Multimodality Molecular Imaging (FDG-PET/CT, US Elastography, and DWI-MRI) as Complimentary Adjunct for Enhancing Diagnostic Confidence in Reported Intermediate Risk Category Thyroid Nodules on Bethesda Thyroid Cytopathology Reporting System

Abstract

The potential complimentary role of various molecular imaging modalities [fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT), ultrasound (US)-elastography, and diffusion weighted imaging-magnetic resonance imaging (DWI-MRI)] in characterizing thyroid nodules, which have been designated as "intermediate risk category" on the Bethesda thyroid cytopathology reporting system (BTCRS), is illustrated in this communication. The clinical cases described (category III thyroid nodules on BTCRS) show the imaging features and the final diagnostic impressions rendered by the interpreting physicians with the modalities that have been independently compared in a tabular format at the end; of particular note is the high negative predictive value of these (specifically FDG-PET/CT), which could aid in enhancing the diagnostic confidence in the reported "intermediate risk category" thyroid nodules, a "gray zone" from the patient management viewpoint.

Keywords: Diffusion weighted imaging-magnetic resonance imaging (DWI-MRI); fine-needle aspiration cytology (FNAC); fluorodeoxyglucose-positron emission tomography/computed tomography (18F-FDG-PET/CT); ultrasound (US)-elastography.

Figure 1

(a) Grey scale ultrasonography demonstrating mixed echogenecity predominantly hyperechoic lesion (6.1 × 3.9 cm) with central macrocalcification (b) Split-screen B-mode ultrasound image (left) and US elastogram (right) showing a focal stiff nodule (star) with predominantly maintained elasticity. The Rago and Asteria Strain elastographic scores of the lesion were 3 and 2 (c and d). Plain axial MRI images showing heterogeneous signal intensity on T2W and predominantly hypointensity on T1W images respectively. Also noted was central darkly hypointense area on both T2W and T1W images representing calcification (arrow) (e and f). Diffusion colored maps of EADC and ADC value obtained from ADC map with b factor 0 and 500. The ADC map shows low values of in the area of stiffness on elastogram (star) corresponds to restricted diffusion with a measured ADC value of 0.34 × 10-3 mm2/s. (g) FDG-PET/CT demonstrating very low grade FDG uptake in the nodule

Figure 2

(a) Grey scale transverse ultrasound showing a heterogeneous predominantly iso to hypoechoic lesion (3.7 × 1.9 cm) that was cold on 99mTcO4 scintigraphy. (b) Split-screen B-mode ultrasound image (left) and US elastogram (right) showing a predominant stiff nodule (star). The Rago and Asteria Strain elastographic scores of the lesion were 3 and 3 respectively. (c and d) Plain MRI showing a predominantly iso-to hypointense on both T2W images and T1W images respectively. (e and f). Diffusion colored maps of EADC and ADC value obtained from ADC map with b factor 0 and 500. The ADC map of the left side nodule (star) showed diffusion pattern similar to the normal parenchyma the right lobe of thyroid with a measured ADC value of 1.82 × 10-3 mm2/s which represented area of stiffness on elastogram. (g) FDG-PET/CT demonstrating a predominantly to be FDG non-avid nodule in a background of diffuse uptake indicating associated thyroiditis like picture in the rest of the thyroid gland