Significance of incidentally detected subcentimeter enhancing lesions on preoperative breast MRI: role of second-look ultrasound in lesion detection and management.

OBJECTIVE. The purpose of this article is to evaluate the clinical significance of subcentimeter enhancing lesions incidentally detected on preoperative breast MRI in patients with breast cancer and the role of second-look ultrasound in lesion detection and characterization. MATERIALS AND METHODS. From January 2010 through December 2010, 180 lesions measuring less than 10 mm incidentally detected on MRI in 108 women with second-look ultrasound examinations were included (mean patient age, 47.9 years; mean [± SD] lesion size, 5.56 ± 1.64 mm). Seventy-two (40.0%) lesions were smaller than 5 mm, and 108 (60.0%) were 5 mm or larger. Of the 180 lesions, 103 (57.2%) had been biopsied or excised by localization, and 77 (42.8%) with benign ultrasound features had been followed with ultrasound for at least 2 years. Clinical and imaging features were recorded for analysis. RESULTS. Of the 180 enhancing lesions detected on MRI, 14 (7.8%) were malignant and 166 (92.2%) were benign. The malignancy rate of lesions 5 mm or larger was higher than that for lesions smaller than 5 mm (10.2% vs 4.2%), without statistical significance (p = 0.344). The washout enhancement pattern was statistically significantly associated with malignancy (p = 0.032). Although malignant ultrasound features such as nonparallel orientation were more common in malignant lesions, most malignancies had benign features, including oval shape, parallel orientation, and circumscribed margins, with BI-RADS category 4a (n = 12; 85.8%) as the final assessment. CONCLUSION. Second-look ultrasound is a feasible method for evaluating MRI-detected subcentimeter sized lesions in preoperative assessment of patients with breast cancer. A lower threshold should be applied with consideration of MRI features in deciding whether to biopsy or excise these lesions.