Extensive sterile abscess in an invasive fibrous thyroiditis (Riedel's thyroiditis) caused by an occlusive vasculitis.

Riedel's thyroiditis is a rare disease determined by an invasive fibrosclerotic transformation of the thyroid gland. It may be one manifestation of multifocal fibrosis with still unknown etiology. Because it mimics carcinoma, a biopsy must be performed to get the correct diagnosis. The condition is self-limiting when confined to the neck. Prognosis depends on the extent of extracervical fibrosclerosis. We present a patient with a huge cervical and mediastinal, unilateral thyroid mass expanding to the aortic curve, which led to tracheal deviation and compression with symptoms of stridor and dyspnea. These symptoms continued under a course of high-dose steroids; thus an operation was necessary to relieve the airway obstruction and limit inflammation. Intraoperative and pathological findings showed an inflammatory infiltration of the adjacent neck muscles and a sterile abscess caused by an occlusive vasculitis. Therefore, hemithyroidectomy had to be performed instead of a local limited resection.