This is the most important test and should be performed on almost all thyroid lumps. Fine needle aspiration involves removing a few cells from within a lump for microscopic examination using a small needle. The test is done in the clinic and provides a rapid aid to diagnosis. Examples of cells taken in this way are shown below.
Following assessment a thyroid lump can be categorised into five groups called the Thy Classification:
Thy 1. Non-diagnostic
- no clear answer on biopsy. Biopsy should be repeated. If persistently in this category serious consideration should be given to surgery.
Thy 2. Benign
- the lump can be safely left alone. National guidelines in the UK are for a second biopsy 2-3 months later as a a final check. Some patients will opt to have benign lumps removed because they are causing problems.
Thy 3. Indeterminate
- this category is usually due to a type of growth of the thyroid gland. Lumps in this category are usually benign but approximately 15% are malignant.
Thy 4. Suspicious
- cells are suspicious of malignancy. Most of these lumps will be require a second biopsy and ultimately surgery.
Thy 5. Malignant
- cells and features seen consistent with thyroid malignancy. This is usually papillary thyroid cancer but other rarer types can be identified e.g., medullary or anaplastic.