Validity of resistive index for the diagnosis of malignant ovarian masses

To evaluate the validity of resistive index (RI) in conjunction to the morphological appearances.

Prospective cross sectional survey of 37 females with adnexal masses was selected through non probability sampling admitted in Obstetrics units, in a private hosital from January 2009 to March 2010. All women underwent transabdominal and transvaginal ultrasound and ovarian masses were characterized as probably benign or possibly malignant on the basis of their sonographic appearance. The RI was calculated in every case and threshold RI of 0.40 was used to differentiate benign from malignant lesions. Later pathologic proof was obtained in every case. Validity of the RI was calculated considering the histopathology as gold standard.

Out of these 37 masses, 19 were morphologically benign and pathology revealed the same results. The RI was less than 0.4 in 3 of these cases. Eighteen lesions were morphologically either malignant (or indeterminate). On pathologic examination, 7 were benign 2 were nonneoplastic masses and 9 were malignant neoplasm. The RI was greater than 0.4 in 8 of these cases and was less than 0.4 in only 2 of the eight lesions. Sensitivity of the RI was 18.18% in diagnosing the malignancy whereas the specificity was only 84.61%. Positive predictive value of RI to differentiate benign from malignant lesions was only 33.33% and negative predictive value was 70.96%. Thus the accuracy of the RI was 64.86% with precision of only 33.33%.

Resistive index may improve specificity in characterizing malignant ovarian lesions on ultrasound but it can be misleading.