Background parenchymal enhancement in pregnancy-associated breast cancer: a hindrance to diagnosis?

PURPOSE: The purpose of this study is to investigate the detectability of pregnancy-associated breast cancer (PABC) in lactating glandular tissue on magnetic resonance imaging (MRI) by using pre- and post-contrast acquisitions and their derived postprocessed images and compare these results to ultrasound (US) and mammography (MG).

MATERIALS AND METHODS: We reviewed the electronic database for women with PABC and existing breast MRI. MR images (T2-weighted short inversion-recovery sequence [STIR], dynamic contrast-enhanced T1-weighted gradient echo sequence and postprocessed subtraction images [early post-contrast minus pre-contrast]) were retrospectively evaluated (image quality, parenchymal/tumour enhancement kintetics, tumour size and additional lesions). Supplemental subtraction images (latest post-contrast minus early post-contrast) to reduce plateau enhancement were additionally calculated and tumour conspicuity and size were measured. Findings were compared to US and MG reports.

RESULTS: Nineteen patients (range 27-42 years) were included. Background parenchymal enhancement (BPE) was minimal (n=1), mild (n=3), moderate (n=7) and marked (n=8) with kinetics measured plateau (n=8), continuous (n=10) and not quantifiable (n=1). Tumour kinetics presented wash-out (n=17) and plateau (n=2). Eighteen of nineteen tumours were identified on the supplemental subtraction images. All tumours were visible on US; 12/19 were visible on MG (63.2%). MRI detected additional malignant lesions in two patients.

CONCLUSION: Despite high BPE of the lactating breast, MRI securely detects carcinomas and identifies satellite lesions. By using supplemental subtraction images, background enhancement can be eliminated to facilitate diagnosis. US remains a reliable diagnostic tool, but additional MRI is recommended to rule out satellite/contralateral lesions. MG interpretations can be difficult due to high parenchymal density.

KEY POINTS: • Despite high background enhancement, MRI of the breast confidently detects carcinomas and identifies further lesions in the lactating breast. • By using supplemental subtraction images, background enhancement in the lactating breast can be eliminated to facilitate diagnosis. • US remains a reliable diagnostic tool. Mammography can be limited due to extremely dense breast tissue related to lactation.