Objective: This study aimed to estimate the frequency and timing of washout in a series of pathologically proven benign mass-like breast lesions at dynamic magnetic resonance imaging.
Methods: Institutional review board approval was obtained for this retrospective study. We evaluated enhancement kinetics of 33 pathologically confirmed benign breast lesions: fibroadenomas (n = 22), adenosis (n = 6), typical ductal hyperplasia (n = 2), fibroadenoma with ductal hyperplasia (n = 1), fibrosclerosis (n = 1), and inflammatory lesion (n = 1). Coronal 3-dimensional T1-weighted gradient-echo sequences were acquired before/after intravenous injection of 0.1 mmol/ kg gadoterate meglumine (time resolution, 111 seconds), 1 before and 5 after contrast injection. The time point at which the kinetic curve demonstrated a washout was recorded. Cumulative distribution of lesions showing washout was built. Paired comparisons of specificity for washout kinetics were performed using the McNemar test.
Results: Of 33 lesions, washout was never observed in 20 (61%), whereas 13 (39%) showed washout during the study. Of these 13 lesions, only 1 (inflammatory mass) exhibited washout within the first 3 minutes (specificity, 97%), 9 within 6 minutes (specificity, 73%), and 13 within 8 minutes (specificity, 61%). Specificity of washout kinetics within 3 minutes (97%) was significantly larger than that from the sixth minute (73%) and thereafter (P < 0.016).
Conclusions: A prolonged observation for dynamic breast magnetic resonance imaging may result in false-positive washout, especially after 6 minutes. Late washout should not be considered a reliable marker of malignancy.