Thyroid FNA: Clinical Information, Specimen Procurement Technique Handling and Preparation
Zubair W. Baloch, MD, PhD & Martha Bishop Pitman, MD
Clinical Information
It is not uncommon for the cytopathologist to interpret thyroid FNA with minimal or no clinical information. Cytology FNA requisition form just stating "thyroid nodule" in the clinical history is not acceptable. Cytologic interpretation of thyroid FNA should only be performed when adequate clinical history is provided. The clinical information should include:
- Age and sex of the patient
- Location and size of the nodule
- History of prior surgery, radiation to head and neck area and prior FNA
- Thyroid function tests and thyroid radionuclide scan results (most helpful in case of multiple nodules).
- Radiologic/Sonographic appearance of the nodule (cystic vs. solid vs. mixed, and presence or absence of calcification) and surrounding thyroid. Though this data may seem excessive, we believe the above-mentioned information is much needed for correct interpretation of thyroid FNA. For example, hyper-functioning nodules can give rise to cellular aspirates and be mistaken for lesion/neoplasm and in some cases also may mimic features suspicious for papillary carcinoma. Specimen Procurement Technique
A thyroid nodule can be aspirated manually or under radiologic guidance. Manual aspiration usually requires experience on the part of aspirator. The needle size is important in FNA of thyroid nodules. Smaller gauge needle are more likely to cause excessive bleeding leading to non-diagnostic and poorly fixed specimens. A 25-gauge needle attached to a 10-ml syringe with or without aspiration is recommended. It is advisable that no more than 4 passes should be performed, since too many passes into a nodule leads to much bleeding, dilution of specimen by blood and may adversely affect the adequacy of specimen. At least 2 passes in different quadrants of the thyroid nodule should be performed to achieve a detailed cytologic picture since the majority of thyroid lesions are heterogeneous in morphology. Ultrasound guidance can significantly improve the sensitivity and specificity of thyroid FNA and decrease the non-diagnostic rate as compared to manual thyroid FNA. This is especially true in thyroid lesions, which are: - Difficult to palpate due to smaller size.
- Arising in the posterior aspect of the thyroid
- Nodules associated with diffuse pathologic processes such as lymphocytic thyroiditis, and Graves' disease. - In addition, ultrasound guided thyroid FNA is helpful in the diagnosis of palpable thyroid nodules, which are deemed non-diagnostic on manual FNA due to extensive cystic change or fibrosis. In such cases, ultrasound-guidance can clearly target the solid portion of the nodule to acquire diagnostic material. Specimen Preparation and On-site Evaluation
The on-site evaluation of thyroid specimens with rapid cytology stains leads to adequate specimens and dramatically reduces non-diagnostic rates; however, this may not be possible in all clinical settings. The clinical utility of the on-site assessment of thyroid FNA is similar to the interpretation of frozen sections in surgical pathology. A number of questions can be answered by on-site evaluation, which include: adequacy of specimen, classification of lesion, and specimen triage for additional studies (flow cytometry, serum calcitonin measurements to rule out medullary carcinoma and genetic studies). If the smears are made on-site, they should be:
- Made on clean glass slides.
- Thicker than regular hematology smears, this can be achieved by applying gentle pressure during smearing to keep the cellular integrity. - The number of smears should be kept low, 2-3 smears/pass. - They can be air dried for Romanowsky stain or fixed in 95% alcohol or spray fixed for Papanicolaou stain. The Romanowsky staining method is one of the best available methods available in cytology for immediate evaluation of thyroid FNA specimens. This stain can:
- Highlight the background watery colloid and cell architecture (papillary, monolayer sheets, and macro- and micro-follicles).
- Distinguish between cell types (follicular, Hürthle, lymphocytes and macrophages). Papanicolaou stain is vital to the diagnosis of thyroid lesion. It effectively highlights:
- The nuclear details and alterations (grooves and inclusions), which are crucial for the diagnosis of papillary thyroid carcinoma. - It also is helpful in the diagnosis of Hürthle cell and C-cell lesions. In cases where on-site evaluation is not possible, alcohol fixed smears are preferable since the nuclear details can be readily identified by Papanicolaou stain. If possible the material should be equally divided between smears and other preparations, such as cytospins, Thin Prep, Millipore Filter, cell block; however, this depends upon the preferences and facilities of individual practices.
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