The diagnosis of malignant follicular neoplasms of the thyroid by needle biopsy.

To test the value of needle biopsy for a diagnosis of follicular thyroid malignancy, we compared needle biopsy and surgical diagnoses for 1005 patients. There were 67 follicular carcinomas, 34 Hurthle cell carcinomas, and 39 follicular variants of papillary carcinoma. Malignancy was diagnosed or suspected by biopsy for 114 of the cancers (82%), considered "possible" for 24 (17%), and misdiagnosed as "benign" in 2. Sensitivity of fine-needle biopsy (FNB) for the diagnosis of 39 cancers approximated that of large-needle biopsy (LNB) for 101 cancers 2 cm or larger. Diagnostic specificity for cancer varied with the degree of cytologic or histologic abnormality. Specificity of FNB was comparable to LNB on nodules large enough for both procedures. Specificity of FNB on nodules too small for LNB was substantially less. The sensitivity of needle biopsy allows selection of many follicular nodules for observation. Knowledge of the probability of cancer for each cytologic or histologic diagnosis is useful in determination of the need for thyroid surgery.