Fine Needle Aspiration

Anatomy and Physiology

While fine-needle aspiration can technically be used on essentially any region of the body, it is most commonly used to biopsy newly identified masses in the breast, the thyroid, suspicious lymph nodes, or suspicious skin masses.[2][3][4][5][6] The development of endoscopic ultrasound, as in conjunction with advanced endoscopes, means that pancreatic, gastrointestinal, esophageal, and tracheal pathology may be biopsied with a fine needle as well.[7][8][9][10] Finally, as imaging modalities become more advanced, CT-guided fine-needle biopsies can be taken of almost any region in the body.[11][12][13][14][15][16] In essence, all but the most inaccessible regions of the body are amenable to fine-needle aspiration.

Given the diverse array of anatomical structures that may be accessed by fine-needle aspiration, detailing the anatomical nuances of each is beyond the scope of this chapter; however, there are a few universal principles worth mentioning. The first is to plan any fine-needle aspiration so that it avoids any critical intervening structures or blood vessels; it is inappropriate to biopsy the liver through the gallbladder or the thyroid through an intervening artery, for example. Secondly, while fine-needle aspiration can be used to aspirate abscesses, particularly in cosmetically sensitive areas such as the breast, infected areas should otherwise be avoided as it will seed infectious material along the tract of the needle.[17] Finally, the healthcare provider performing the fine-needle aspiration should be intimately familiar with the anatomy of the area being investigated to minimize the risk of complications and give the highest chance of the biopsy giving the correct diagnosis.

Indications

Fine-needle aspiration is indicated in any situation where a tissue or fluid sample would aid in diagnosis or treatment. This can include determining the cell type of nonfunction thyroid nodules, suspicious skin masses, or suspicious breast masses. Fine-needle aspiration can investigate if there is malignancy contained within suspicious lymph nodes or new masses that may arise from any of the previously mentioned organs. In the setting of a known diagnosis, particularly with metastatic disease, fine-needle aspiration of suspicious lymph nodes or masses can be used to determine genetic or molecular markers that indicate the cancer is susceptible to specific chemotherapeutic or biologic treatments. Fine-needle aspiration may be used to aspirate the contents of an abscess to treat it when combined with antibiotics, and this treatment is used rather than the standard incision and drainage in cosmetically sensitive areas such as the breast, although data on its efficacy is mixed.[17] Finally, fine-needle aspiration may be used to remove fluid from a seroma if necessary. However, this is typically avoided since it presents the chance of potentially infecting an otherwise sterile fluid collection.[18]

Fine-needle aspiration is also an important triage in deep-seated lesions such as in lung, mediastinum, and abdominal organs, including pancreas and lymph nodes, especially in patients who are not fit for more invasive biopsy sampling.

Contraindications

Fine-needle aspiration is contraindicated in any situation where it would not alter management; for example, if a patient has a large, isolated, and symptomatic pancreatic mass, there is no need to biopsy it since it already mandates surgical excision and, if malignant, runs the risk of seeding the needle tract with cancer cells.[19] Fine-needle aspiration is also contraindicated if a safe biopsy window is unobtainable, although this is relatively rare given the small size of the needle. As previously mentioned, fine-needle aspiration is contraindicated in the setting of an infected field where it may introduce infectious material into a sterile space. Fine-needle aspiration is relatively contraindicated when there is a high degree of suspicion that cytology will not be sufficient to make the diagnosis and histology are needed; this is most commonly seen in the setting of suspected lymphoma. A few of the lesions which should not be attempted for fine-needle aspiration cytology (FNAC) include paraganglioma, hydatid cyst, and vascular neoplasms. An additional relative contraindication is if the patient is supratherapeutically anticoagulated or extremely coagulopathic. Once again, the small size of the fine needle used in this procedure generally ensures that even these patients have minimal bleeding risk and that any bleeding that does occur can be stopped with manual compression.

Equipment

Fine-needle aspiration requires a minimal amount of equipment. If the lesion to be biopsied is superficial, it will require just a small needle, an aspiration device such as a syringe, sterile gloves, and an antiseptic swab or wipe to sterilize the biopsy site. Local anesthesia, such as lidocaine, is typically not needed during the procedure as administering the anesthetic itself may cause more pain than the small-bore needle. If the lesion is within the abdominal cavity, it may undergo fine-needle aspiration with a specialized percutaneous or laparoscopic device. Fine-needle aspiration can also be performed via an endoscope or bronchoscope, again via a specialized device. In addition to the needle and aspiration device, appropriate material to maintain sterile technique is required. If the aspiration is to be image-guided, then imaging equipment such as an ultrasound will also be necessary.

Personnel

If the lesion is superficial, then a solo healthcare provider may perform the fine-needle aspiration by themself. As with many minor procedures, it may still be helpful to have an assistant available in case extra supplies or an extra set of hands become necessary.

If the procedure is to be performed laparoscopically, endoscopically, or percutaneously then the additional personal necessary to anesthetize and monitor the patient will also be required.

Preparation

If the area to be aspirated is superficial, then simply sterilizing the area before performing fine-needle aspiration is all that is necessary.

If the procedure is to be performed laparoscopically, endoscopically, or percutaneously then additional preparation is required as there would be for any procedure performed that way, including confirming the planned site and sedating or anesthetizing the patient.

Technique or Treatment

If the area to undergo fine-needle aspiration is superficial and palpable, then once the area is sterilized, simply inserting the needle into the lesion while gently aspirating is all that is necessary. If the lesion is not palpable, then ultrasound guidance should ensure an appropriate sample is taken. Even if the lesion is palpable, ultrasound can be useful to guide the needle. CT-guided fine-needle aspiration may be performed similarly except under CT guidance.

If the fine-needle aspiration is to be performed via endoscopy or bronchoscopy, the lesion may be aspirated through direct visualization or with the addition of ultrasound guidance. If the lesion is not visible, for example, if a paratracheal lymph node needs to be sampled, then an ultrasound will be necessary. This requires a specialized scope with an ultrasound probe attached as well as a device on the tip of the scope to deploy the needle. Still, the ultimate technique is the same: inserting the needle into the area under investigation while aspirating.

Complications

Fortunately, complications associated with fine-needle aspiration are relatively rare. Bleeding, damage to surrounding structures, and fistula creation are all minimized by the small size of the needle. The greatest risk is for bleeding in patients that are coagulopathic for any reason. In these patients, manual compression is typically enough to stop the bleeding. The other major potential complication is to seed tissue planes with infection or neoplastic cells while passing the needle through them to reach the area to be aspirated. This is why it is essential to consider whether a fine-needle aspiration is necessary to guide treatment or whether definitive treatment should be pursued in the absence of fine-needle aspiration.

Clinical Significance

Fine-needle aspiration is a minimally invasive way to get a cell sample from a lesion with the smallest chance of damaging surrounding healthy tissue. In situations of clinical uncertainty, it is a powerful tool to assist in guiding treatment. It is also a way to drain abscesses in cosmetically significant areas such as the breast, albeit with a higher chance of recurrence than traditional incision and drainage. Therefore, fine-needle aspiration is both a diagnostic and therapeutic tool with which healthcare providers of all levels should be familiar.

Enhancing Healthcare Team Outcomes

The most critical step for any fine-needle aspiration is the decision of whether or not it will actually change the management of the patient for whom it is being planned. Everyone on the entire interprofessional healthcare team (clinicians, mid-level practitioners, nurses) should be in agreement that a cytology sample is necessary to determine the appropriate treatment for the patient and that fine-needle aspiration will be sufficient to attain this rather than a more invasive method such as core-needle biopsy or excisional biopsy. When the procedure is being performed, the entire healthcare time should take every precaution necessary to ensure that sterile technique is maintained to minimize the risk of spreading infection.