IgG4-related kidney disease mimicking renal cell carcinoma: a case report and literature review

IgG4-related kidney disease (IgG4-RKD) presenting as renal masses is a very rare clinical entity. IgG4-RKD represents the renal manifestation of IgG4–related disease (IgG4-RD) and is characterized primarily by tubulointerstitial nephritis (TIN) caused by infiltration of IgG4-positive plasma cells in the renal interstitium and tubules. Typical imaging findings include renal enlargement and cortical low-density lesions; however, a very small proportion of IgG4-RKD cases may present as space-occupying renal lesions, which are easily misdiagnosed as renal malignancies. In this report, we describe a patient hospitalized for a respiratory disease whose abdominal computed tomography (CT) scan (non-contrast, contrast-enhanced, and 3D reconstruction) revealed a space-occupying lesion in the right kidney, with no significant abnormalities in the left kidney. Clinicians initially suspected a malignant renal tumor and proceeded with radical nephrectomy of the right kidney. Postoperative histopathology and immunohistochemistry confirmed the diagnosis of IgG4-RKD.