Vanishing tumors of thyroid: histological variations after fine needle aspiration

Fine needle aspiration (FNA) cytology is considered the gold standard in the diagnosis of thyroid nodules that may require surgical excision. The advent of FNA has led to a decreased number of unnecessary surgeries performed for benign thyroid tumors; however, malignant nodules can be missed in a minority of cases (1,2). The reported sensitivity of thyroid FNA results is 65–99% while its specificity is 72–100% (3-5). A standard protocol followed after detection of a thyroid nodule on palpation is to perform a thyroid ultrasound (US). According to the revised guidelines of the American Thyroid Association (ATA), thyroid US is being increasingly used for nodules >1 cm in size. Nodules presenting with US features suspicious of malignancy, such as presence of micro-calcification, hypo-echogenicity, “taller-than-wide” shape and increased vascularity, are subsequently examined by FNA biopsy to detect the presence and type of cancer cells (6). However, 15–20% of the nodules are deemed indeterminate on cytological results (7). The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) uses three categories that fall in the “grey zone” between benign and malignant cytology: follicular lesion of undetermined significance/atypia of undetermined significance (FLUS/AUS), suspicion for follicular neoplasm (FN)/Hürthle cell neoplasm, and suspicious for malignancy, the sensitivity of which is variable according to different investigators (7-11). The definite diagnosis of these nodules is provided by histological examination following surgical excision of the tumor