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Fine needle biopsy is generally considered unreliable in the differential diagnosis of follicular lesions of the thyroid gland. To test this hypothesis, we correlated fine needle biopsy diagnoses with surgical diagnoses in 379 follicular lesions. From nuclear characteristics (especially size) and the architectural pattern of tissue fragments, the following observations were made. Differentiation of goiters (including hyperplastic ones) from neoplastic thyroid disease is quite accurate and no more than 1 to 2% of cancers should be missed. The specific cytologic diagnosis of follicular carcinoma is 75% accurate, and that of follicular variant of papillary carcinoma is over 95% accurate. Of histologically proved follicular carcinomas, almost three-quarters should be diagnosed as such or strongly suspected by fine needle biopsy. The remainder will be identified as cellular follicular adenomas, reaffirming the overlap of cytologic features of benign and malignant neoplastic disease. From cytologic and surgical pathologic data for each fine needle biopsy diagnosis of follicular lesion, a probability of cancer can be stated that is useful in management decisions.

In 24 of 30 patients with lymphoma of the thyroid, the diagnosis was made preoperatively or without surgery; undifferentiated or poorly differentiated carcinoma was suspected in 3 other patients. Thirteen patients were under 60 years of age; 7 were under 40. An increase in the ratio of men to women was seen among younger patients. At presentation, a discrete nodule was found in 19 patients, and multinodular or diffuse goiters in 11. Seventy-six percent of patients with solitary nodules had enlargement of extranodular tissue. Imaging showed "cold" nodules, cold areas in diffuse goiters, or patchy uptake. Nine patients had obstructive complaints; 12 patients had subnormal thyroid function; 24 patients had coexistent Hashimoto's thyroiditis. Lymphoma of the thyroid was suggested by fine-needle biopsy results in 17 of 28 patients (undifferentiated carcinoma was suspected in 2); and by large-needle biopsy results in 21 of 23 (undifferentiated or poorly differentiated carcinoma was suspected in 2). Biopsy of diffuse Hashimoto's goiters is indicated for cold imaging defects, enlarging tender goiter, or goiter enlarging on thyroid hormone. Early diagnosis may improve prognosis for lymphoma of the thyroid, so that surgery or chemotherapy can be avoided.

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.