Resistance to blood flow in ovarian tumors: Correlation between resistance index and histological pattern of vascularization

Objective. To investigate the correlation between the histological patterns of vascularization and the resistance index (RI) in ovarian tumors. Design. In a retrospective study, the histological sections of the ovarian tumors with known preoperative RI values were reviewed and the pattern of vascularization was studied. Subjects. Twenty-two women underwent B-mode sonography and color Doppler ultrasound within 3 days prior to explorative laparotomy for ovarian masses in the years 1992-93. Methods. The RI of the ovarian tumors was calculated as the mean of three consecutive waveforms with the lowest RI. The representative histological sections were evaluated for quantity of arterioles and venules, after staining by Masson trichrome and Elastic Van Gieson. The arteriolar fraction (defined as the number of arterioles divided by the sum of the arterioles plus venules) and the density of vessels (defined as the number of arterioles and venules per microscopic field) were calculated in each histological section and correlated with the preoperative RI values. Results. The mean RI was 0.36 ± 0.07 for malignant tumors and 0.57 ± 0.03 for benign tumors. Ovaries with malignancies showed significantly lower arteriolar fraction values (0.30 ± 0.12) than those with benign tumors (0.56 ± 0.05) and those with metastatic tumors (0.43 ± 0.02) (p < 0.002 and p < 0.001, respectively). The density of vessels was higher in malignant tumors (8.0 ± 3.8) than in benign lesions (2.7 ± 1.5) (p < 0.01). RI values showed a strong positive correlation (r = +0.85, p < 0.0005) with the arteriolar fraction and a negative and weaker correlation (r = -0.69, p < 0.001) with the density of vessels. Conclusions. RI values are predominantly determined by the proportion of arterioles. The correlation between the histological pattern of vascularization and RI values reflects tumor angiogenesis and increases understanding of the advantages and limitations of measuring vascular resistance by color Doppler ultrasound.