A slowly growing flank mass

CASE PRESENTATION A 62-year-old woman presented to her family physician with a twomonth history of a slowly growing left flank mass. She was previously well except for recurrent urinary tract infections; there was no recent travel or trauma. An ultrasound demonstrated a benign-appearing left renal cyst. Three weeks later, she began to develop flank pain, fevers, chills, night sweats and erythema of the skin over the flank mass. Cultures were not obtained at this time, and she was treated empirically with oral cloxacillin 500 mg four times daily for six weeks with minimal improvement. She developed nausea and vomiting with food consumption, and a 15 kg weight loss. One month later, the flank mass broke through the skin and began to drain serosanguinous fluid (Figure 1). Review of systems and physical examination were otherwise unremarkable. Initial laboratory investigations demonstrated a normocytic anemia (hemoglobin level 115 g/L), leukocytosis (white blood cell count 15.4×109/L), elevated inflammatory markers (C-reactive protein level 171.0 mg/L and erythrocyte sedimentation rate 85 mm/h) and a normal creatinine level (71 μmol/L). Computed tomography imaging (Figure 2) revealed a large mass involving the left kidney, encasing other organs on the left side of the abdomen and protruding through the flank. A computed tomography-guided biopsy of the left renal mass was performed.