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A fine needle aspiration biopsy using ultrasound is a diagnostic test commonly done on a lump in the thyroid that sometimes cannot be felt by touch. The ultrasound scan uses sound waves to create a picture that can be seen on a monitor, which is like a small television screen. The picture helps the doctors pinpoint the area where the biopsy is to be done. The endocrinologists at Houston Thyroid and Endocrine review the pictures and make a report. The biopsy is removal of tissue or fluid samples from a lump to examine under a microscope. A pathologist is another physician who reviews the biopsy samples and gives a report to the endocrinologist. The results of this procedure can provide information that the doctor needs to determine what treatment is indicated.
There are four basic results from a thyroid FNA:
1) Benign
2) Malignant
4) Non-diagnostic insufficient sample
Each of these results may determine a different course of action which your endocrinologist will review with you. The below diagram shows diagnostic categories for the FNA biopsy. The gold standard for determining malignancy potential of a nodule is thyroid surgical pathology. If all patients with these categories were sent for surgery the approximate likelihood of malignancy is shown.
Legend:
* The usual management depends on multiple other factors besides the FNA result such as sonographic findings.
** These are estimates based on resections performed after 'repeated atypicals.'
*** In the cases of suspicious for metastatic tumor or malignant, interpretation indicating metastatic disease from another location may not require thyroid surgery.
Low Risk Lesions
Lymphocytic thyroiditis: This is also known as Hashimoto thyroiditis.
Granulomatous thyroiditis: Also known as subacute thyroiditis
Colloid nodule: Low to moderate cellularity but also has abundant colloid. Risk of malignancy is <1%
Non-diagnostic specimen: There is not enough sample to meet cellular adequacy as defined as 6 well visualized cell groups, each group with at least 10 cells, preferably on a single slide. Risk of malignancy is probably low if the needle was within the nodule but no exact risk can be quoted.
Indeterminate Lesions
Gene analysis can now used on these types of nodules and changes the likelihood of the cancer risk. Treatment plan needs to be individualized depending on patient risk factors, ultrasound characteristics, and other factors.
Indeterminate-follicular-lesion, favor-benign: Risk of malignancy is 2 to 10 %. Some institutions would classify these as ACUS.
Atypical-cells-of-undetermined-significance (ACUS): Minor features or few cells demonstrating something that if were in greater abundance would be suspicious or malignant. Risk of malignancy is 7 to 20%
Follicular lesion: This is a very cellular specimen without nuclear or cellular atypia that would be suspicious for follicular neoplasm. Risk of malignancy is around 7-10%.
Hurthle cell lesion: A very cellular specimen without nuclear atypia that would be suspicious for Hurthle cell neoplasm. Risk of malignancy is 7%-45%. Some would not differentiate this from probable malignancy / Hurthle cell neoplasm.
Probable Malignancy
Patients with these highly suspicious nodules are generally recommended to have an operation to complete the evaluation.
Follicular neoplasm: Cellular specimen with a predominant microfollicular pattern with minimal to no colloid or an aspirate which demonstrates unusual findings such as a solid or trabecular pattern, nuclear enlargement and/or irregularity (not Hurthle cell change), mitotic figures or necrosis. Risk of malignancy is 20%
Hurthle cell neoplasm: Cellular specimen exclusively composed of Hurthle cells with little colloid. Risk of malignancy is 15-45%. If the aspirate has low cellularity but is composed of pure Hurthle cells, can also be an indeterminate follicular lesion.
Suspicious for malignancy: Specimen obtained is just short of a malignant call; at this point the pathologist generally feels the nodule should usually come out with frozen section confirmation prior to total thyroidectomy if clinically indicated. Risk of malignancy is 60-75%.
Malignancy: Risk of cancer is almost certain. 97-99%
Ultrasound Procedure
You will be taken to the examination room, where you will lie on an examination table with a pillow under your neck. A gel is applied to your skin in the area where the lump is located. This gel provides contact between your skin and the transducer of the ultrasound. The transducer sends and receives sound waves that will create pictures on the monitor. During this part of the procedure, you may feel the transducer rubbing across your skin.
Biopsy Procedure
During the biopsy your doctor will will inject a local anesthetic to numb the underlying skin and tissues. This numbing medication can cause a brief burning sensation. Then a very thin needle is inserted through the skin and into the lump. The needle is thinner than needles used for drawing blood; you may feel a pressure-like sensation which is normal. The doctor will remove a small sample of tissue or fluid from the site. More than one biopsy sample may be taken. Some patients worry that passing a needle through a cancer site might cause it to spread. Studies have shown that this procedure will not affect the spread of cancer. During the biopsy, you will be asked to wait 5-10 minutes while the tissue samples are examined to try to ensure there is enough sample for the pathologist to interpret.
After the Procedure
You may have minor pain and bruising in the area where the biopsy was taken. This does not require medicine other than over the counter acetaminophen. If you have any unusual pain or swelling, call your doctor. Your doctor will receive the final test results usually within 15 business days. Very rare complications can include bleeding, skin infections, inserting the needle into the esophagous or wind pipe, and allergic reactions to lidocaine (no epinephrine is used). Expect a call from the office to discuss the results.
Results
The report of a thyroid fine needle biopsy will usually indicate one of the following treatment follow up options:
A) The nodule is benign (noncancerous).
This result is obtained in up to 80% of biopsies. The risk of overlooking a cancer when the biopsy is benign is generally less than 3 in 100 tests or 3%. This is even lower when the biopsy is reviewed by an experienced pathologist at a major medical center. Generally, benign thyroid nodules do not need to be removed unless they are causing symptoms like choking or difficulty swallowing or there are very suspicious features seen on ultrasound examination. Follow up ultrasound exams are important. Occasionally, another biopsy may be required in the future, especially if the nodule grows over time.
B) The nodule is malignant (cancerous) or suspicious for malignancy .
Malignant result is obtained in about 5-10% of biopsies and is most often due to papillary cancer, which is the most common type of thyroid cancer and indicates a 95% certainty of cancer on the surgery. A suspicious biopsy has a 50-75% risk of cancer in the nodule. These diagnoses require multiple steps, starting with surgical removal of the thyroid after consultation with your endocrinologist and surgeon.
C) The nodule is indeterminate.
This is actually a group of several diagnoses that may occur in up to 7-20% of biopsy cases. An Indeterminate finding means that even though an adequate number of cells was removed during the fine needle biopsy, examination with a microscope cannot reliably classify the result as benign or cancer.
The biopsy may be indeterminate because the nodule is described as a Follicular Lesion. These nodules are cancerous 20- 30% of the time. However, the diagnosis can only be made by surgery. Since the odds that the nodule is not a cancer are much better here (70-80%), only the side of the thyroid with the nodule is usually removed. If a cancer is found, the remaining thyroid gland usually must be removed as well. If the surgery confirms that no cancer is present, no additional surgery to complete the thyroidectomy is necessary.
The biopsy may also be indeterminate because the cells from the nodule have features that cannot be placed in one of the other diagnostic categories. This diagnosis is called atypia, or a follicular lesion of undetermined significance. Diagnoses in this category will contain cancer rarely, so repeat evaluation with FNA or surgical biopsy to remove half of the thyroid containing the nodule is usually recommended.
Genetic testing on Indeterminate nodules may increase, decrease, or keep the risk of malignancy at the residual 20-30% rate. Ask your doctor if these tests might be helpful for evaluating your thyroid nodule.
D) The biopsy may also be nondiagnostic or inadequate. This result is obtained in less than 5% of cases when an ultrasound is used to guide the FNA. This result indicates that not enough cells were obtained to make a diagnosis but is a common result if the nodule is a cyst. These nodules may require reevaluation with second fine needle biopsy, or may need to be removed surgically depending on the clinical judgment of your doctor.
References:
Edmund S. Cibas, Syed Z. Ali. Thyroid. November 2009, 19(11): 1159-1165. doi:10.1089/thy.2009.0274.
MDACC cytopathology internal
Lewis CM et al. 2009 Thyroid 19(7) 717-722.
Cooper DS et al. 2009 Thyroid 19(11) 1167-214
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