Amyloid Goiter that was Difficult to Distinguish from Malignant Tumor.

A seventy-five-year-old man consulted our clinic, complaining of a rapidly enlarging mass in the left neck arising over the past one month. A hard tumor in the left thyroid lobe and tumor in the left posterior neck were palpated. CT and MRI showed tumor of the left lobe expanding into the thorax and an isolated mass in the left neck. Thyroid function was normal and there were no other general symptom noted.Malignant thyroid tumor and metastatic lymph nodes were preoperatively diagnosed. Therefore, left thyroid lobectomy and neck mass exenteration were performed. Pathological diagnosis with Congo red dye established amyloid goiter without malignant cell. Rectal biopsy postoperatively was also positive for amyloid.This case was thought to be primary amyloid goiter with general extension, and the type of amyloid was AA. The patient's postoperative course has been good without mass recurrence.Pathological diagnosis of thyroid mass has been very varied, but amyloid goiter seems to be underestimated because of its rare incidence. Amyloid goiter tends to rapidly enlarge and becomes hard in some case. Preoperative distinguishing between malignant tumor and amyloid goiter might be clinically very difficult.Many amyloid goiters have a good prognosis without serious symptoms, but goiter may sometimes be fatal due to cardiac failure. Therefore, amyloid goiter should be carefully observed postoperatively.