Definition and Overview
Fine needle aspiration is a kind of biopsy that uses a thin needle (fine needle) to obtain cell samples for laboratory testing. Also used to drain abnormal fluid build-up in the body, it serves as both a diagnostic and a therapeutic tool.
Fine needle aspiration has several advantages over other forms of biopsy examinations. It is convenient for the patient since it is only an office procedure and is the least invasive method for biopsy. Patients are also able to save on costs as it is less expensive compared to excision biopsy or open biopsy.
Who Should Undergo and Expected Results
Fine needle aspiration can be used for many conditions, but it is best used for masses that are superficial, which means that they lie in the subcutaneous tissue below the skin.
The majority of fine needle aspirations are performed for masses located in the breast or the thyroid gland. However, the procedure can also be used to examine:
- Lymph nodes in various parts of the body, such as in the neck or the groin
- Masses in deeper organs, such as the liver and the lungs
- Fluid-filled masses, such as cysts or abscesses
- Seroma, which is an accumulation of fluid usually seen after an operation, at the incision site or where a mass or tissue has been removed
The procedure can be performed to:
- Diagnose the pathology of lumps or masses and determine if they are benign or malignant (cancerous)
- Diagnose infections and determine the specific organism causing them
- Evaluate the effect of treatment in patients who have already been diagnosed with a tumour
How is the Procedure Performed?
Fine needle aspiration is a simple outpatient procedure performed with or without imaging guidance. If the mass is easily palpable and accessible, imaging guidance is typically not necessary. If imaging guidance is used, the procedure is performed while the mass is being visualised using ultrasound or CT scan. In these cases, the procedure is typically performed by an interventional radiologist.
Whether performed with or without imaging guidance, the procedure is conducted as follows. The skin above the area where the needle will enter is cleaned aseptically. For deeper masses, a local anaesthetic may be given to numb the area. Once the mass is located, it is held in place before a syringe with a fine needle is inserted through the skin and subcutaneous tissue into the mass, and the syringe is aspirated. The vacuum in the syringe allows the cells or the fluid to be suctioned into the syringe. This may be repeated several times to ensure that an adequate amount of tissue is obtained for examination. Some experts recommend at least 5 to 6 passes of the needle through the mass. After the needle has been removed, the aspiration site is covered with a small gauze.
The aspirated material is then placed on a glass slide. Another glass slide is placed on top of the first, and the specimen is smeared. The smears are then fixed using alcohol or other stains and left to dry.
The slide is then sent to the laboratory for review under a microscopic and histopathologic examination. In some cases, the specimen is sent immediately to pathology to determine adequacy of the sample. Immunohistochemical staining, which determines the reactivity of the aspirated cells to different stains, may also be performed in the laboratory. When fluid is aspirated from the mass, it may also be sent for other examinations, such as gram stain and culture.
Possible Risks and Complications
Fine needle aspiration is generally a safe procedure. There are only minimal complications associated, and if these do occur, they are usually mild and resolve on their own.
The complications of the procedure usually depend on the organ being aspirated and the tissues surrounding it. For example, a fine needle aspiration biopsy of the liver may result in bile leaks on rare occasions.
Meanwhile, the usual complications include:
- Minimal bleeding
- Small bruises at the site of aspiration
- Mild inflammation and soreness
Also, the procedure can produce false negative results. Since only a thin needle is used, there is a risk that the diseased cells may be missed, and the examination will show normal results. This is especially true for small masses, and for cystic lesions containing acellular material. This risk can be minimised by performing several passes of the needle and using imaging guidance during the procedure. If there is failure to establish the diagnosis, a repeat fine needle aspiration or an excision biopsy may have to be performed.
Salgarelli AC, Cappare P, Bellini P, Collini M. Usefulness of fine-needle aspiration in parotid diagnostics. Oral Maxillofac Surg. 2009 Dec. 13(4):185-90.
Lastra RR, Pramick MR, Nakashima MO, Weinstein GS, Montone KT, Livolsi VA. Adequacy of fine-needle aspiration specimens for human papillomavirus infection molecular testing in head and neck squamous cell carcinoma. Cytojournal. 2013. 10:21.