Primary hyaline vascular Castleman disease of the kidney: case report and literature review.

Background: Castleman's disease (CD) is an uncommon type of benign proliferation of the lymphoid tissue, characterized by local or systemic lymphadenopathy that most frequently appears in the mediastinum; involvement of the kidney is uncommon, and proliferation originating from the kidney is extremely rare. Herein, we report a rare case of hyaline vascular Castleman's disease (HV-CD) in a 56-year-old male patient and discuss its morphological characteristics and differential diagnoses including mantle cell lymphoma (MCL), follicular lymphoma (FL), and nodal marginal zone lymphoma (NMZL).

Case presentation: A right upper-middle renal mass was detected after physical examination in a 56-year-old man without any clinical symptoms and a previous partial resection of the right kidney. Microscopically, the lymphoid follicles were increased in number and had expanded mantle zones and atrophic germinal centers. Vascular proliferation and hyalinization in the interfollicular zones were observed. Immunohistochemical staining showed CD20-positive cells in the mantle zones; CD21 and CD35 were expressed in the dendritic cells, CD3 was positive in a small number of T cells, and CD38 and CD138 were positive in the plasma cells. Additionally, Ki-67 expression was positive in the follicle centers. In contrast, staining for Bcl-2 in the germinal centers and cyclin D1 were negative. The immunohistochemical analysis combined with the morphological results supported the diagnosis of HV-CD. The patient recovered well after surgery.

Conclusions: Primarily renal HV-CD without lymph node hyperplasia or clinical symptoms is extraordinarily rare and different from the multicentric-type CD (MCD) with kidney involvement. Therefore, it is extremely important to improve the awareness of this diagnosis. Attention should be paid to the difference between HV-CD and common lymph node reactive hyperplasia, MCL, FL, NMZL, and so on. To avoid misdiagnosis as a renal malignant tumor requiring radical resection, distinguishing these diseases is crucial.