Diagnostic dilemma of silicone-induced ipsilateral internal mammary lymphadenopathy mimicking breast cancer recurrence after mastectomy: a case report.

BACKGROUND: We present a patient with a history of mastectomy and breast reconstruction for breast cancer who was found to have ipsilateral internal mammary lymphadenopathy on diagnostic imaging performed for a benign contralateral breast abnormality. As newly identified lymphadenopathy in breast cancer patients may indicate metastasis requiring treatment, a comprehensive workup confirmed silicone-induced lymphadenitis, a rare inflammatory condition that closely mimics malignancy. The pathognomonic imaging findings are crucial for diagnosing silicone lymphadenitis. While relatively straightforward in accessible sites such as the axilla, detection proved challenging in intrathoracic nodes owing to overlying bony structures.

CASE PRESENTATION: An otherwise healthy, asymptomatic 79-year-old Caucasian woman with a history of left-sided breast cancer, treated 25 years ago with modified radical mastectomy, failed transverse rectus abdominis muscle flap reconstruction, and subsequent silicone implant-based reconstruction, underwent routine screening mammography. New lower outer quadrant densities were noted in the contralateral intact breast. Her medical, psychosocial, and family histories were not contributory. Magnetic resonance imaging with contrast revealed benign findings in the right breast and no changes in the reconstructed left breast. However, it identified two enlarged left internal mammary nodes. A positron emission tomography-computed tomography scan revealed mildly hypermetabolic left internal mammary lymph nodes raising suspicion for possible metastatic breast cancer. Diagnostic ultrasound demonstrated the pathognomonic "snowstorm sign," indicative of silicone uptake in draining lymph nodes due to extracapsular implant rupture. Magnetic resonance imaging and biopsy confirmed the presence of silicone within the affected nodes.

CONCLUSION: This case highlights the diagnostic challenge of silicone-induced lymphadenitis, which can mimic metastatic disease in breast cancer patients with implants. The "snowstorm sign" on ultrasound and noncontrast breast magnetic resonance imaging protocols are helpful for identifying silicone migration, while histopathology confirms the diagnosis. Distinguishing silicone-related inflammation from malignancy is essential to prevent unnecessary interventions and ensure appropriate management.