Thyroid fine-needle aspiration biopsy (FNAB) is a simple, cost-effective and minimally traumatic technique for the diagnosis of thyroid nodules. We report on two cases of acute thyroid swelling after FNAB. In both cases, within two hours after completion of the procedure, the entire thyroid gland enlarged rapidly. Ultrasound showed diffuse swelling of the entire thyroid gland with a heterogeneous appearance. There were no signs of bleeding or airway obstruction. The next morning a repeat US showed that the thyroid had returned to its normal size.
It has been demonstrated that nerve fibers storing neuropeptides such as vasoactive intestinal peptide, substance P, cholecystokinin, neuropeptide Y, peptide histidine isoleucine, galanin, and calcitonin gene-­related peptide (CGRP) exist in the thyroid.
The clinical and ultrasound data support the hypothesis of capillary leakage as the underlying mechanism, possibly evoked by neuropeptide release.