Relative sensitivity of thyroid fine-needle aspiration by tumor type and size

Background: Fine-needle aspiration (FNA) of papillary thyroid carcinoma (PTC) has high sensitivity. Previous studies demonstrated correlation between FNA sensitivity and PTC size, and lower sensitivity for follicular variant of PTC (FVPTC). Data are lacking for other types of thyroid carcinomas.

Methods: 996 resected thyroid carcinomas at two institutions (6- and 10-year periods) were correlated with FNA diagnoses and clinical and radiologic data to determine sensitivity for each malignancy type.

Results: There were 867 PTCs (371 FVPTC), 101 follicular carcinomas (FCs) (31 oncocytic), 16 medullary carcinomas, and 12 poorly differentiated carcinomas (PDCAR). Mean size of classical PTC (CPTC; 1.9 cm) was smaller than FVPTC (2.2 cm), FC (3.0 cm), oncocytic FC (3.0 cm), and PDCAR (2.8 cm) (P<0.003 each), but not medullary carcinoma (1.7 cm) (P=0.45). Sensitivity was higher for CPTC (88%), compared to FVPTC (78%; P<0.0001) and FC (71%; P=0.0006) and was lower for FC than PDCAR (100%; P<0.04). For tumors ≤1.0 cm, FNA sensitivity for CPTC was higher than for FVPTC (P=0.02). For tumors 1.1-2.9 cm, sensitivity for CPTC was better than FVPTC (P=0.0001) and FC (P=0.0008). Between size groups, only CPTC showed a significant change with decreased sensitivity for tumors ≥3.0 cm (P<0.003).

Conclusion: FNA is more sensitive for CPTC, PDCAR, and medullary carcinoma. For CPTC, FNA sensitivity is highest for tumors 1.1-2.9 cm. FNA sensitivity is higher for CPTC than FVPTC for nodules <3.0 cm. FNA sensitivity is lower for FC than CPTC and PDCAR.