Fine needle aspiration cytology
	This technique has emerged as a valuable tool in the diagnosis and management of nodular thyroid disease. In contrast to the techniques already described, which provide at best an indirect evaluation of the nature of the disease, fine needle aspiration provides a means of obtaining thyroid tissue for direct cytological examination without the need for surgery. The technique requires practice in order to reduce sampling error and to obtain satisfactory smears with high frequency and, most importantly, the skills of an expert cytopathologist. The procedure can be performed in an outpatient department, is well tolerated by the patient, and can be repeated. The cytopathologist can report that an adequate smear contains normal cells only, cells from benign non-tumorous conditions such as lymphocytic thyroiditis, or suspicious (indeterminate) or frankly malignant cells. The report that is indeterminate or suspicious of malignant change should be regarded as an indication to proceed to surgical exploration - in the same way as a report of unequivocal malignancy indicating papillary, follicular or medullary carcinoma. Prolonged evaluation of the technique, especially in Sweden where it has been applied for more than 25 years, has demonstrated that in the hands of a skilled cytopathologist excellent diagnostic accuracy (of up to 90%) can be achieved. A false positive report of malignant change is extremely rare but the rate of false negatives (i.e. tissue thought to be benign at cytology but found to show malignant change at surgery) is 5-l0% in most series (34). This in part is due to difficulty in distinguishing benign adenomas from malignant follicular neoplasms (34); surgical excision of all such lesions is therefore required. An analysis from Cusick et al. (35) suggested, however, that the technique may be less reliable than is widely accepted. Analysis of their original data revealed an overall accuracy of 92% (36) but audit of a further prospective evaluation showed an accuracy of only 69% (35). Conflicting data in reported studies may relate to the clinical nature of the swellings included (multinodular, isolated or dominant), frequency of operation, and methods used to calculate accuracy. Since 1984 we have routinely carried out fine needle aspiration in all euthyroid patients presenting with thyroid enlargement. We have examined outcome in 629 consecutive patients followed for a minimum of 12 months after first aspirate. Patients were classified as having benign or suspicious/malignant cytological features after their first aspirate. The former group (83% of the total) was managed conservatively, apart from those requiring surgery because of thyroid size or patient preference, and the latter group (17%) proceeded to histological examination. In total, 76% of patients were observed and 24% underwent partial or subtotal thyroidectomy. Of 529 patients with benign cytological findings, clinical follow up of all and surgery in a minority suggested that "true negative" cytology was present in 520. There were 9 "false negative" reports relating to sampling error - 3 cases of papillary carcinoma, 2 follicular carcinomas and 4 follicular adenomas. Seventeen "malignant" cytological reports correctly identified thyroid malignancy and there was one false positive report; 82 "suspicious" reports prompting surgery identified 39 "true positive" cases of thyroid neoplasia (including cancers and follicular adenomas); 43 of this group had benign colloid goitre. These results indicate a diagnostic accuracy of the cytological findings of up to 92%. A diagnosis of thyroid cyst was made in 14% of our series of patients presenting with solitary nodules on clinical examination. These patients were investigated only by fine needle aspiration but had they proceeded to radionuclide scanning, such lesions would have appeared "cold". Approximately 50% of such patients were cured by simple aspiration of cyst fluid, thus avoiding thyroid surgery. Thus in addition to its diagnostic role, aspiration of thyroid nodules may be of therapeutic importance.