Fine Needle Aspiration of a Thyroid Nodule (FNA)
Investigation of thyroid nodule(s). 80% of all thyroid nodules are "cold" on technetium or iodine scan, and 85 to 90% of these cold nodules are benign. Thus the prime aim of FNA is to exclude malignancy (note however that 9% of nodules that are apparently functioning on isotope scanning turn out to be malignant, i.e. scanning alone is a poor test to exclude malignancy and may be becoming obsolete as a first line investigation of nodules).
Rarely: local bleeding. Avoid by applying local pressure
- Contact cytology department who will come almost immediately and bring their prepared slides.
- Lie patient in supine position with neck flexed backwards.
- Insert 25 gauge needle into nodule and aspirate (usually more than one pass). Local anaesthesia is usually necessary. The needle should just be passed in and out. Don't draw back as this results in a bloody tap.
- Negative" or benign: obvious epithelial cells ± colloid
- Hashimoto's (hypercellular)
- Suspicious of neoplasm: papillary etc.
- Diagnostic of neoplasm
- Non-diagnostic: insufficient cells to make a diagnosis
1) and 2) do nothing, ?follow up if necessary. No indication for T4 treatment to "suppress" nodule unless function tests show raised TSH (i.e. "subclinical hypothyroidism").
3) Repeat FNA, radioisotope scan: if focal abnormality refer to Mr Lynn
4) Refer Mr Lynn
5) Consider repeat FNA. Do isotope scan ± ultrasound.
SENSITIVITY AND SPECIFICITY
Depends on the centre. At the Hammersmith we have as yet little experience and cannot say. Experienced centres report 98% sensitivity and over 99% specificity. The major limiting factor may be the quality of the sample.
Gabib H et al., Endo. Metab. Clin. N. Am. 17, 511-26 (1988).