Abstract
PurposeTo compare mutation analysis of cytology specimens and 99mTc-MIBI thyroid scintigraphy for differentiating benign from malignant thyroid nodules in patients with a cytological reading of follicular neoplasm.MethodsPatients ≥18 years of age with a solitary hypofunctioning thyroid nodule (≥10 mm), normal thyrotropin and calcitonin levels, and a cytological diagnosis of follicular neoplasm were prospectively enrolled. Mutation analysis and 99mTc-MIBI scintigraphy were performed and patients were subsequently operated on to confirm or exclude a malignant lesion. Mutations for KRAS, HRAS and NRAS and for BRAF and translocations of PAX8/PPARγ, RET/PTC1 and RET/PTC3 were investigated. Static thyroid scintigraphic images were acquired 10 and 60 min after intravenous injection of 200 MBq of 99mTc-MIBI and visually assessed. Additionally, the MIBI washout index was calculated using a semiquantitative method.ResultsIn our series, 26 % of nodules with a follicular pattern on cytology were malignant with a prevalence of follicular carcinomas. 99mTc-MIBI scintigraphy was found to be significantly more accurate (positive likelihood ratio 4.56 for visual assessment and 12.35 for semiquantitative assessment) than mutation analysis (positive likelihood ratio 1.74). A negative 99mTc-MIBI scan reliably excluded malignancy.ConclusionIn patients with a thyroid nodule cytologically diagnosed as a follicular proliferation, semiquantitative analysis of 99mTc-MIBI scintigraphy should be the preferred method for differentiating benign from malignant nodules. It is superior to molecular testing for the presence of differentiated thyroid cancer-associated mutations in fine-needle aspiration cytology sample material.
Highlights
The diagnostic approach to thyroid nodules is usually based on clinical examination, ultrasonography (US) and scintigraphy in suspicious nodules followed by the well-established complementary procedure of fine-needle aspiration cytology (FNAC) [1]
In our series, 26 % of nodules with a follicular pattern on cytology were malignant with a prevalence of follicular carcinomas. 99mTc-MIBI scintigraphy was found to be significantly more accurate than mutation analysis
In patients with a thyroid nodule cytologically diagnosed as a follicular proliferation, semiquantitative analysis of 99mTc-MIBI scintigraphy should be the preferred method for differentiating benign from malignant nodules
Summary
The diagnostic approach to thyroid nodules is usually based on clinical examination, ultrasonography (US) and scintigraphy in suspicious nodules followed by the well-established complementary procedure of fine-needle aspiration cytology (FNAC) [1]. The identification of new diagnostic approaches to provide reliable preoperative criteria for malignancy in patients with indeterminate FNAC is of paramount importance to reduce the number of unnecessary thyroid surgery procedures. Different additional tools have been proposed to increase preoperative accuracy in the assessment of nodules with a follicular pattern on FNAC including US, core-needle biopsy and elastosonography. None of these has proved to be adequate to safely rule out the need for diagnostic surgery in follicular neoplasms [5,6,7]
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