BACKGROUND: “Mirena” is a hormone eluting intrauterine device (IUD) which locally releases approximately 20 μg/day of levonorgestrel, a progestogen commonly used in contraceptive products. Though the contraceptive effect of Mirena is claimed to be local, elevated Levonorgestrel serum levels following Mirena insertion have been reported in the literature. Background parenchymal enhancement (BPE) on breast MRI is known to be influenced by hormonal status. The purpose of this study was to assess if the presence of a Mirena IUD affects BPE on breast MRI.
MATERIAL AND METHODS: This study was IRB approved. Due to the retrospective nature, the need for informed consent was waived. Clinical information was collected from the routine clinical patient questionnaire. Twenty-six patients who underwent breast MRI during a single year reported a Mirena IUD, these constituted the study group. An age matched group of 28 consecutive women who underwent breast MRI during the same year and reported no Mirena IUD and active menstrual cycle composed the control group. If a menstrual period was reported, the MRI examination was scheduled between day 5-14 of the cycle. MR images in both groups were reviewed to determine breast density (on T2W images) and BPE (on the first post contrast subtracted series and MIP). Statistical analysis was performed using the student t test with p
RESULTS: Patient age was similar in both groups ranging from 31-51yrs in the study group (ave 43; median 43) and 30-52 yrs in the control group (ave 41; median 42). In the control group all patients reported having a menstrual cycle whereas in the study group 58% reported a menstrual cycle. Breast density was mostly dense (ACR category 3 or 4) in 81% of the study group and 82% of the control group. BPE was significantly more increased in the study group with moderate or marked BPE found in 54% of the study group compared to 25% in the control group. This difference was found also within the subset of patients with dense breasts with 62% increased BPE in the study group compared to 30% in the control group. Within the study group, there was a slight trend for increased BPE in patients with absence of a menstrual cycle (63%) compared to those with a cycle (47%).
CONCLUSION: In patients with a Mirena IUD increased BPE on breast MRI is significantly more common. Further investigation is warranted to understand the mechanism of this effect.
