Occlusive phlebitis, a diagnostic feature in Riedel's thyroiditis.

Five cases of Riedel's invasive fibrous thyroiditis are presented. Clinically and histopathologically all cases fulfilled the criteria for this lesion. In both small and large veins there were inflammatory changes and obliteration of the lumen, followed by sclerosis. These changes were found in each operative specimen, and seemed to be a diagnostic feature of invasive fibrous thyroiditis. We consider this change to be an occlusive phlebitis, and have noted that it occurs in association with multifocal fibrosclerosis. Three stages can be recognised: infiltrative, occlusive and sclerotic. In other thyroid lesions such as Hashimoto's thyroiditis, granulomatous thyroiditis of the Quervain type and adenomatous goitre these peculiar changes in the veins were not found.