Thyroid Cytopathology Reporting by the Bethesda System: A Two-Year Prospective Study in an Academic Institution

Table 1

The Bethesda System for reporting thyroid cytopathology: recommended diagnostic categories, implied risk of malignancy, and recommended clinical management.

Diagnostic category	Risk of malignancy (%)	Usual management^a
(I) Nondiagnostic or unsatisfactory (ND/UNS)		Repeat FNA with ultrasound guidance
Cyst fluid only
Virtually acellular specimen
Other (obscuring blood, clotting artifact, etc.)
(II) Benign	0–3	Clinical follow-up
Consistent with a benign follicular nodule (includes adenomatoid nodule,colloid nodule etc.)
Consistent with lymphocytic (Hashimoto) thyroiditis in the proper clinical context
Consistent with granulomatous (subacute) thyroiditis
Other
(III) Atypia of undetermined significance or follicular lesion of undetermined significance (AUS/FLUS)	5–15^b	Repeat FNA
(IV) Follicular neoplasm or suspicious for follicular neoplasm  (FN/SFN)	15–30	Surgical lobectomy
-specify if Hürthle cell (oncocytic) type
(V)  Suspicious for malignancy (SFM)	60–75	Near-total thyroidectomy or surgical lobectomy^c
Suspicious for papillary carcinoma
Suspicious for medullary carcinoma
Suspicious for metastatic carcinoma
Suspicious for lymphoma
Other
(VI) Malignant	97–99	Near-total thyroidectomy^c
Papillary thyroid carcinoma
Poorly differentiated carcinoma
Medullary thyroid carcinoma
Undifferentiated (anaplastic) carcinoma
Squamous cell carcinoma
Carcinoma with mixed features (specify)
Metastatic carcinoma
Non-Hodgkin lymphoma
Other

Actual management may depend on other factors (e.g., clinical and sonographic) besides the FNA interpretation.
^bEstimate extrapolated from histopathologic data from patients with “repeated atypicals” [7, 26].
^cIn the case of “suspicious for metastatic tumor” or a “malignant” interpretation indicating metastatic tumor rather than a primary thyroid malignancy, surgery may not be indicated.