A 57-year-old male is admitted to the hospital for a suspected kidney infection (likely pyelonephritis). The patient is placed on intravenous antibiotic therapy but continues to have a temperature of 103degF after 3 days of therapy. The urine culture grows lactose fermenting GNB which is pan drug sensitive On examination, he appears ill and has marked left flank tenderness. Ultrasound depicts the following finding What is the most likely diagnosis?