Report of a case of renal hilum Castleman disease complicated with Paget's disease of the breast.

Renal hilar Castleman disease is a rare lymphoproliferative disorder characterized by non-specific radiological manifestations. It is easily misdiagnosed as primary renal or adrenal malignant tumors in clinical practice, which may consequently lead to unnecessary radical nephrectomy. A 51-year-old female with a history of right breast cancer treated with mastectomy and adjuvant endocrine therapy 7 years prior presented with right nipple erosion. Biopsy confirmed Paget's disease, and preoperative staging with contrast-enhanced computed tomography (CT) incidentally revealed a solitary soft-tissue mass adjacent to the left renal hilum and abdominal aorta, with a maximum diameter of 8.5 cm × 6.2 cm and moderate heterogeneous enhancement. Strip-like and punctate calcifications were observed within the lesion, accompanied by reactive lymph nodes at the periphery and compression as well as displacement of the left renal vessels. The patient presented no specific clinical symptoms related to the retroperitoneal mass. According to comprehensive preoperative assessment and multidisciplinary consultation, the patient underwent complete radical resection of the renal hilar mass combined with left nephrectomy. Postoperative histopathological examination and immunohistochemical staining confirmed the diagnosis of hyaline-vascular type Castleman disease. The patient recovered uneventfully after surgery, and no local recurrence or distant metastasis was observed during the 12-month follow-up, with a favorable long-term prognosis. This case highlights the radiological difficulties in differentiating renal hilar Castleman disease from malignant renal tumors and emphasizes the necessity of standardized preoperative multimodal evaluation, which helps avoid excessive surgical intervention such as blind radical nephrectomy for unexplained retroperitoneal masses.