Fine Needle Aspiration (FNA)


FNA is a common procedure done in the office with local anesthesia. It is the best way to diagnose thyroid cancer. Its accuracy approaches 95%. A small amount of local anesthetic is injected into the skin and the underlying tissues. This is the most uncomfortable part of the procedure. A small needle is inserted into the nodule usually under ultrasound guidance. There is a mild aching sensation when the biopsy is taken. The actual procedure takes only a few seconds. Patients tolerate it well. Most patients comment that the worse part is the anxiety about the procedure not the discomfort. Some bruising may occur but significant issues with bleeding are rare. Any mild residual discomfort is easily handled with ice and tylenol. Narcotic pain medication is not required. Be sure to tell us if you are on blood thinners. Aspirin, plavix or aggrenox are okay but coumadin should be stopped a few days before the biopsy.

The pathologist commonly assigns the results of a needle biopsy to one of 6 categories:

  • Category 1: non-diagnostic
  • Category 2: benign
  • Category 3: indeterminate ( less likely to be malignant: maybe a 25-30% risk)
  • Category 4: indeterminate (somewhat more likely to be malignant; maybe a 40-50% risk)
  • Category 5: suspicious for malignancy ( 85-90% risk)
  • Category 6: diagnostic of malignancy ( >99% risk)

Once we do an FNA, we have the patient come back in a few days to discuss the findings. There are four possible outcomes:

  1. The biopsy is positive. It is concerning for, or diagnostic of cancer ( category 6)
  2. The biopsy is negative. It shows benign changes ( category 2).
  3. The biopsy is indeterminate. (categories 3 and 4)
  4. The biopsy is non-diagnostic. The pathologist cannot draw a conclusion ( category 1)

If the FNA is diagnostic of cancer it will almost always be papillary cancer, the most common type of thyroid cancer.  If a definitive diagnosis for papillary cancer is seen on FNA, then we can proceed with definitive surgery. Total thyroidectomy with central lymph-node removal is our usual approach.

If the FNA is definitively benign then observation may be considered. Follow-up ultrasound is require (typically in 6 months)  to ensure that the nodule is stable as there is a small single digit percentage risk of false negative results with any FNA

An “indeterminate” result (commonly reported as “follicular neoplasm”) is a more complicated problem and is more completely discussed on the next page. We need to discuss follicular neoplasms in more detail.  A common “indeterminate” result on FNA is “follicular neoplasm”. “Follicular” refers to the appearance of the specimen under the microscope. “Neoplasm” is a medical term for a growth or tumor. It does not indicate if it is cancer or not. If a follicular neoplasm is benign it is called a follicular adenoma. If a follicular neoplasm is cancer it is called a follicular carcinoma.

The nature of a follicular neoplasm can only be determined by detailed examination of the tumor by a pathologist after the tumor has been completely removed. If invasion of tumor cells is seen into the lining of the tumor or into blood vessels in the tumor, then the pathologist calls it follicular cancer. This is impossible to see on a needle biopsy and very difficult to see on the preliminary pathological exam at the time of surgery (frozen section). When we get a diagnosis of follicular or hurthle cell neoplasm on FNA  a complicated decision tree presents itself.  A variety of issues may keep the pathologist from drawing a conclusion about the nature of a nodule. Sampling errors, processing errors or interpretive errors may occur. Sometimes conclusions are impossible. Each case is individualized. Sometimes repeat biopsy is appropriate. Sometimes surgery is recommended. Sometimes, observation and repeat ultrasound in a few months is the best approach. Which of these approaches is the most appropriate depends on the individual circumstances of the patient and the potential causes of the indeterminate biopsy. Each case is individualized. A second pathologic opinion or thyroid lobectomy for diagnosis may be recommended. If surgery is recommended  we usually have to wait for the final report from the pathologist. This may take several days. If a benign adenoma is found then nothing else is required. If cancer is found the we have to go back to surgery to remove the remaining thyroid lobe. This is called a “completion thyroidectomy”

If the FNA is negative then, generally, observation is appropriate. Surgery may still be considered if the lesion is very large (greater than 4 cm) or causing local symptoms or if the patient is very anxious about the nodule.

A subsequent page shows a slide show of a FNA procedure.