Thyroid gland biopsyMedical editor Arne Heilo MD
Oslo University Hospital
An ultrasound-guided cytological biopsy, also called fine needle aspiration cytology (FNAC) is, in many cases, the most precise diagnostic method for work-up of a tumor in the thyroid gland. WIth today's ultrasound equipment, the point of the needle can be placed within an area of about 2-3 mm.
For ultrasound guided FNAC of the thyroid gland, it is important that a cytologist or screener is present to immediately evaluate the quality of the material. This facilitates collection of a high number of representative samples. It also allows opportunities for collecting material for supplementary examinations.
In certain cases, it will be necessary to take a supplementary tissue sample for a histological biopsy to make a more definite diagnosis.
- Palpable tumor
- Solitary or dominant tumor ≥ 1 cm detected by ultrasound examination
- Diffuse and enlarged, rapid-growing tumor in the thyroid gland
For a tumor that is not palpable < 1 cm, FNA is indicated if:
- there is familial accumulation of the disease
- the patient has previously been irradiated to the neck
- there are detected suspect lymph nodes in the neck
- ultrasound finding gives suspicion of malignancy
- Diagnose a tumor in the thyroid gland
For examination and puncture of the thyroid gland, a linear ultrasound (US) probe with high contrast is ordinarily used (10–15 MHz). Patients with large struma often require a US sound probe with better tissue penetration (lower ultrasound frequency) for a satisfactory result, however, this reduces the contrast detail significantly.
For the cytology biopsy, a 27 G needle is used, or sometimes a 25 G needle is used.
For the histological biopsy, a biopsy gun is used for automatic biopsy taking with a biopsy needle size 16-18 G.
- Local anesthesia is ordinarily not necessary for cytological biopsies, but should always be used for histological biopsies because of the needle thickness.
- The patient lies with their neck dorsally flexed by a pillow under the neck.
- The patient must hold their head still and not swallow during the puncture.
- For the cytology biopsy, the sample is taken without aspirating. The capillary action of the needle alone collects the best material for cytology testing.
- The needle is located in the tumor and moved in an out in the same plane.
Normally, there are two to four punctures made in the area to be tested. The exception is when it is necessary to aspirate and/or use a thicker needle (23 G) to, for example, drain a cyst or when there is fibrosis in the thyroid gland.
It is recommended that a diagnostic sample contain at least six groups of follicle epithelial cells in each of at least two punctures.
If there are cysts, as much fluid should be evacuated as possible. A cell sample from the remaining lesion should be taken if necessary (without aspiration).
All cyst fluid should be examined (make at least 2-6 smears of fresh fluid).
The material should be immediately smeared on a slide to avoid coagulation. The slide should be air-dried, fixed, and stained.
For the histology biopsy, the skin area is washed and the procedure is carried out aseptically. After placing the local anesthesia using US guidance, a small incision is made to insert the larger needle. When the point of the needle is in the correct position, the shooting mechanism is triggered and the sample is taken automatically. Because local anesthesia is given, the procedure usually does not cause any discomfort.
- Complications from the procedure are rare.
- Mild irritation at the puncture point may occur.
- Cytology and histology biopsies can, in rare cases, cause bleeding in the thyroid gland or in surrounding tissue.
- The result of the test is usually available after 2 days.