MIBI-scintigraphy of thyroid nodules – risk of malignancy

Thyroid nodules are a common clinical problem and differential diagnosis between malignant and benign nodules is essential to achieve optimal treatment. Pertechnetate scintigraphy and fine needle aspiration are standard procedures for further diagnosis of ultrasonographically detected thyroid nodules. We report the outcome of a patient using scintigraphy with methoxyisobutylisonitrile (99mTc-MIBI) as an additional diagnostic approach to a cold thyroid nodule. A 64 year old women presented for further diagnosis of an accidentially palpated thyroid nodule. Thyroid function (TSH=1.1 mU/ml) and calcitonin were normal. Ultrasonography showed a normal size of the thyroid (total volume: 15ml) and two nodules, one hyperechoic (volume: 5ml) within the right thyroid and a hypoechoic (volume: 2.3ml) within the isthmus. Pertechnetate scintigraphy (99mTC –PTT, 70 MBq) showed a cold nodulus in the lower part of the right thyroid and a hot nodulus within the isthmus, indicating an unifocal autonomy. Fine needle aspiration of the cold nodulus gave no evidence for malignancy within few monomorphous follicular cells. Additionally performed 99mTc-MIBI -scintigraphy (350 MBq) showed a clear missmatch to the pertechnetate scan: there was a markedly increased uptake within the cold nodulus, suggesting an increased risk for malignancy while MIBI uptake was low in the remaining thyroid, inclusively within the unifocal autonomy. The patient was recommended for surgery to clarify the dignity of the cold and MIBI-positive nodulus. Histology revealed a follicular thyroid carcinoma with multifocal infiltration of the capsule and beginning penetration into the perinodular thyroid tissue. Complete thyroidectomy was performed. Afterwards the patient underwent ablative radiojodtherapy and TSH suppressive thyroxin treatment. Follow up visits for 18 months indicated complete recovery. The use of 99mTc-MIBI-scintigraphy offers an additional tool to assess the risk of malignancy in cold thyroid nodules and to stratify patients for further therapy.