Incidental detection of renomedullary interstitial cell tumour in a renal biopsy specimen

A 51-year-old woman with asymptomatic proteinuria and haematuria was admitted for a renal biopsy. Upon admission, her blood pressure was 118/68mmHg. Urinalysis revealed proteinuria 1þ, blood 2þ, but glucose-negative. A microscopic examination showed 0–1 white and 20–30 red blood cells per high power field. Laboratory investigations showed serum total protein 6.8 g/dl, albumin 4.3 g/dl, sodium 141mmol/l, potassium 3.8mmol/l, creatinine 0.4mg/dl, blood urea nitrogen 15.3mg/dl, creatinine clearance 114ml/min, 24 h urinary protein 0.43 g and haemoglobin 13.4 g/dl. An immunological screen and radiological studies were normal. A renomedullary interstitial cell tumour was identified in the medulla of a renal biopsy specimen (Figure 1). Glomeruli were mostly normal by light microscopy. Immunofluorescence studies were negative and electron micrography of glomeruli did not reveal dense deposits.