Evaluation of thyroid nodules – combined use of 99mTc‐methylisobutylnitrile scintigraphy and aspiration cytology to assess risk of malignancy and stratify patients for surgical or nonsurgical therapy – a retrospective cohort study

Abstract

Thyroid nodules are a common clinical problem, and differentiation between benign and malignant nodules is essential. The aim of this study was to evaluate an approach for cold thyroid nodules including (99m)Tc-methylisobutylnitrile (MIBI) scintigraphy to assess risk of malignancy and stratify patients for therapy. Retrospective cohort study; 391 patients with at least one cold thyroid nodule were consecutively admitted (between 1 January 2004 and 31 December 2006) and recommended for surgical or nonsurgical therapy. Thyroid ultrasonography, (99m)Tc-pertechnetate scintigraphy, laboratory tests, fine needle aspiration cytology (FNAC) and MIBI scintigraphy. 57·3% (224/391) had one cold nodule, 17·9% (70/391) had several cold nodules, and 24·8% (97/391) had both cold and hot nodules. MIBI scintigraphy was classified into 'positive' (16·1%, 63/391), 'weakly positive' (19·2%, 75/391) or 'negative' (64·7%, 253/391). FNAC was classified into benign (87·9%, 247/281), nondiagnostic (6·8%, 19/281) or suspicious/malignant (5·3%, 15/281). 127 patients received surgery, revealing malignancy in 13·3% (17/127), predominantly papillary (64·7%, 11/17) and follicular carcinoma (23·5%, 4/17). MIBI scintigraphy was 'positive' (64·7%, 11/17) or 'weakly positive' (23·5%, 4/17) in most patients with malignant findings. FNAC was unavailable in 23·5% (4/17) with malignancy, positive in 38·5% (5/13) and negative in 61·5% (8/13). Among patients undergoing surgery, sensitivity, specificity, negative and positive predictive values for MIBI scintigraphy were 88·2%, 35·5%, 95·1% and 17·4%, for FNAC 38·5%, 90·6%, 90·6% and 38·5%, respectively, and for the combination (MIBI scan + FNAC) 92·3%, 30·6%, 96·3% and 16·9%. Benign MIBI-positive nodules were predominantly follicular adenomas (68%, 33/48). Evaluation of cold thyroid nodules by MIBI scintigraphy aids therapeutic decisions: MIBI-negative findings support nonsurgical management in about two-thirds of patients, while MIBI-positive findings have an increased risk of malignancy, supporting surgical therapy. However, the positive predictive value was low, which requires further research.