The rational use of fine needle aspiration biopsy (FNAB) in diagnosing thyroid nodules

Fine needle aspiration biopsy (FNAB) plays a crucial role in the diagnosis of thyroid nodules and enables the number of surgical operations to be reduced. Theoretically, FNAB should be carried out on all nodules, though currently only those displaying certain characteristics are biopsied. Indeed, to perform FNAB on all nodules may be regarded as an excess of zeal. Therefore, it seems advisable that the endocrinologist should be able to confirm on the spot the necessity and utility of FNAB.

We evaluated on a sample of 263 consecutive requests (209 female, 57 male; age 56.7+/-13.7 years) for FNAB in 2004: 1) the appropriateness of the investigation, 2) expected efficacy, 3) practical efficacy, 4) efficiency. FNAB was performed under echo-guidance in accordance with the standard technique. In 50%, 36%, 6%, 3%, 2% and 1% of cases, the echographic diagnosis was of MNG, UNG, pseudo-nodular lesion in ATD, lymph-node, neck cyst, suspected parathyroid lesion and tumefaction of the salivary glands, respectively. A pre-FNAB clinical risk score was assigned to each case on the basis of clinical and echographic data, with a maximum possible score of 11. The results of FNAB were subdivided into 5 categories according to the criteria of the BTA (Thy1-Thy5). After FNAB, a decisional category was assigned, ranging from ''observation'' to ''surgery''; this was subsequently (7-18 months) compared with the management strategy adopted by the attending physician. Information was gathered by means of telephone enquiry.

1) Appropriateness: on the basis of clinical and echographic findings, FNAB was not judged appropriate in 24% of cases because of either the lack of confirmation of a significant target (34%) or a low pre-FNAB risk score (range 0-2) (66%). The decisional category was ''observation'' in 87% of cases and ''further investigation'' in 13%. 2) Expected efficacy: FNAB was performed in 76% of cases. The biopsies (3%) performed on swollen lymph-nodes and extra-thyroid neck tumefactions, in which biochemical evaluation was positive, proved to be diagnostic but not classifiable according to the BTA. In 82% of the remaining cases, the result was Thy2 (observation) or Thy 4-5 (surgery). Thy3 results (surgery) were rare (1%). Thy1 results (16%) were yielded by the aspiration of colloid cysts (29%), solid lesions (10%) characterised by means of PTH-FNAB and Tg-FNAB, nodules (9%) no longer detectable on repetition of FNAB, nodules (16%) in which FNAB was already a repetition of a non-diagnostic investigation (2003), and nodules (9%) in which the presence of normal thyrocytes, ''hot'' scintigraphic image and prior decision of the surgeon advised against repeating FNAB. Of the patients with Thy1 results, 26% refused to repeat FNAB. In all, 95% of FNAB supported by biochemical evaluation yielded results that usefully contributed to patient management. The correlation between pre-FNAB clinical risk and cytological score according to the BTA proved significant (P<0.001). No difference in diameter was recorded between nodules with adequate cytology (23.3+/-0.9 mm) and those with inadequate cytology (25.2+/-1.6 mm). 3) Practical efficacy: 75% of patients were reached by telephone. In most cases, observation was the most frequent clinical choice, after echography and/or FNAB. The decisional category assigned after FNAB correlated significantly (P<0.001) with the approach adopted by the attending physician. d) Efficiency: following FNAB, 11 patients were assigned to surgery. DTC was detected in 100% of these cases (1 follicular carcinoma, 1 insular carcinoma, 9 papillary carcinoma). The success of FNAB (9/11) in detecting lesions that proved malignant on histological examination (11/11) was significant (P<0.05). Of the 2 Thy 3 cases, 1 was follicular carcinoma and 1 was follicular adenoma with adjacent papillary carcinoma. The incidence of thyroid carcinomas in the population studied was 5.5%.

1) Together with clinical-biochemical evaluation, echo-guided FNAB re-mains the first-line diagnostic test in the management of thyroid nodules; 2) a pre-FNAB clinical risk score is useful in limiting the number of probably inappropriate investigations; 3) efficacy, in terms of cytology results that are useful for patient management after FNAB (and after biochemical evaluation, when indicated) is high, enabling patients to be stratified in classes with different subsequent pathways; 4) in the vast majority of cases, FNAB influences subsequent clinical decisions; 5) false negatives cannot be excluded, while false positives are practically nil; 6) further indications may be yielded by studies on larger populations, and new prospects may emerge from the application of other techniques associated to FNAB.