Bethesda System for Thyroid FNA - Summary from NCI meeting, 2009
Nondiagnostic or Unsatisfactory (< 10%)
Cyst fluid only. Virtually acellular. < 6 groups of 10 follicular cells (exceptions: abundant colloid, atypia or specific dx as Hashimoto. Other: CFO/cyst fluid only (macrophages only), obscuring blood, thick smear, air drying, clothing artifact and others. Risk of malignancy for ND/US is 1-4%. For CFO is 4%. Repeat FNA if clinically or sonographic worrisome. For persistent nodules consider excision.
Non malignany cells identified (Benign)
Most are benign follicular nodules (multinodular goiter or adenomas), showing adequate # of follicular cells (macrofollicles) and colloid. Repeat FNA if clinically or sonography worrisome. Other: Hashimoto, subacute thyroiditis, etc.
Atypical cells of undetermined significance (AUS)/ follicular Lesion of Undetermined Significance (< 7%)
Numerous microfollicles and scant colloid, not enough for dx of Follicular Neo or suspicious for Follicular Neo. Abundant hurhtle cells with scant colloid, cellular sample with exclusive Hurthle (may be related with goiter or hashimoto). Focal features suggestive of papillary carcinoma may happen in hashimoto, radiation, goiter due to involution, hemorrhage, cyst lining cells. Also in this category atypia due to air dyring or clotting artifact. Atypical lymphoid infiltrate (recommend flow).The estimated risk of malignancy for AUS is 5-15%. the risk may be higher if clinically or sonographic worrisome: repeat or remit to surgery if clinically or sonographic worrisome (20% have Ca after surgery). As a general rule, remember that AUS confers an intermediate risk of malignancy and recommendation to repeat FNA in 3 to 6 months is the initial approach. If repeated FNA is benign follow up. If AUS again, remit to surgery. Most misdiagnosed cases with AUS are papillary carcinomas.
Follicular Neoplasm or Suspicious for Follicular Neoplasm/Hurthle Cells neoplasms
High cellularity, microfollicular or trabecular pattern, frequent crowding and overlapping, scant or absent colloid. FNA is not diagnostic for Follicular Ca (screening test or triage for lobectomy). 35% are goiter and less than 30% malignant. If intact spheres or macrofollicles with only few microfollicles = probably benign. If only Hurthle cells dx may be nodular goiter, hashimoto, hurthle cell adenomas or Ca.
Suspicious for Malignancy
1 or 2 features of PTC present, only focal change or sample sparsely cellular (75% are papillary Ca after lobectomy). For questionable Medullary Ca and lymphoma order IHC and flow.
Positive for malignant cells (malignant) Conclusive for malignancy.