Vanishing Thyroid Nodules: A Rare Diagnostic Dilemma Induced by Ultrasound-Guided Fine-Needle Aspiration

Fine-needle aspiration (FNA) is the most accurate and cost-effective method for evaluating thyroid nodules. Ultrasound-guided FNA is recommended for nodules with suspicious sonographic characteristics. The newly developed Bethesda System for Reporting Thyroid Cytopathology provides diagnostic categories with implied risk of malignancy and management recommendations. Rarely, secondary reactive changes following FNA may completely replace the nodule, rendering its diagnosis difficult or impossible on final surgical pathology of the thyroid resection (“vanishing nodule”). We present our experience with these nodules and discuss diagnostic and management issues. Cases were prospectively identified during routine cytology-surgical pathology correlation reviews between 2009-2010. The cytology and surgical pathology slides from the vanishing nodules were sent separately to 2 experts in endocrine cytopathology and surgical pathology, respectively, each blinded to the diagnosis rendered by the other and to the original diagnosis. A final determination about the nature of the nodule was made after considering all opinions. Vanishing nodules ranging in size from 0.4 to 3.5 cm (median, 1 cm) were identified in 4 women and 2 men aged 36 to 56 years. In resected surgical specimens, the 6 nodules showed cystic change, hemorrhage, granulation tissue, and fibrosis and/or microcalcifications. A benign diagnosis was made based on a few residual colloid filled follicles in 2 nodules (“nearly vanished” nodules) with benign and inadequate cytology in 1 nodule each. No residual diagnostic follicles were present in the remaining 4 vanished nodules, the cytologic diagnoses for which were papillary carcinoma (PC) in 2, suspicious for PC in 1, and benign in 1. FNA may rarely cause complete obliteration of thyroid nodules, making final diagnosis on surgical pathology difficult or impossible. In these rare events, the cytology reviewed in consultation with experts may provide the final diagnosis.