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

– Cyst fluid only (see comment)

COMMENT: The aspirate smears show abundant macrophages, many of which contain intracytoplasmic hemosiderin pigment. There is a background of proteinaceous fluid and blood. No thyroid follicular epithelium is present for evaluation. These 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.

 

– 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.


 

CATEGORY II: BENIGN

0-3% risk of malignancy.

Clinical Management: Clinical follow-up.

  – Benign follicular nodule (Bethesda category 2) (see comment)

COMMENT: The aspirate smears are *** cellular and show scattered clusters of cytologically bland follicular epithelial cells in a background of *** amounts of *** colloid. No features of classic papillary carcinoma are identified. Only occasional microfollicles are seen. These findings are consistent with a benign thyroid nodule. Clinical and ultrasound correlation is suggested.

 

  – Benign follicular nodule, Colloid type (Bethesda category 2) (see comment)

COMMENT: The aspirate smears show abundant amounts of watery colloid. No follicular epithelial cells are identified. There is no evidence of malignancy. In the correct clinical setting, these features are consistent with a benign colloid nodule. Clinical and ultrasound correlation is suggested.

 

– Chronic lymphocytic thyroiditis (Bethesda category 2) (see comment)

COMMENT: The aspirate smears are *** cellular and show a mixed lymphoid population associated with numerous Hürthle cells and fewer bland follicular cells in a background of scant watery colloid. No features of classic papillary thyroid carcinoma are identified. These features are consistent with chronic lymphocytic thyroiditis. Clinical and serologic correlation is recommended.

 

– Granulomatous thyroiditis (Bethesda category 2) (see comment)

COMMENT: The aspirate smears 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/FLUS

5-15% risk of malignancy.

Clinical Management: Repeat FNA.

  – 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 thyroid neoplasm cannot be excluded. Clinical and ultrasound correlation is suggested, with consideration for follow-up with repeat FNA biopsy.

 

  – Follicular lesion of undetermined significance (Bethesda Category 3) (see comment)

COMMENT: The aspirate smears and ThinPrep slide are mildly cellular showing clusters of cells with predominantly microfollicular architecture. Minimal amounts of watery colloid are present in the background. No features of papillary thyroid carcinoma are identified. Overall, the findings support classification as a follicular lesion of undetermined significance (FLUS). Clinical and ultrasound correlation is suggested, with consideration for repeat sampling at an appropriate interval.


 

CATEGORY IV: Follicular Neoplasm

15-30% risk of malignancy.

Clinical Management: Surgical lobectomy.

  – Suspicious for follicular neoplasm (Bethesda category 4) (see comment)

COMMENT: The aspirate smears are *** cellular and show a repetitive microfollicular pattern of cytologically bland follicular epithelial cells occurring singly and in crowded trabecular groups. Definite transgressing blood vessels are not seen. Minimal colloid is present. 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 carcinoma, and non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). Consideration for thyroid lobectomy is suggested for definitive diagnosis, if clinically indicated.

 

  – Suspicious for follicular neoplasm, Hürthle cell type (Bethesda category 4) (see comment)

COMMENT: The aspirate smears and ThinPrep slide are abundantly cellular and show many groups of Hürthle cells with abundant granular cytoplasm and prominent nucleoli. The cells are arranged in microfollicular clusters, crowded trabeculae, and many cells are present singly. A few groups show transgressing blood vessels. There is no significant lymphoid inflammation. The background shows pigmented histiocytes but scant to absent colloid. There are no features of papillary carcinoma identified.  The findings are suspicious for follicular neoplasm of the Hürthle cell type. The differential diagnosis includes adenomatous hyperplasia, a follicular adenoma, and less likely, follicular carcinoma. Consideration for thyroid lobectomy is suggested for definitive diagnosis, if clinically indicated.

 


 

CATEGORY V: SUSPICIOUS

60-75% risk of malignancy.

Clinical Management: Near-total thyroidectomy or surgical lobectomy.

  – Suspicious for papillary thyroid carcinoma (Bethesda category 5) (see comment)

COMMENT: The aspirate smears are *** cellular and show scattered groups of cells with dense squamoid cytoplasm and occasional papillary groups. Definite intranuclear cytoplasmic pseudoinclusions are not well-visualized. These features are suspicious for papillary thyroid carcinoma. Clinical correlation is suggested with consideration for surgical excision for definitive diagnosis.

 


 

CATEGORY VI: MALIGNANT

97-99% risk of malignancy.

Clinical Management: Near-total thyroidectomy.

  – Papillary thyroid carcinoma (Bethesda category 6) (see comment)

COMMENT: The aspirate smears are abundantly to moderately cellular and show sheets and papillary clusters of cells with dense squamoid cytoplasm, irregular nuclear contours, powdery chromatin, and rare nuclear pseudoinclusions. Also present are scattered bizarre multinucleated giant cells and bubble gum colloid. The cytologic features are those of papillary thyroid carcinoma. Clinical and radiographic correlation is recommended.

 

  – Medullary thyroid carcinoma (Bethesda category 6) (see comment)

COMMENT: The aspirate smears are abundantly cellular and show sheets and clusters of epithelioid-to-spindled cells with ovoid nuclei and fine nuclear chromatin. 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.

 

  – 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 anaplastic carcinoma. Clinical and radiographic correlation is recommended.

 

 Last updated: Sep 2, 2019