Fine-needle aspiration cytology or FNAC is a diagnostic procedure used to investigate lumps or swellings. In this technique, a thin, hollow needle is inserted into the swelling for sampling of cells and tissue fragments. The material thus obtained is smeared on a glass slide, stained with specific chemicals, and then examined under a microscope.
Fine needle aspiration cytology has several advantages. They are extremely safe, minor surgical procedures. The technique is minimally invasive, requires no hospitalization and is inexpensive. It can be performed as an office procedure, in outpatient departments and in radiology theaters. It is also highly suitable in debilitated patients. Even the results are obtained in a short time.
Often, a major surgical (excisional or open) biopsy can be avoided by performing a fine needle aspiration cytology.
This procedure is widely used as first line treatment in the diagnosis of suspected cancer and inflammatory/ infectious conditions.
A needle aspiration is safer and less traumatic than an open surgical biopsy, and significant complications are usually rare.
Applications of Fine Needle Aspiration Cytology
Fine needle aspirations are often performed on a suspicious swelling or a lump to diagnose the underlying cause or if an abnormality is detected on an imaging test such as X-ray, ultrasound or mammography.
Most common sites which can be targeted include breast lumps, lymphnodes or other swellings of neck, axilla, groins, thyroid, etc.
Any swelling or abnormal mass arising at any part of the body may be subjected to FNAC to know the exact cause or underlying cause such as acute or chronic infections, benign tumors, cancers, etc.
In addition, for known tumors, the procedure is undertaken to assess the effect of treatment or recurrence or to obtain tissue for special and advanced studies.
FNAC is the main method used for chorionic villus sampling, and sampling of other body fluids. The information obtained by FNAC may be of decisive importance in the planning of medical treatment, surgery, radiotherapy, chemotherapy, etc.
When the lump can be felt or seen superficially, the biopsy is usually performed by a pathologist. In this case, the procedure is usually short and simple.
If the swelling is not felt or is not visible to naked eye, then it may be performed under radiological guidance using ultrasound, CT scan or endoscopic ultrasound. In this case, the procedure may require more extensive preparation and is time-consuming. These radiological tools help in guiding and placement of the needle within the lesion or swelling.
Radiological imaging not only provides accurate assessment of the location of the lesion but also its relations to other structures. Ultrasound needle guidance may also help representative sampling of palpable superficial lesions. For example, in case of predominantly cystic thyroid swellings, imaging helps to locate the small solid part of the swelling which must be sampled to provide the true diagnosis.
Preparation for FNAC
No specific or elaborate preparation is necessary for the procedure. Blood clotting profile may be checked in suspected patients. Vital signs including blood pressure and pulse rate may be monitored prior to the procedure. Very anxious patients, children or non-cooperative patients may be given anxiolytic drugs or sedation, if required. A brief clinical history regarding the duration of the presence of lump, how the patient became aware of its presence, any change in size, associated symptoms like pain or fever, etc should be undertaken in all patients.
Procedure of FNAC
The skin above the area of the swelling is swabbed with an antiseptic solution. The area may be numbed with a local anesthetic, although this is often not necessary. After locating the mass by palpation, it is held and fixed with one hand.
Using the other hand, a special fine needle (usually 22-24 G in thickness) is inserted into the swelling and withdrawn several times in different directions. This provides mild trauma which is required to dissociate the cells from the surrounding tissue. The procedure may be carried out using a special FNAC handle.
Aspiration or non-aspiartion techniques can be carried out depending upon the pathologist’s preference and the organ to be targeted. For example FNAC from thyroid are better done using a non aspiration technique since it leads to lesser bleeding. The cells thus dissociated are aspirated into the hub of the needle. The material so obtained is ejected onto clean glass slides. Then using another slide, this material is smeared onto the first glass slide to obtain an evenly spread thin smear.
Sometimes the procedure may have to be performed twice or several times to ensure that the swelling has been adequately sampled or to provide enough material for performing any special tests including immunocytochemistry, cytogenetics and molecular tests, if required. Each such procedure takes about 10 -‐ 20 seconds. The whole procedure from start to finish usually takes no more than 5 to 10 minutes.
Usually no post-operative care is needed. Mild pain relieving may be required in few patients. Major complications due to fine needle aspiration are not very common.
Infection are rare and can be treated by antibiotics.
Complications of FNAC Procedure
Bleeding is the most common complication of this procedure. A slight bruise may appear at the site of aspiration. If a lung or kidney aspiration has been performed, one can expect a small amount of blood in sputum or urine after the procedure. However only minimal bleeding should occur normally and bleeding should stop after some time. If more bleeding occurs for a prolonged period, the patient should be monitored till it stops completely. In very rare instance, surgical intervention may be required to control massive bleeding and compression of nearby organs.
Complications usually depend upon the body part on which FNAC is performed. FNAC from lungs or upper abdomen may result in pneumothorax (collection of air between chest wall and lung resulting in collapse of the lung).
Usually, this pneumothorax is mild and resolves on its own without treatment. Few patients may develop severe pneumothorax to require hospitalization and chest tube insertion. FNAC from liver may cause bile to leak into surrounding tissue. Injury to pancreas may occur after aspiration in the region of pancreas resulting in pancreatitis (inflammation of the pancreas).
Extremely rarely, deaths have been reported from FNAC . Such complications are extremely rare in view of the large number of uncomplicated FNACs performed routinely with close monitoring of patients.
Some concerns have been raised about the possibility of cancer cells being spread along the needle track at the site of FNAC. However this risk is extremely low when fine needles of 22 gauge or less are used.
Interpretations and Results of FNAC
The results can be broadly grouped into 3 categories:
Clearly benign (not cancererous)
This includes infectious, inflammatory and benign tumours. Depending upon the specific situation, patient may be provided medical treatment including antibiotics. In case of benign tumours, the patient may be given an option of surgical removal of the swelling or no further treatment.
Clearly malignant (cancerous)
This diagnosis requires immediate treatment.
A definitive specific diagnosis may not be possible by FNACin a proportion of cases. In such cases, a repeat FNAC, or surgical biopsy may be carried out to establish a definitive diagnosis.
Limitations of FNAC
Like any other procedure or investigation, this technique has certain inherent limitations.
Firstly, results and accuracy are highly dependent on the quality of samples and smears. Appropriate training and experience is essential to consistently achieve optimal material for diagnosis. Hence the procedure should only be carried out by an experienced pathologist.
Secondly, many diseases are heterogeneous, and the tiny sample obtained with a fine needle may not be representative of the whole swelling. Multiple passes can reduce this sampling bias to some extent.
Thirdly, some lesions are recognized mainly on the specific microarchitectural pattern, which is not usually represented in cytological preparations. Aspiration cytology should not be considered a substitute for conventional surgical histopathology / biopsy.
It should rather be regarded as a preoperative/ pretreatment investigation of disease process, in combination with clinical, radiological and other laboratory data.