagnostic procedures.
  4. Limited tissue trauma: Usually causes less tissue disruption than surgical biopsy.
  5. Outpatient suitability: Many superficial lesions can be sampled in an outpatient setting.
  6. Repeatability: Sampling can often be repeated when necessary.
  7. Wide applicability: Can be used to investigate lesions in several organs.
  8. Rapid preliminary assessment: Results may be available relatively quickly, depending on laboratory facilities.
  9. Ancillary testing: Suitable material may be used for selected immunocytochemical or molecular investigations.

Limitations 

Despite its advantages, FNAC has several limitations.

Sampling Error

  • The needle may miss the representative portion of a lesion.
  • Some lesions contain heterogeneous cellular populations.
  • Inadequate sampling may produce misleading results.

Inadequate Specimen

  • The sample may contain too few diagnostic cells.
  • Blood or necrotic material may obscure cellular details.
  • Repeat sampling may be required.

Limited Tissue Architecture

  • FNAC collects cells rather than an intact tissue core.
  • It generally cannot demonstrate the complete relationship between cells and surrounding tissue.
  • Some diagnoses require histopathological examination.

Difficulty in Certain Diagnoses

  • Some benign and malignant lesions have overlapping cytological features.
  • Certain tumors require evaluation of tissue invasion or architecture.
  • Additional investigations may be needed to establish the diagnosis.

Operator Dependence

  • Sampling quality depends on the operator’s skill.
  • Correct targeting is essential.
  • Preparation and interpretation require appropriate training.

Need for Confirmatory Testing

  • Some lesions require core needle biopsy or surgical biopsy.
  • Additional tests may be necessary for tumor classification.
  • Cytological findings must be correlated with the overall clinical picture.

Complications and Safety Considerations

FNAC is generally well tolerated, but complications can occur.

Possible Complications

  1. Mild pain or discomfort.
  2. Minor bleeding.
  3. Bruising or hematoma.
  4. Local infection, which is uncommon.
  5. Inadequate sampling requiring repeat aspiration.
  6. Rare complications related to the anatomical site or sampling procedure.

Safety Measures

  • Follow appropriate aseptic precautions.
  • Use sterile, suitable equipment.
  • Review relevant bleeding risks.
  • Apply appropriate post-procedure care.
  • Use imaging guidance when clinically indicated.
  • Ensure correct specimen labeling and transport.
  • Follow site-specific clinical protocols.

FNAC Versus Biopsy

FNAC and tissue biopsy are both used to investigate abnormal lesions, but they differ in the material collected.

Feature FNAC Core Needle Biopsy
Full form Fine Needle Aspiration Cytology Core Needle Biopsy
Sample obtained Cells and small cellular groups Cylinders of tissue
Main examination Cytology Histopathology
Tissue architecture Generally not preserved Partially preserved
Invasiveness Usually minimally invasive Usually more invasive than FNAC
Specimen preparation Cytological smears and other suitable preparations Tissue processing and histological sections
Assessment of tissue invasion Generally limited Often possible, depending on the sample
Ancillary testing Possible with suitable material Possible with suitable tissue
Common limitation Sampling and architectural limitations Sampling limitations and procedural risks

Important: Neither method is universally superior. The appropriate procedure depends on the lesion, the suspected diagnosis, and the information required for clinical management.

Clinical Applications 

FNAC is used in several areas of diagnostic medicine.

Thyroid Lesions

  • Evaluation of selected thyroid nodules.
  • Identification of cytological features associated with benign or malignant lesions.
  • Guidance for further investigation and management.
  • Correlation with thyroid ultrasound findings.

Breast Lesions

  • Investigation of selected palpable breast lumps.
  • Assessment of cystic lesions.
  • Preliminary evaluation of certain neoplastic lesions.
  • Correlation with clinical examination and breast imaging.

FNAC is not always sufficient for definitive diagnosis, and core needle biopsy may be preferred when tissue architecture or tumor biomarkers are required.

Lymph Node Lesions

  • Investigation of enlarged lymph nodes.
  • Assessment of reactive lymphadenopathy.
  • Evaluation of selected infectious and inflammatory conditions.
  • Detection of metastatic carcinoma in appropriate cases.

Some lymphomas require core or excisional biopsy for accurate classification.

Salivary Gland Lesions

  • Evaluation of parotid and other salivary gland masses.
  • Differentiation of selected non-neoplastic and neoplastic lesions.
  • Assistance in clinical decision-making.

Soft-Tissue Lesions

  • Preliminary evaluation of selected superficial masses.
  • Investigation of some cystic and inflammatory lesions.
  • Assessment of certain soft-tissue tumors.

Core biopsy may be necessary for definitive tumor classification.

Deep-Seated Lesions

Image-guided FNAC may be used to investigate selected lesions involving:

  • Lung.
  • Liver.
  • Pancreas.
  • Mediastinum.
  • Other deep-seated organs.

The choice of sampling method depends on the anatomical location, suspected disease, and availability of imaging guidance.