A 72-year-old man with a history of a right renal cyst underwent Endoscopic Mucosal Resection (EMR) for polyps in the transverse and sigmoid colon. The patient developed a high fever the day after the resection. Blood tests revealed elevated levels of inflammatory markers, and computed tomography (CT) revealed the right renal cyst enlargement with wall thickening and increased attenuation of the surrounding fat tissue. Based on these findings, the patient was diagnosed with an infected renal cyst and was admitted to our hospital. The patient was successfully treated with antibiotics and underwent percutaneous cyst drainage. In the present case, mechanical injury to the renal cyst associated with colonic EMR was considered the most likely cause of infection. Infected renal cysts as complications of colonic EMR are extremely rare; therefore, we report the clinical significance of this case.
