Evaluation of the intramammary distribution of breast lesions detected by MRI but not conventional second- look B-mode ultrasound using an MRI/ultrasound fusion technique

Abstract The objective of this study was to evaluate the intramammary distribution of MRI-detected mass and focus lesions that were difficult to identify with conventional B-mode ultrasound (US) alone. Consecutive patients with lesions detected with MRI but not second-look conventional B-mode US were enrolled between May 2015 and June 2023. Following an additional supine MRI examination, we performed second-look US using real-time virtual sonography (RVS), an MRI/US image fusion technique. We divided the distribution of MRI-detected mammary gland lesions as follows: center of the mammary gland versus other (superficial fascia, deep fascia, and atrophic mammary gland). We were able to detect 27 (84%) of 32 MRI-detected lesions using second-look US with RVS. Of these 27 lesions, 5 (19%) were in the center of the mammary gland and 22 (81%) were located in other areas. We were able to biopsy all 27 lesions; 8 (30%) were malignant and 19 (70%) were benign. Histopathologically, three malignant lesions were invasive ductal carcinoma (IDC; luminal A), one was IDC (luminal B), and four were ductal carcinoma in situ (low-grade). Malignant lesions were found in all areas, with no statistical differences in frequency between the center of the mammary gland and other areas (p = 0.601). In this study, 81% of the lesions identified using second-look US with RVS were located outside the center of the mammary gland. Thus, we consider it important to carefully examine other areas for breast lesions when performing second-look US when a lesion has been detected with MRI but not with second-look conventional B-mode US.