Diffuse sclerosing variant of papillary thyroid carcinoma. Clinicopathologic study of 15 cases.

We report 15 cases of a distinctive variant of thyroid papillary carcinoma designated as "diffuse sclerosing papillary carcinoma" (DSPC). This lesion is characterized by the following morphologic findings: (a) diffuse involvement of one or both lobes, (b) numerous micropapillary formations located within cleftlike spaces consistent with lymph vessels, (c) extensive squamous metaplasia, (d) large number of psammoma bodies, (e) marked lymphocytic infiltration, (f) prominent fibrosis. Of all these features, we believe the widespread intrathyroid lymphatic permeation to be the most important, in the sense of conditioning the other morphologic findings and the behavior of the tumor. When compared with conventional papillary carcinoma, the DSPC variant exhibits the following characteristics: (a) similar predilection for women, (b) younger age at the time of presentation, (c) greater incidence of cervical lymph node involvement, (d) greater incidence of lung metastases, (e) smaller probability of disease-free survival on follow-up. The practical importance of the recognition of this variant of papillary carcinoma lies in its ability to clinically simulate thyroiditis and the more aggressive therapeutic approach that might be needed to eradicate it.