Detection of residual fibroglandular tissue on breast MRI and associated factors in women treated with mastectomy and DIEP flap breast reconstruction.

OBJECTIVES: This study investigates the frequency, extent and location of residual fibroglandular tissue (RFGT) on breast MRI after mastectomy and deep inferior epigastric perforator (DIEP) flap reconstruction. Possible risk factors for RFGT and the association with local breast malignancy after mastectomy (i.e. local recurrence or new primary tumour) are explored. MATERIALS AND METHODS: This retrospective, single-centre study included patients after mastectomy followed by DIEP flap reconstruction, who underwent breast MRI during follow-up between 2007 and 2022. Breast MRI exams were reassessed for the presence, diameter and location of RFGT. Relative risk was calculated to identify associated factors for RFGT. To investigate the possible association with malignancy after mastectomy, an explorative survival analysis was performed. RESULTS: Seventy-three patients were included (mean age 45 years, range 21-68), of which 66 were diagnosed with breast cancer. RFGT was detected in twenty (27.4%) patients, with a mean diameter of 13.5 mm (range 6-31), most frequently located in the upper outer quadrant of the breast. Tumour grade 3 seemed to be associated with increased risk of RFGT (RR = 2.7, 95% CI: 1.1-6.6, p = 0.050). After a median follow-up time of 110.0 months (range 14-354), malignancy after mastectomy had occurred in thirteen patients; this risk was non-significantly higher in patients with RFGT (HR = 2.3, 95% CI: 0.769-6.827, p = 0.137). CONCLUSION: RFGT is frequently detected on breast MRI after mastectomy and DIEP flap reconstruction. A baseline postoperative breast MRI exam could possibly be relevant to detect RFGT. The potential association with higher risk of malignancies after mastectomy warrants further investigation. KEY POINTS: Question research on RFGT detection after autologous reconstruction remains limited; therefore, this study investigates RFGT extent, location, risk factors, and association with malignancy. Findings RFGT could be detected on breast MRI in 27.4% of patients after DIEP flap reconstruction and might potentially be associated with an increased post-mastectomy malignancy risk. Critical relevance RFGT can frequently be detected on breast MRI following mastectomy and DIEP flap reconstruction and might be relevant for oncological safety. Future research is needed to validate this and assess the value of a postoperative baseline breast MRI for RFGT detection.