Fine Needle Aspirate
Fine needle aspirates (FNA) are useful for gaining cellular samples from tissues. This procedure can be performed directly on superficial lesions (e.g., skin/subcutaneous masses, peripheral lymph nodes). Ultrasound guidance can be used to perform FNA on internal organs or structures. FNA sometimes does not yield any material (or insufficient material for a diagnosis), and in these cases, biopsy is required.
Summary of the Procedure:
| Indications | Diagnosis of cause of lymphadenopathy or a mass. |
| Limitations | May not be able to distinguish lymph node hyperplasia from lymphoma.
Cannot characterize tissue architecture. Cannot distinguish lipoma from subcutaneous fat. Cells in mass may not exfoliate. |
| Complications | Uncommon.
Hemorrhage and sharp trauma to surrounding tissues (including internal organs if biopsying thoracic or abdominal mass). Degranulation of mast cell tumor. Low risk of tracking neoplastic cells through the needle tract. |
| Contraindications | Bleeding disorder for biopsy of thoracic or abdominal mass. |
| Supplies/instruments | 22 ga needle
3 to 12 mL syringe. (Premedication with diphenhydramine recommended when aspirating masses that could be mast cell tumors). |
| Position | Depends on mass. |
| Restraint | Typically no sedation required; mild sedation may be necessary for some individuals. |
Details of the Procedure (for direct aspirates of superficial structures):
- Cleanse (often used with lymph nodes and cutaneous masses) or surgically prepare entry site.
- Immobilize lymph node / mass between fingers of one hand.
- With other hand insert needle into mass several times. Withdraw needle part way, redirect, insert again up to three times. Some clinicians will also twist the needle each time after inserting it.
4. Withdraw needle, attach to 3 to 12 mL syringe with plunger drawn, expel sample onto slide. Make a smear using same technique as blood smear.
Alternative FNA technique:
- Attach needle to 3 to 12 mL syringe, insert needle into mass, draw back on plunger.
- Withdraw needle part way, redirect, insert and re-aspirate.
- Release suction prior to withdrawing needle.
- Detach needle from syringe, withdraw plunger, and expel sample onto slide.
- This technique can rupture cells and compromise diagnosis, so it is usually only used when the redirection technique does not yield a sample.