The thyroid is an endocrine gland just below Adam's apple located in the front portion of the neck, in front of the trachea, or 'windpipe'. It has two lobes (rounded divisions or sections), joined by a thin bridge of tissue called the 'isthmus' of the thyroid. This gland is responsible for producing thyroid hormone. .Thyroid nodules represent a common problem in endocrinology. Their prevalence is higher in women (5 per cent) than in men (1 per cent). Thyroid nodules are also more frequently seen in:• elderly people• those with a history of irradiation to the head and neck• those who eat a diet containing a high amount of goitrogensCancer can be present in 3-10 per cent of nodules, depending on age, gender, radiation exposure history, family history and other factors. The methods currently used for assessing thyroid nodules include fine-needle aspiration cytology (FNAC), thyroid scan and ultrasound. Test explainedThyroid Fine Needle Aspiration Cytology (FNAC) of the thyroid gland is now a well-established, first-line diagnostic test for the evaluation of diffuse thyroid lesions as well as thyroid nodules. It has a sensitivity rate of about 95 per cent, i.e. false-negative results represent up to 5 per cent of cases. FNAC has led to a decrease in the number of thyroid surgeries and an increase in cancer detected during thyroid surgery. Ultrasound-guided FNAC should be used for:•\thypoechoic nodules (a mass on the thyroid that appears darker on the ultrasound than the surrounding tissue)•\twhen aspiration cytology fails to yield adequate cellular material for testing•\twhen the size of the nodule is smallPerforming the testA thyroid FNAC is an outpatient procedure for most people. It takes up to half an hour, followed by a short period afterwards when you will be watched until you have recovered and can leave the hospital. You are generally allowed to resume normal work. You can eat and drink normally before and after the procedure. During the test, the lesion is needled with a fine needle quickly and gently at different angles and points of entry. From the aspirate in the hub of the needle slides are prepared. Thyroid FNAC is typically performed using 22 to 25 gauge needles and 10 or 20 ml syringes that may, or may not be attached to a "pistol-grip" device.Thyroid FNAC is a very safe procedure and is considered a very low risk for most Anatomy of the thyroid and parathyroid glands people because the needle that is used is so small. It is common to have some pain, swelling and even a little bruise where the needle was inserted into your neck. Local haemorrhage may lead to haemotoma formation.Test interpretationMost pathologists report thyroid FNAC according to the Bethesda system. The Bethesda system uses six categories for thyroid cytology reporting, and each category is supplemented by a list of criteria. Category I Non-diagnostic Category II BenignCategory Ill Atypia of undetermined significance (AUS)Category IV Follicular neoplasm/suspicious for follicular neoplasm (SFN)Category V Suspicious for malignancy MalignantCategory VI MalignantLimitationsScanty samples, vascularity of thyroid swelling, variation in sampling technique and skill of the performing expert as well as the experience of pathologist interpreting the aspirate do pose a problem in definitive diagnosis.Drawbacks• The inability of FNAC to distinguish a follicular adenoma from a follicular carcinoma.• False-negative may generally occur in cystic lesions, lymphoma in the background of Hashimoto thyroiditis.