Papillary Carcinoma Obscured by Complication with Subacute Thyroiditis: Sequential Ultrasonographic and Histopathological Findings in Five Cases

Background: Subacute thyroiditis (SAT) has been rarely reported to coexist with thyroid carcinomas. The objective of the study was to assess sequential ultrasonographic and histopathological findings of SAT in the context of complicating thyroid carcinomas. Methods: Of 1152 patients with SAT who visited our thyroid clinic at Kuma Hospital from 1996 through 2006, 5 cases complicated by papillary carcinoma underwent surgical resection 3-16 months after SAT onset. Ultrasonographic examinations and thyroid function tests were performed in all patients at onset of SAT and just before surgery. Sequential histopathological features of regenerated thyroid and carcinoma involvement were evaluated. Results: Heterogenous areas with microcalcifications in the thyroid or lymphadenopathy in three patients were clues for the nodular involvement with papillary carcinoma on the initial ultrasonographic examination. In contrast, diffuse hypoechoic change in the thyroid in two patients made it impossible to differentiate nodular involvement from inflammatory lesion. Histopathological examination of surgical specimens showed granulomatous and fibrotic changes. These were present about 3 months from SAT onset, and residual fibrosis remained several additional months, in the condition of no inflammatory hypoechoic lesions. In the areas of papillary carcinoma overlapping with transient inflammatory involvement, some lymphocytes and fibrotic changes were present in the stroma of papillary foci, but no granulomatous formation was present in any sections. Continuity with fibrosis around regenerated follicular cells was absent. The degree of lymphoid infiltrate and fibrotic change in the papillary carcinoma was not dependent on periods between SAT onset and the resection. Conclusions: SAT may produce ultrasound changes that obscure the coexistence of papillary carcinoma, but affects no lymphoid infiltrate and fibrotic changes involved in carcinoma throughout the clinical course. We recommend that patients with SAT have ultrasonography after they recover. Further workup, including cytological examination of hypoechoic regions, should be performed if they are present as measuring 1 cm or larger.