Microvessel Maturation Correlates With Doppler Ultrasound Indices and Vascular Invasion in Follicular Thyroid Tumors

<h3>Background/Aim:</h3> Preoperative assessment of vascular invasion in follicular thyroid tumors remains challenging. Although quantitative Doppler indices, such as the resistive index (RI) and pulsatility index (PI), have been reported to be elevated in malignant tumors, their relationship with histological vascular characteristics is not fully understood. This study aimed to evaluate the association between Doppler indices and microvascular architecture, particularly microvessel maturation, and to assess their relevance to vascular invasion. <h3>Patients and Methods:</h3> Eighteen patients with follicular thyroid tumors who underwent preoperative Doppler ultrasonography followed by surgical resection were retrospectively analyzed. Based on histopathological findings, tumors were classified into vascular invasion-positive (n=4) and -negative (n=14) groups. Doppler parameters, including PI and RI, were measured in intratumoral vessels. Microvessel density (MVD) and microvessel maturation (MVMa), defined as the ratio of α-smooth muscle actin–positive vessels to CD31-positive vessels, were evaluated immunohistochemically. Group comparisons and correlation analyses were performed. <h3>Results:</h3> PI and RI tended to be higher in the vascular invasion-positive group, although the differences were not statistically significant. Angioinvasive tumors exhibited a greater difference between maximum and minimum flow velocities, suggesting altered intratumoral hemodynamics. MVD did not differ significantly between groups. In contrast, MVMa was significantly higher in the vascular invasion-positive group (<i>p</i>&lt;0.05). Furthermore, MVMa showed significant positive correlations with both PI and RI (<i>p</i>&lt;0.05 for both). <h3>Conclusion:</h3> In follicular thyroid tumors, increased RI and PI values are associated with enhanced microvessel maturation rather than microvessel density. These findings suggest that quantitative Doppler indices may reflect qualitative vascular properties and have potential as noninvasive imaging biomarkers for assessing vascular invasion.