An uncommon mimicker of renal malignancy: IgG4-related disease.

BACKGROUND: Increased usage of cross sectional imaging for a variety of indications, in particular CT imaging, has led to an increased detection of renal and ureteric masses. Benign ureteric masses are rare, with 95% of identified tumours consisting of transitional cell carcinoma (TCC). IgG4-related disease is a recognised clinical systemic autoimmune, inflammatory condition with a propensity for multi-organ manifestation. Nephritis and pseudo-tumour formation can occur when kidneys are involved. Ureteric involvement is more rare. CASE PRESENTATION: Forty nine-year-old Korean male was found to have an incidental invasive renal pelvis mass during investigation for chronic back pain and fatigue. Appearance of the tumour was consistent with an invasive malignancy, and consensus from multidisciplinary meeting was to have the tumour removed. Procedure involved a prolonged open surgery with reconstruction of contralateral renal blood supply and was complicated by a long recovery process. Final histopathology confirmed IgG4 renal pseudo tumour diagnosis. CONCLUSION: IgG4-related disease is a rare but potentially morbid disease that can mimic various cancers, including lung, pancreas and renal malignancies. A high index of suspicion is required to accurately diagnose this condition, through a targeted history taking, examination and investigation which should include biopsies. Failing to do so may result in unnecessary procedures being performed and exposing a patient to its associated risks.