|LETTER TO EDITOR
|Year : 2017 | Volume
| Issue : 2 | Page : 131-133
Role of quantitative diffusion-weighted magnetic resonance imaging in differentiating benign and malignant thyroid lesions
Reddy Ravikanth1, Robert Patrick Selvam2, Denver Steven Pinto2
1 Department of Radiology, St. John's Medical College, Bengaluru, Karnataka, India
2 Department of Pathology, St. John's Medical College, Bengaluru, Karnataka, India
|Date of Web Publication||8-Jan-2018|
Dr. Reddy Ravikanth
Department of Radiology, St. John's Medical College, Bengaluru - 560 034, Karnataka
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Ravikanth R, Selvam RP, Pinto DS. Role of quantitative diffusion-weighted magnetic resonance imaging in differentiating benign and malignant thyroid lesions. J Curr Res Sci Med 2017;3:131-3
|How to cite this URL:|
Ravikanth R, Selvam RP, Pinto DS. Role of quantitative diffusion-weighted magnetic resonance imaging in differentiating benign and malignant thyroid lesions. J Curr Res Sci Med [serial online] 2017 [cited 2018 Jul 19];3:131-3. Available from: http://www.jcrsmed.org/text.asp?2017/3/2/131/222414
Diffusion-weighted imaging (DWI) is sensitive to changes in the microstructural organization of the tissue which affects the diffusion of water molecules and is commonly used in the diagnosis of central nervous system (CNS) infarcts and tumors. Apparent diffusion coefficient (ADC) values obtained from DWI can be taken as a quantitative parameter to assess malignant tumors from benign lesions of the thyroid. Quantitative diffusion-weighted magnetic resonance imaging (MRI) has the potential to serve as a great diagnostic tool in addition to thyroid sonography and ultrasound-guided fine-needle aspiration cytology (FNAC) for the characterization of thyroid nodules.
Ultrasound and FNAC are the first diagnostic investigations performed for the evaluation of thyroid lesions. Ultrasound is a noninvasive and sensitive imaging modality for the evaluation of thyroid lesions. However, there is still lack of reliable criteria for differentiating benign from malignant lesions of thyroid. FNAC samples are sometimes nondiagnostic or unsatisfactory, and a vast majority of FNAC recipients undergo thyroidectomy. DWI is an emerging technique and can be a promising tool in diagnosing malignancy of the thyroid. DWI is sensitive to changes in the microstructural organization of the tissue which affects the diffusion of water molecules and is commonly used in the diagnosis of CNS infarcts and tumors.
Thyroid sonography can be performed with a high-frequency linear transducer of 12 MHz with grey scale and power Doppler imaging and graded as Thyroid Imaging Reporting and Data System (TIRADS) categories. TIRADS is a risk stratification system of thyroid lesions proposed by Horvath et al. with a modified recommendation from JinKwak et al. and approved by American College of Radiology. TIRADS classification is as follows: TIRADS 1: Normal thyroid, TIRADS 2: Benign lesions, TIRADS 3: Probably benign, TIRADS 4: Suspicious lesions, TIRADS 5: Probably malignant, and TIRADS 6: Biopsy proven malignant. After grading the lesion, ultrasound-guided FNAC is performed from the suspicious lesions and histopathology examination is carried. The presence of coarse or rim calcifications increases the likelihood of malignancy almost twofold and presence of punctate calcifications increases the likelihood of cancer almost threefold.
Histopathology was regarded as the gold standard in evaluating thyroid lesions. Histologic analysis of the thyroid tissue structure and cellularity with H and E stain will be done by the pathologist. Cytopathology reports are graded as benign, indeterminate, suspicious for malignancy, malignant, and inadequate. Diagnosis of papillary carcinoma of thyroid is done by the microscopic visualization of psammoma bodies. However, psammoma bodies are present in only 40% of papillary carcinoma variant resulting in false-positive results. DWI with ADC values lesions help in differentiating benign and malignant lesions.
Diffusion-weighted MRI can be done with single shot or multiple shot techniques and is a relatively new and noninvasive technique to assess thyroid lesions. Diffusion-weighted images have to be acquired for different b-values 300, 500, and 800 s/mm 2. Good image quality is obtained with the use of b-value of 800 s/mm 2, high signal to noise ratio and small field of view on DWI. The ADC values obtained with b-values of 0 and 300 mm 2/s are significantly higher in benign lesions (benign ADC: 2.2 × 10-3 mm 2/s vs. malignant: 1.5 × 10-3 mm 2/s). Diffusion-weighted MRI at b-value 300 s/mm 2 [Figure 1]a with the corresponding ADC map [Figure 1]b of a lesion involving the left lobe of thyroid is shown demonstrating the benignity of the thyroid nodule. Diffusion-weighted image at b-value 800 s/mm 2 [Figure 2]a in a histopath proven case of colloid nodule with the corresponding ADC map [Figure 2]b is shown demonstrating the hyperintensity correlating with the high value on ADC. ADC map in a histopath-proven case of malignant nodule showed low ADC value (0.90 × 10 − 3 mm 2/s) in the lesion [Figure 3].
|Figure 1: (a) Axial Diffusion Weighted image at b-value 300 s/mm2 showing focus of restriction in the left lobe of thyroid (block area). (b) Apparent diffusion coefficient map showing corresponding hyperintensity of the focus suggesting a benign nodule with no true diffusion restriction (block area)|
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|Figure 2: (a) Axial diffusion-weighted image at b-value 800 s/mm2 in a histopathology proven case of colloid cyst of thyroid showing a well-defined lesion with restriction in the right lobe of thyroid (block area). (b) Apparent diffusion coefficient map demonstrating high-signal intensity correlating with a high value suggesting a benign lesion (block area)|
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|Figure 3: Apparent diffusion coefficient map showing low apparent diffusion coefficient value (0.90 B 10−3 mm2/s) in the lesion involving the right lobe of thyroid (arrow)|
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ADC maps have to be computed for b-values used in the DWI protocol and then compared. ADC values of tissues vary according to the cellularity and histopathology. In malignancies, the microscopic pathological changes cause reduction in extracellular space which limits the diffusion of water protons. Reduced ADC values are presented as high signal on DWI sequences. The previous studies have demonstrated that the ADC values of benign thyroid nodules may vary according to the complex composition within the nodule. Colloid deposition, necrosis, cystic changes, hemorrhage, fibrosis, and calcium deposition may occur within the nodule. ADC values were found to be the highest in cystic lesions of thyroid since they were made of serum or concentrated thyroglobulin. Conversely, the presence of calcifications may lead to decreased ADC values in papillary carcinoma of thyroid. Hence, DWI with the ADC values may be helpful in differentiating benign and malignant lesions of thyroid.
FNAC continues to be the cornerstone of thyroid nodule evaluation. FNAC is a simple, useful and cost-effective diagnostic procedure, but the evaluation of nondiagnostic and insufficient samples continues to be a problem, and there is no universally accepted approach to follow-up of nondiagnostic thyroid FNAC's. DWI is a noninvasive diagnostic method which can generate diffusion-weighted images and ADC maps. ADC values have been used as a quantitative parameter for differentiating benign and malignant lesions with high sensitivity. However, the drawbacks are MRI being an expensive investigation and areas of cystic degeneration in a malignant thyroid nodule may mimic a benign thyroid nodule. Quantitative diffusion-weighted MRI has the potential to serve as a great diagnostic tool in addition to thyroid sonography and ultrasound-guided FNAC for characterization of thyroid nodules.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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Conflicts of interest
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[Figure 1], [Figure 2], [Figure 3]