Sarcoma of the thyroid region mimicking Riedel's thyroiditis

Because sarcomas of the anterior lower neck region occur so infrequently, t hey are not usually considered in the differential diagnosis of Riedel's th yroiditis. Riedel's thyroiditis itself may be confused on clinical grounds alone with malignant neoplasms because of its invasive features. Sarcomatoi d carcinoma is the main entity to be discarded in this regard. This is acco mplished through histological examination by the finding of carcinomatous a reas and/or reactivity with epithelial markers. These features also set apa rt sarcomatoid carcinoma from true sarcomas. This report concerns a patient with a sarcoma of the anterior lower neck region which was initially suspe cted to be Riedel's thyroiditis or sarcomatoid carcinoma on clinical and ra diological grounds. A peroperative biopsy was interpreted by two independen t pathologists as consistent with Riedel's thyroiditis. The subsequent clin ical course and postmortem examination demonstrated a high grade sarcoma wi th metastasis to both lungs and the pleura, and invasion of adjacent neck s tructures. Nevertheless, some areas of the postmortem material showed a mic roscopic pattern similar to mediastinal fibrosis, raising the possibility o f the malignant transformation of a fibrosclerotic lesion.