Vanishing thyroid tumors: a diagnostic dilemma after ultrasonography-guided fine-needle aspiration.

Background: Fine-needle aspiration (FNA) is the most accurate and cost-effective method for evaluating thyroid nodules. However, FNA-induced secondary changes completely replacing thyroid tumors (vanishing tumors) may create a novel problem. In this study, we highlight the diagnostic and management issues associated with the unintended consequences of ultrasonography (US)-guided FNA.

Methods: Fourteen thyroid glands (11 women and 3 men, ages 33-64 years) with vanishing tumors were prospectively identified between 2009 and 2012 upon surgical resection. Cytology and histopathology slides were reviewed, and second opinions were obtained when necessary.

Results: The cytology of the 14 vanishing tumors was suspicious/positive for papillary thyroid carcinoma (PTC) in 5, indeterminate (atypia of unknown significance) in 5, benign in 2, follicular neoplasm in 1, and nondiagnostic in 1 nodule. Upon thyroidectomy, the vanishing tumors ranged in size from 0.4 to 3.5 cm (median 0.7 cm). Microscopically, the nodules showed cystic degeneration, organizing hemorrhage, granulation tissue, fibrosis, and microcalcifications. In seven tumors, a few residual malignant cells (PTC in five) or residual benign follicles (hemorrhagic cyst in two) at the periphery of the vanishing tumors helped with the final diagnosis. The remaining seven tumors were completely replaced by FNA-induced secondary changes, and had the cytology diagnosis of benign in one, follicular neoplasm in one, and suspicious/positive for PTC in five. Of the latter five, two showed additional separate foci of PTC, while three vanishing tumors (0.5, 1.2, and 1.6 cm) had no residual malignant cells and no additional carcinoma leading to a final diagnosis of negative for malignancy.

Conclusions: US-guided FNA may lead to complete obliteration of thyroid nodules, rendering final diagnosis upon thyroidectomy difficult or impossible. In these unusual circumstances, the possibility that the surgical pathology may be nonrepresentative should be considered if the cytologic features on FNA are sufficient by themselves to support a definitive diagnosis of PTC.