Images in Breast Oncology: Extra-Nodal Rosai–Dorfman Disease Mimicking Metastatic Breast Malignancy on PET CT

Rosai–Dorfman disease is a rare disorder wherein there is excessive production and accumulation of histiocytes in the lymph nodes. This excessive deposition may occur in other areas like the skin, central nervous system, kidney, and digestive tract. Also referred to as extra-nodal RDD, these may mimic other diseases in these organs. A postmenopausal lady was referred to us for breast biopsy from another centre. PET CT images taken already were concerning for metastatic breast malignancy. Rosai–Dorfman disease was diagnosed on histopathology based on samples taken from the right breast mass. This case highlighted the rare occurrence of Rosai–Dorfman disease affecting breast and mimicking a metastatic breast primary in the presence of loco-regional nodal disease and numerous lytic lesions in the bone.