Type of test Microscopic examination of tissue
Normal findings
Benign
Test explanation and related physiology
FNAB is used to obtain tissue to rule out cancer in a “cold” (does not light up on a thyroid scan) thyroid nodule or cyst of a patient whose thyroid function is normal. In FNAB, samples of thyroid tissue are obtained by placing a very thin needle into the thyroid nodule and obtaining small pieces of thyroid tissue that are then examined microscopically. The Bethesda System for Reporting Thyroid Cytopathology is used to provide the results of the biopsy. Results are indicated as the following: non diagnostic (insufficient tissue for evaluation), benign, atypia of undetermined significance, suspicious for a follicular neoplasm, suspicious for malignancy, or malignant. The implied risk of malignancy for each diagnostic category is shown in the following table.
FNAB samples can be challenging to interpret and produce indeterminate results in 15% to 30% of cases. Approximately 70% to 80% of the time, the nodules prove to be benign for cancer by surgical pathology.
Contraindications
• Patients with coagulation disorders because of the risk of excessive bleeding
• Patients with hyperthyroidism, because the needle insertion may instigate thyroid storm and toxic nodular goiters are not malignant.
Potential complications
• Hemorrhage from the highly vascular thyroid tissue
• Cyst formation in the thyroid gland
• Infection when an open biopsy is performed
Procedure and patient care
Before
* Explain the procedure to the patient.
• Ensure that the physician obtains informed consent.
* Inform the patient that no abstinence from food or drink is required.
* Tell the patient that no sedative is required.
• Note that the needle stick may be done at the bedside.
• If ultrasound guidance is to be used, note that the needle stick is performed in the radiology or ultrasonography department.
During
• Note the following procedural steps:
1. The patient is placed in a supine position with a sandbag or pillow under the shoulder to hyperextend the neck.
2. Under sterile conditions, the skin overlying the thyroid is infiltrated with a local anesthetic (lidocaine).
3. If the nodule can be felt, a biopsy can be performed in the doctor’s office. When the nodule is not palpable, ultra sound is used to help guide the biopsy.
4. The patient holds her or his breath while the needle is rocked gently to obtain as much tissue as possible.
5. The needle is then withdrawn and tissue is placed on a glass slide.
After
• Apply pressure over the thyroid area to minimize bleeding.
• Note that a physician performs this procedure in approximately 10 minutes.
Abnormal findings
- Malignancy
