Accuracy of the Measurement of Uterine Leiomyoma by Transabdominal Ultrasonography

Introduction Uterine leiomyoma is a benign smooth muscle tumor. It does not necessarily require curative treatment, but if conservative management is chosen, it is important to rule out uterine leiomyosarcoma. When a size increase is observed, one must consider malignancy, and thus objective and cost-effective measurement of uterine size is important, especially for early detection of malignant change. Although MRI imaging is thought to be the gold standard for the diagnosis of uterine leiomyosarcoma, frequent MRI is impractical because of the incidence of uterine leiomyoma and the economic burden in real-world clinical practice. On the other hand, ultrasonography (US) is considered the most useful device in the observation of size changes. So this study aimed to examine the accuracy of the measurement of transabdominal US compared to MRI imaging. Materials and methods This retrospective study included 92 patients with uterine myoma ≥ 50 mm who undertook an MRI within 30 days after the transabdominal US. The longest diameter of the largest myoma (a), the longest diameter perpendicular to a in the sagittal image (b), and the longest diameter perpendicular to a and b in the axial image (c) were measured by US and MRI, and these were used to calculate the volume. Results were analyzed by intraclass correlation coefficient (ICC) 3.1. Results The ICC for the volume and major axis of the largest myoma by US and MRI were 0.87 and 0.90, respectively. The 95% confidence intervals (CI) were 0.82-0.91 and 0.87-0.93, respectively. Both reliability levels ranged from good to excellent. ICC was 0.54 (95%CI 0.15-0.78) in myomas with a volume of >500 cm³, and the concordant rate between US and MRI was poor to good. On the other hand, ICC was 0.82 (95%CI 0.57-0.93) even though all myomas with major axes greater than 120 mm had a volume >500 cm³, and the concordant rate between US and MRI measurements was moderate to excellent. In the evaluation by major axis, ICC was 0.60 (95%CI -0.41-0.95) for myomas larger than 160 mm, indicating a lower concordant rate. Conclusion Transabdominal US is an appropriate modality as well as MRI for follow-up of uterine myoma size if the nodules are 160 mm or smaller. Measurement of the major axis is easier and more useful than volume.