Vanishing tumors of thyroid: histological variations after fine needle aspiration.

Background: Fine needle aspiration (FNA) can lead to changes that extensively replace cytological confirmed thyroid lesions. These lesions, so called "vanishing tumors" can be diagnostically challenging to pathologists and therapeutically challenging for endocrinologists and surgeons. We performed a retrospective analysis to identify these tumors.

Methods: Data of 656 patients referred for thyroid surgery was reviewed. Patients with suspicious lesions on neck ultrasound (US) underwent FNA. We compared FNA cytological and surgical pathological findings to identify vanishing tumors. FNA-induced changes such as cystic degeneration, hemorrhage, calcification, cholesterol crystals, fibrosis and granulation tissue were identified.

Results: Seventeen patients (2.5%) were identified with vanishing tumors. FNA cytology was indeterminate in seven (41.1%) and benign in ten (58.8%) patients. Surgical pathology in all nodules showed regressive changes partially or entirely replacing the tumor. The mean size of vanishing tumors was 2.4±1.5 cm in greatest dimension. Seven nodules (41.1%) were entirely replaced while remaining ten nodules showed partial replacement of tumors. Three (17.6%) nodules had focal areas of optically clear nuclei suspicious of papillary thyroid carcinoma (PTC); one showed an additional focus of follicular neoplasm (FN) of uncertain malignant potential.

Conclusions: FNA-induced changes can lead to obliteration of nodules rendering pathological diagnosis with no evidence of confirmed lesions. Pathologists and surgeons should be aware of this challenging scenario.