From the Guidelines
A fine-needle aspiration (FNA) biopsy of the thyroid gland should demonstrate a specific cytopathological diagnosis, with results categorized into six diagnostic categories: benign, malignant, atypia of undetermined significance (AUS), follicular neoplasm, suspicious for malignancy, or nondiagnostic/unsatisfactory 1.
Diagnostic Categories
- Category I: nondiagnostic or unsatisfactory biopsy
- Category II: benign (e.g., nodular goiter, colloid goiter, hyperplastic/adenomatoid nodule, Hashimoto’s thyroiditis)
- Category III: atypia of undetermined significance (AUS) or follicular lesion of undetermined significance (FLUS)
- Category IV: follicular neoplasm or suspicious for follicular neoplasm (includes Hürthle cell neoplasm)
- Category V: suspicious for malignancy
- Category VI: malignancy (includes papillary, medullary, anaplastic, or lymphoma) The biopsy sample should be evaluated for the presence of cellular features such as papillary formations, nuclear grooves, and intranuclear pseudoinclusions, which are characteristic of papillary thyroid carcinoma 1. Molecular diagnostic testing, such as BRAF V600E mutation analysis, may also be useful in evaluating FNA samples that are indeterminate to assist in management decisions 1.
Key Features
- Papillary formations: characteristic of papillary thyroid carcinoma
- Nuclear grooves: characteristic of papillary thyroid carcinoma
- Intranuclear pseudoinclusions: characteristic of papillary thyroid carcinoma
- BRAF V600E mutation: occurs in approximately 45% of papillary carcinomas 1
From the Research
Fine-Needle Aspiration Biopsy of the Thyroid Gland
A fine-needle aspiration (FNA) biopsy of the thyroid gland should show specific cytopathological features to diagnose thyroid lesions accurately. The following are some key features to look for:
- Papillary architecture
- Multinucleated giant cells
- Nuclear pseudo-inclusions
- Nuclear grooves
- Micronucleoli
- Powdery chromatin
- Psammoma bodies 2
- Cohesive flat sheets
- Distinct cell borders
- Nuclear enlargement
- Dense granular cytoplasm
- Small distinct nucleoli
- Fine chromatin
- Elongate to spindled cytomorphology 3
Diagnostic Criteria
The presence of certain cytopathological features can help diagnose papillary thyroid carcinoma. For example:
- Nuclear grooves and micronucleoli are commonly seen in papillary thyroid carcinoma 2, 4
- Psammoma bodies are highly specific for papillary thyroid carcinoma 2
- A combination of nuclear grooves, micronucleoli, pseudo-inclusions, powdery chromatin, and multinucleated giant cells can be 100% specific in detecting papillary thyroid carcinoma 2
Atypical Cells
Atypical cells can be seen in both benign and malignant thyroid lesions. The presence of atypical cells with distinct cell borders, elongated shape, eosinophilic cytoplasm, and distinct nucleoli can be indicative of benign cyst-lining cells 3. However, the presence of nuclear crowding, intranuclear pseudoinclusions, and papillary architecture can be indicative of malignant cells 3.
Second-Opinion Cytopathology Review
A second-opinion cytopathology review of thyroid FNA biopsies can reduce the need for diagnostic thyroidectomy, especially in patients with indeterminate FNA biopsies 5. This review can help improve the accuracy of FNA biopsy results and avoid unnecessary surgery.
False-Negative Rate
The false-negative rate of thyroid FNA biopsies can vary depending on the institution and the specific criteria used. However, studies have shown that the false-negative rate can be around 5-6% 6. Interpretation errors are more likely to occur in follicular patterned neoplasms, while sampling errors are more common in non-follicular variants of papillary thyroid carcinoma.