Fine needle aspiration biopsy

Keywords: FNAB

Specimen:

Aspiration of material for cytological examination through a fine bore needle (approximately 23-25 gauge) can be performed from virtually any site. 

The technique is best performed by a trained cytopathologist who will also evaluate the smears. Other clinicians, such as surgeons and radiologists, frequently perform the technique after appropriate training and supervised experience, and may request attendance of laboratory staff to aid in smear preparation and indicate adequacy of material (especially during X-ray, CT or ultrasound guided aspiration).

Clinical information is essential.

Method:

Tissue is obtained following puncture of the lesion and careful movement of the tip of the needle within the lesion; gentle suction may be applied.

For superficial palpable lesions the needle may be moved back and forth with a fanning action providing wider sampling and cell dislodgement.

In most cases, the aspirated material remains in the needle (unless cystis fluid present), and is then expressed onto pre-labelled slides and smeared out rapidly, or expressed into fixative for liquid based cytology.

Care needs to be followed when expressing material onto slides in patients with suspected infection eg, Tuberculosis. This should be undertaken in a biohazard cabinet.

Both air-dried and 70-95% ethanol or commercial wet fixed smears are preferred, but may depend on the tissue being sampled and on the preference of the reporting pathologist.

Tissue remaining within the needle, or a repeat aspirate, may be washed out in a non-fixative solution and used for microbiological examination, cytocentrifuge preparations, hormone receptor evaluation, cell block preparation, immunohistochemistry, cytogenetics, molecular genetics, or EM (special fixative).

If there is clinical suspicion of lymphoma or reactive lymph node, material may also be sent for cell surface markers.

Application:

Fine needle aspiration biopsy is valuable in the diagnosis of superficial and readily accessible lesions eg, skin and breast. 

With organ imaging techniques, deeply situated organs can be sampled. 

The technique is used mainly in the primary diagnosis of neoplasia and for the assessment of disease recurrence. Infections and benign lesions are also readily evaluated.

Some neoplasms and well differentiated lesions may result in an abnormal but equivocal diagnosis requiring histological confirmation (eg, follicular neoplasms of thyroid, well differentiated hepatocellular carcinoma).

Interpretation:

Report by pathologist identifies the nature of the lesion sampled.

Reference:

Orell SR, Sterrett GF. Orell and Sterrett's Fine needle aspiration cytology. 5th ed. Churchill Livingstone 2011

Kini SR. Colour Atlas of Differential Diagnosis in Exfoliative and Aspiration Cytopathology. 2nd ed 2011. Lippincott Williams and Wilkins.