Methylene blue dye-related changes in the breast after sentinel lymph node localization

Objectives-The purpose of this study was to investigate the frequency and appearance of changes in the breast on sonography in patients after breast cancer surgery including sentinel lymph node localization using methylene blue dye. Methods-Three hundred thirty-seven consecutive patients who underwent breastconserving surgery in 2006 underwent breast sonography during 2 years after surgery. Sentinel lymph node localization using methylene blue dye was selectively performed. We retrospectively analyzed the unexplained focal lesions not at the lumpectomy site on sonography and investigated whether these findings were associated with sentinel lymph node localization. Results-Unexplained focal lesions were identified in 36 (14.1%) of 256 patients who had undergone sentinel lymph node localization. The lesions were in the periareolar region (n = 26; outer in 16, upper in 6, inner in 2, and lower in 2) or the retroareolar region (n = 10). The lesion appeared with a fat necrosis-like pattern in the subcutaneous fat layer in 24 (66.7%) or as an irregular mass in the glandular layer in 12 (33.3%). The unexplained focal lesions were pathologically proven benign (n = 10) or were improved or stable during 2 years of imaging follow-up after surgery (n = 26). The unexplained focal lesions in 2 (2.5%) of 81 patients without sentinel lymph node localization were in the nonareolar region, and 1 of these was a recurrence. Conclusions- After sentinel lymph node localization using methylene blue dye, breast sonography can show unexplained focal lesions in the periareolar and retroareolar regions. Although most of the changes suggest fat necrosis, an irregular parenchymal mass can develop and mimic a recurrence.