A 59 year old previously healthy man presented to the emergency department with abdominal pain which began several hours earlier. The pain began in the lower quadrants and intensified throughout the day. He denied hematochezia, melena, or change in bowel habits. An abdominal CT scan showed free air, inflammation near the cecum, a right renal cyst and a left renal mass.

CT scan through the kidneys

1. What is your differential diagnosis?