A Prospective Study to Evaluate the Reliability of Thyroid Imaging Reporting and Data System in Differentiation between Benign and Malignant Thyroid Lesions
Authors: Srinivas M Naren Satya , Amogh V N , Gautam Munnangi Satya , Prathyusha Ivvala Sai , Vikram N R , Retnam M Kamala , Balakrishna B V , Kudva Narendranath 
Published: February 2016

Objectives:
To evaluate diagnostic reliability of the daily use of thyroid imaging reporting and data system (TIRADS) classification proposed by Kwak et al., in differentiating between a benign and a malignant thyroid lesion, to calculate inter-observer variability in the interpretation of each of the TIRADS ultrasound features and to evaluate role of TIRADS system in reducing unnecessary biopsies of benign lesions.

Materials and Methods:
Three hundred and sixty-five patients with clinically suspected thyroid lesions during the period from November 1, 2011, to August 31, 2015, were prospectively scanned on gray-scale and Doppler imaging by six radiologists separately. We used GE VOLUSON 730 PRO machine (GE healthcare, Milwaukee, USA) equipped with a 7.5–12 MHz high-frequency linear array transducer with color and power Doppler capability. We evaluated five sonological features: Internal composition, echogenicity, margins, presence and type of calcification, and shape of the lesion. Based on the TIRADS proposed by Kwak et al., we determined categories of the thyroid lesions. The diagnostic performance of TIRADS classification system was evaluated by comparison with the fine-needle aspiration cytology (FNAC) reports which were subsequently obtained after taking informed consent from the patients. All follicular neoplasms on FNAC were further followed up with excision biopsy and histology. The cytopathological report was used as the standard final diagnosis for comparison. The P value and odds ratio were determined to quantify how strongly the presence or absence of a particular ultrasound feature was associated with benignity or malignancy in the study population. The risk of malignancy was stratified for each TIRADS category-based on the total number of benign and malignant lesions in that category. Cervical lymph nodes were also evaluated for their size, loss of the central, echogenic hilum, presence of irregular and indistinct margin, microcalcification, and necrotic changes. Cohen's Kappa coefficient was determined separately for each of the five TIRADS malignant features to study the inter-observer agreement. Furthermore, the percentage of benign cases that were accurately determined by TIRADS which could have avoided unnecessary FNAC was determined.

Results:
The risk of malignancy in TIRADS categories 1 and 2 was found to be 0%, 0.64% in category 3, 4.76% in category 4A, 66.67% in category 4B, 83.33% in category 4C, and 100% in category 5. Out of the five suspicious sonological features, irregular margins showed the highest positive predictive value (95.45%) for malignancy followed by taller than wide shape (92.86%), microcalcifications (66.67%), marked hypoechogenicity (54.55%), and solid composition (48.15%). The specificity of three sonological features (completely cystic structure, hyperechogenicity, and macrocalcification) in classifying a nodule as benign was 100%. Loss of central echogenic hilum, presence of an irregular and indistinct margin, microcalcification and necrosis were found to have sensitivity of 100%, 63.63%, 27.27%, and 9.09%, respectively and specificity of 95.7%, 98.5%, 100%, and 100%, respectively for cervical lymph node to be malignant. The Kappa value for taller than wide shape, microcalcification, marked hypoechogenicity, solid composition, and irregular margins was 1.0 (95% confidence interval [CI]: 1–1), 1.0 (95% CI: 1–1), 0.90 (95% CI: 0.82–1), 0.88 (95% CI: 0.77–0.92), and 0.82 (95% CI: 0.64–1), respectively. The estimated decrease in unnecessary FNACs was found to be 43.83–86.30%.

Conclusions:
TIRADS proposed by Kwak et al., combined with evaluation for sonological features of malignant lymph nodes is a valuable, safe, widely available, and easily reproducible imaging tool to stratify the risk of a thyroid lesion and helps in precluding unnecessary FNACs in a significant number of patients. TIRADS features convincingly show comparable results in the interpretation of TIRADS features more so, in the hands of radiologists experienced in thyroid imaging.