Endocrine Abstracts

Objective: To assess the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of sonographic index point and resistivity index in predicting the risk for malignancy in thyroid nodules.

Methods: Fifty consecutive patients undergoing thyroid ultrasound for clinical nodular thyroid diseases prior to planned surgery were recruited for the study. Sonographic index point was calculated for each nodule using morphological characteristics (margins, shape, echogenicity, echostructure and nature of calcification) as a score. Spectral analysis was performed from the region showing maximum colour flow on 1 to 3 arteries of greater calibre in each nodule. Resistivity index (R.I) was recorded as an average of indices obtained. Sensitivity, specificity, PPV and NPV was obtained for sonographic index points and resistivity index for their ability to differentiate benign form malignant nodule using the post-operative histopathology report as the gold standard.

Results: There were 16 (5M/11F) malignant lesions and 34 benign lesions (4M/34F) among the study patients. The sonographic index points for malignant nodules were in the range of 3–8 and for benign lesions 1–7. The sonographic index point at a cut off value of >2 had a sensitivity of 93.7%, specificity of 75.3%, PPV of 15.7% and NPV of 98.4% in differentiating malignant from benign nodule. Using resistivity index at a cut off value of 0.75 showed sensitivity of 81.5%, specificity 92.3%, PPV 95.6% and NPV of 70.5%. A combination of both the indices had a sensitivity of 89.2%, specificity of 92.3%, PPV of 97%, NPV of 75% and diagnostic accuracy of 90%.

Conclusions: Sonographic index point had high sensitivity and with a high negative predictive value for diagnosing malignant nodules despite poor specificity. In combination with the Resistivity index there was improvement in the specificity with some loss of sensitivity but with a diagnostic accuracy of over ninety percent.