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CASE REPORT
Year : 2016  |  Volume : 15  |  Issue : 2  |  Page : 130-133

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


1 Radiation Medicine Centre, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
2 Department of Radiology, Tata Memorial Hospital Annexe, Mumbai, Maharashtra, India

Date of Web Publication3-Mar-2016

Correspondence Address:
Sandip Basu
Radiation Medicine Centre (BARC), Tata Memorial Hospital Annexe, Jerbai Wadia Road, Parel, Mumbai - 400 012, Maharashtra
India
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DOI: 10.4103/1450-1147.176883

PMID: 27134564

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   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 ( 18 F-FDG-PET/CT), ultrasound (US)-elastography


How to cite this article:
Basu S, Mahajan A, Arya S. 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. World J Nucl Med 2016;15:130-3

How to cite this URL:
Basu S, Mahajan A, Arya S. 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. World J Nucl Med [serial online] 2016 [cited 2020 Aug 4];15:130-3. Available from: http://www.wjnm.org/text.asp?2016/15/2/130/176883


   Introduction Top


The category III of the Bethesda thyroid cytopathology reporting system (BTCRS) is designated as "Atypia of Undetermined Significance or Follicular Lesion of Undetermined Significance." The risk of malignancy is stated to be ~ 5-15%, and the recommended procedure is repeating fine-needle aspiration cytology (FNAC). [1] Similarly, the category IV thyroid nodules on BTCRS is designated as "Follicular Neoplasm or Suspicious for a Follicular Neoplasm", the malignancy rate of these is estimated to be around 15-30%, and the suggested management approach for these is surgical lobectomy. We, herein, compare and contrast the possible adjunct role of noninvasive molecular imaging features [combining fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT), ultrasound (US)-elastography, and diffusion weighted imaging-magnetic resonance imaging (DWI-MRI)] in the reported category III thyroid nodules in two cases, illustrating how they can enhance the confidence of diagnosis due to their negative predictive value.


   Case Report Top


The first case was a 65-year-old female who presented with mixed echogenicity, predominantly hyperechoic lesion measuring 6.1 cm × 3.9 cm, with central macrocalcification on grayscale transverse US [Figure 1]a], with internal vascularity and peripheral hallow. Ultrasonography (USG)-guided FNAC was suggestive of follicular lesion of undetermined significance (Bethesda category III) [Figure 1]b]. Split-screen B-mode US image (left) and US-elastogram (right) showed a focal stiff nodule (star) with predominantly maintained elasticity. The Rago and Asteria strain elastographic scores of the lesion were 3 and 2, respectively, which are suggestive of indeterminate nodule [Figure 1]c and d]. Plain axial MRI images showed heterogeneous signal intensity on T2-weighted (T2W) [Figure 1]c] and predominantly hypointensity on T1-weighted (T1W) images. The central dark hypointense area on both T2W and T1W images represents calcification (arrow) [Figure 1]e and f]. Diffusion colored maps of exponential apparent diffusion coefficient (eADC) and apparent diffusion coefficient (ADC) value obtained from the ADC map, with b-factor between 0 and 500. On elastogram (star), the ADC map showed low values in the area of stiffness that corresponds to restricted diffusion with a measured ADC value of 0.34 mm 2 /s × 10-3 mm 2 /s. The FDG-PET/CT [Figure 1]g] was predominantly negative, with very low grade FDG uptake in the nodule. A repeat FNAC is suggested for colloid nodular goitre with cystic changes.
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

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The second case, a 29-year-old female presenting with 2.3 cm × 1.4 cm solitary nodule of left lobe lower pole on grayscale transverse US showed a heterogeneous, predominantly iso to hypoechoic, lesion that measures 3.7 × 1.9 cm [Figure 2]a] and was cold on 99mTcO4 scintigraphy. The USG- guided FNAC was reported to be "Follicular Lesion of Undetermined Significance (Bethesda category III)" [Figure 2]b]. Split-screen B-mode US image (left) and US-elastogram (right) showed a predominant stiff nodule (star). The Rago and Asteria strain elastographic scores of the lesion were 3 and 3, respectively, [Figure 2]c and d]. Plain axial MRI images showed a predominantly iso-hypointense on both T2W and T1W images [Figure 2]e and f]. Diffusion colored maps of EADC and ADC value obtained from the ADC map with B-factor between 0 and 500. The ADC map of the left side nodule (star) showed a diffusion pattern similar to the normal parenchyma of the right lobe of thyroid with a measured ADC value of 1.82 mm 2 /s × 10-3 mm 2 /s, which represented an area of stiffness on elastogram. FDG-PET/CT [Figure 2]g] predominantly demonstrated the nodule to be FDG nonavid in a background of thyroiditis-like picture for the rest of the glands. A follow-up repeat FNAC at 3 months suggested chronic thyroiditis.
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

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The overall impressions by the interpreting physicians have been tablulated in [Table 1], along with the impression in gray scale USG.
Table 1: Final impression rendered by the interpreters of various molecular imaging modalities


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   Discussion and Conclusion Top


The primary aim of the Bethesda system for reporting thyroid cytopathology (BSRTC) reported in 2009 was to standardize the terminology for interpreting FNA specimens of the thyroid nodules. [1] In addition to the standardization and systematization, it was observed that its implementation in routine settings helped in improving the diagnostic accuracy, with higher rates of detection of malignancy despite lower rates of thyroidectomies. [2] The intermediate category nodules designated by BSRTC is a "gray zone" area where further enhancement of diagnostic confidence would aid in better management and reduce unnecessary procedures including thyroidectomies. [3]

The presented illustrations in this communication demonstrate the imaging features of the promising molecular imaging approaches and impressions rendered with each [Table 1], along with grayscale USG. The illustrations demonstrate the probable clinical utility that could be employed for characterizing these intermediate category nodules on USG-guided FNAC. [2] We hypothesize that their combined application could also be potentially extended to category IV ("Follicular Neoplasm or Suspicious for a Follicular Neoplasm") nodules as well, only around 15-30% of which turn out to be malignant. [1] This would, however, need to be examined in prospective studies encompassing both categories of the intermediate category (III and IV) nodules for defining their definitive place.

 
   References Top

1.
Cibas ES, Ali SZ; NCI Thyroid FNA State of the Science Conference. The bethesda system for reporting thyroid cytopathology. Am J Clin Pathol 2009;132:658-65.  Back to cited text no. 1
    
2.
Hirsch D, Robenshtok E, Bachar G, Braslavsky D, Benbassat C. The implementation of the bethesda system for reporting thyroid cytopathology improves malignancy detection despite lower rate of thyroidectomy in indeterminate nodules. World J Surg 2015. [Epub ahead of print].  Back to cited text no. 2
    
3.
Basu S. Employing Bayesian approach to the intermediate risk categories of the Bethesda thyroid cytopathology reporting system: Can FDG PET/CT find a strong enough evidence-base to be practised clinically as an adjunct? Eur J Nucl Med Mol Imaging 2014;41:2354-5.  Back to cited text no. 3
    


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1]


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