Contralateral Invasive Lobular Carcinoma Mimicking an Intramammary Lymph Node: A Case Report of MRI Detection and Elastography Differentiation in a Patient with Prior IDC

We report a rare case of contralateral invasive lobular carcinoma (ILC) diagnosed three years after initial treatment for invasive ductal carcinoma (IDC). The new lesion, detected incidentally on screening MRI, mimicked an intramammary lymph node on MRI and ultrasound due to its well-circumscribed appearance and hilar-like echogenicity. Shear-wave elastography revealed high stiffness values, raising suspicion for malignancy. Core biopsy confirmed ILC. This case underscores the critical role of MRI in detecting clinically occult cancers and highlights elastography’s potential to unmask malignancies mimicking benign structures.