For Thyroid FNA’s the “Bethesda System” has been adopted by the majority of institutions.
It has 6 categories:
CATEGORY I: NONDIAGNOSTIC OR UNSATISFACTORY
1-4% risk of malignancy.
Clinical Management: Repeat FNA with ultrasound-guidance
UCD smartphrase: BT1
– Non-diagnostic (predominantly blood), see comment
COMMENT: The aspirate smears are paucicellular and contain predominantly blood. There is insufficient thyroid follicular epithelium present to evaluate for a thyroid epithelial process. Correlation with clinical and imaging findings is recommended with consideration for repeat sampling, if clinical concern persists.
UCD smartphrase: BT1CYST
– Non-diagnostic (cyst fluid only), see comment
COMMENT: The specimen contains proteinaceous fluid with scattered macrophages and admixed blood. No thyroid follicular cells are present. The findings are diagnostic of sampling of cyst fluid. There is insufficient thyroid follicular epithelium present to evaluate for a thyroid epithelial process. Correlation with clinical and imaging findings is recommended with consideration for repeat sampling of any residual solid component, if clinically indicated.
CATEGORY II: BENIGN
0-3% risk of malignancy.
Clinical Management: Clinical follow-up.
UCD smartphrase: BT2
– Benign follicular nodular disease (Bethesda category 2), see comment
COMMENT: The specimen is *** cellular and shows scattered clusters of cytologically bland follicular epithelial cells with a spectrum of oncocytic change in a background of *** amounts of *** colloid. Only occasional microfollicles are seen. No features of classic papillary carcinoma are identified. These findings are consistent with a benign thyroid nodule.
UCD smartphrase: BT2CN (CN: Colloid Nodule)
– Benign follicular nodular disease (Bethesda category 2), see comment
COMMENT: The specimen is mildly cellular and shows abundant colloid with scattered clusters of cytologically bland follicular epithelial cells. No features of classic papillary carcinoma are identified. These findings are consistent with a benign thyroid nodule and are suggestive of a colloid nodule in the appropriate clinical/radiographic setting.
UCD smartphrase: BT2CLT (CLT: Chronic Lymphocytic Thyroiditis)
– Chronic lymphocytic thyroiditis (Bethesda category 2), see comment
COMMENT: The smears are cellular and show a mixed lymphoid population associated with numerous/predominant oncocytic cells with mild endocrine atypia and fewer bland follicular cells in a background of scant watery colloid. No features of classic papillary carcinoma are identified. Only occasional microfollicles are seen. These findings are consistent with chronic lymphocytic thyroiditis. Clinical and serologic correlation is suggested.
UCD smartphrase: BT2GT (GT: Granulomatous thyroiditis)
–Granulomatous thyroiditis (Bethesda category 2), see comment
COMMENT: The smears are cellular and show numerous epithelioid histiocytes in a background of multinucleated giant cells and moderate amounts of watery and dense colloid. Scattered clusters of cytologically bland follicular epithelium are seen. No repetitive microfollicular pattern is seen and no classic features of papillary carcinoma are identified. The overall findings are consistent with granulomatous thyroiditis, and the differential diagnosis includes subacute (De Quervain’s) thyroiditis, palpation thyroiditis, as well as an infectious process. Clinical and radiographic correlation is suggested.
CATEGORY III: AUS
5-15% risk of malignancy.
Clinical Management: Repeat FNA.
If there are mild PTC-like nuclear changes:
UCD smartphrase: BT3
– Atypia of Undetermined Significance (Bethesda Category 3), see comment
COMMENT: The aspirate smears are *** cellular and show *** [crowding, dense squamoid cytoplasm, enlarged nuclei, grooves etc.]. No well-formed intranuclear pseudoinclusions are identified. The background is notable for *** amounts of *** colloid. The morphologic findings are best characterized as atypia of undetermined significance (AUS). While the findings could represent a benign thyroid nodule, the possibility of a thyroid neoplasm cannot be excluded. Clinical and ultrasound correlation is suggested, with consideration for follow-up with repeat sampling as clinically indicated.
If there are microfollicles, but not “enough” to call a follicular neoplasm:
– Atypia of Undetermined Significance (Bethesda Category 3), see comment
COMMENT: The aspirate smears are mildly cellular and show bland follicular epithelium. Notably, the majority of these groups show abnormal microfollicular architecture, raising the possibility of a follicular neoplasm. However, given the only mild cellularity and probable background watery colloid, we think that this sample is best categorized as “Atypia of Undetermined Significance.” Clinical and radiologic correlation is recommended.
If there are Psamommatous calcifications, but no cytologic atypia:
– Atypia of Undetermined Significance (Bethesda Category 3), see comment
COMMENT: The specimen is mildly cellular and shows scattered clusters of cytologically bland follicular epithelial cells with a spectrum of oncocytic change in a background of mild amounts of watery colloid. A single Psammomatous calcification is present. A single adjacent cell is also present with marked nucleomegaly, coarse chromatin, and prominent nucleoli. No other features of classic papillary carcinoma are identified.
The morphologic findings are best characterized as atypia of undetermined significance (AUS). Psammomatous calcifications in isolation are associated with both benign and malignant thyroid aspirates, including papillary thyroid carcinoma. Clinical and ultrasound correlation is suggested, with consideration for molecular testing or follow-up with repeat sampling as clinically indicated.
CATEGORY IV: Follicular Neoplasm
15-30% risk of malignancy.
Clinical Management: Surgical lobectomy.
UCD smartphrase: BT4FN (FN: Follicular Neoplasm)
–Follicular neoplasm (Bethesda category 4), see comment
COMMENT: Cellular smears show follicular epithelium arranged in predominantly microfollicules with mild nucleomegaly and focal overlapping. Definite transgressing blood vessels are not seen. Minimal colloid is present. Nuclear features of papillary thyroid carcinoma are not seen. Overall, these findings are suspicious for a follicular neoplasm and the differential diagnosis includes follicular adenoma, follicular nodular disease and follicular carcinoma. Clinical and radiologic correlation is recommended.
(+/- NIFTP QuickText, below)
Mild nuclear atypia including occasional grooves and irregular nuclear membranes are noted. No pseudoinclusions are identified. These findings also raise the possibility of a non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). Clinical and radiologic correlation is recommended.
UCD smartphrase: BT4ON (ON: Oncocytic Neoplasm)
– Follicular neoplasm, Oncocytic/Hürthle cell type (Bethesda category 4), see comment
COMMENT: Cellular smears show predominantly oncocytes (Hürthle cells) in syncytial sheets, crowded clusters, and microfollicles with mild nucleomegaly and prominent nucleoli. There is no significant lymphoid inflammation. The background shows scant to absent colloid. There are no features of papillary carcinoma identified. Overall, these findings are suggestive of an oncocytic (Hurthle cell) neoplasm, and the differential diagnosis includes follicular nodular disease with extensive oncocytic metaplasia, oncocytic adenoma, oncocytic carcinoma as well as parathyroid adenoma. However, an oncocytic variant of papillary thyroid carcinoma and medullary carcinoma cannot be entirely excluded. Clinical and radiologic correlation is recommended.
CATEGORY V: SUSPICIOUS
60-75% risk of malignancy.
Clinical Management: Near-total thyroidectomy or surgical lobectomy.
UCD smartphrase: BT5
– Suspicious for papillary thyroid carcinoma (Bethesda category 5), see comment
COMMENT: Cellular aspirate smears show sheets and small clusters of cells displaying mild nucleomegaly, pale chromatin, occasional nuclear grooves, and mild nuclear membrane irregularities. No well-defined nuclear pseudoinclusions, papillae or psammomatous calcifications are present. The cytologic features are suspicious for papillary thyroid carcinoma, however, a non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) cannot be completely excluded. Clinical and radiologic correlation is recommended..
CATEGORY VI: MALIGNANT
97-99% risk of malignancy.
Clinical Management: Near-total thyroidectomy.
UCD smartphrase: BT6PTC (PTC: Papillary thyroid carcinoma)
– Papillary thyroid carcinoma (Bethesda category 6), see comment
COMMENT: Cellular aspirate smears show papillary clusters and sheets of cells displaying PTC-like features (nucleomegaly, pale coarse chromatin, nuclear grooves, mild nuclear membrane irregularities and scattered intranuclear inclusions). The cytologic features are consistent with papillary thyroid carcinoma (PTC). No foci of necrosis or conspicuous mitotic activity is noted. Clinical and radiologic correlation is recommended.
UCD smartphrase: BT6MTC (MTC: Medullary thyroid carcinoma)
– Medullary thyroid carcinoma (Bethesda category 6), see comment
COMMENT: Cellular aspirate smears show discohesive as well as syncytial sheets of monomorphic large cells with spindled to plasmacytoid morphology, ovoid nuclei, coarse granular chromatin, abundant granular cytoplasm, occasional nuclear inclusions and binucleated cells. Some fragments of dense amorphous stroma are noted suggestive of amyloid. The cytologic features are compatible with medullary thyroid carcinoma. No foci of necrosis or conspicuous mitotic activity is noted. Clinical (esp. serum calcitonin levels) and radiologic correlation is recommended.
(The cell blocks show similar findings. Immunohistochemical stains are positive for calcitonin, synaptophysin, and chromogranin. The morphologic and immunohistochemical findings support a diagnosis of medullary thyroid carcinoma)
UCD smartphrase: BT6PDC (PDC: Poorly-differentiated carcinoma)
– Malignant neoplasm (Bethesda category 6), see comment
COMMENT:The aspirate is focally cellular and shows discohesive and loosely cohesive malignant epithelioid cells with high pleomorphism, enlarged nuclei with irregular nuclear contours, prominent nucleoli and moderate to ample amount of cytoplasm. Bizarre nuclei and tumor giant cells are also noted. Occasional mitotic figures and infiltrative neutrophils are present. The cytologic features are consistent with a malignant neoplasm and differential diagnosis includes anaplastic thyroid carcinoma, poorly differentiated thyroid carcinoma and medullary thyroid carcinoma with high degree of pleomorphism. A metastatic tumor to the thyroid gland cannot be excluded. Clinical and radiologic correlation is recommended.
UCD smartphrase: BT6ATC (ATC: Anaplastic thyroid carcinoma)
– Anaplastic (undifferentiated) carcinoma (Bethesda category 6) (see comment)
– High-grade carcinoma, consistent with Anaplastic (undifferentiated) carcinoma (Bethesda category 6) (see comment)
COMMENT: The aspirate smears are abundantly cellular and show a discohesive population of malignant cells with large, pleomorphic nuclei in a background of necrosis and inflammation. Several osteoclast-like giant cells are identified. No classic features of papillary thyroid carcinoma are identified. Overall, these findings are consistent with a high-grade carcinoma and, given the clinical setting, likely represent anaplastic thyroid carcinoma. Clinical and radiographic correlation is recommended.
Last updated: 1/31/24