Correlation of cytologic and histologic findings in fibrosing thyroiditis. A case report.

Background: Fibrous thyroiditis is the rarest form of thyroiditis. Consequently, needle aspiration biopsy experience is limited. Aspirates generally yield paucicellular smears with, at the most, only occasional, small fragments of connective tissue.

Case: A 35-year-old man presented with a firm right thyroid mass. Aspiration yielded cellular smears with round and irregularly shaped, cellular aggregates. Coarse cytoplasmic granules and intranuclear inclusions were also noted. The lesion was surgically excised, and pathologic examination was consistent with fibrous thyroiditis.

Conclusion: As confirmed by histopathologic examination, the aspirated atypical cellular aggregates represented thyroid follicular units that were distorted by entrapment within fibrous tissue. Fibrosing thyroiditis may yield an atypical smear pattern.