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Background: Pyelolymphatic backflow phenomenon, which is a subtype of pyelorenal backflow, is a rare condition that occurs during the acute phase of urinary obstruction. Pyelorenal backflow has already been described in humans with retrograde pyelography. Our report presents a rare case of pyelolyphatic backflow demonstrated by a computed tomography. Case Report: A 67-year-old man with a history of bladder carcinoma was admitted to the emergency department due to right-sided flank pain and hematuria. Hematuria resolved after insertion of a 3-way urinary catheter, but flank pain persisted. As a result, an abdominopelvic CT was performed. CT revealed numerous tiny, serpiginous tubular structures connected with each other and filled with urine. They began intrarenally and extended caudally surrounding the ureter in the retroperitoneum. Subsequently, the patient underwent an ultrasound-guided nephrostomy to decompress the collecting system of the right kidney. Antegrade pyelography revealed minimal hydroneprosis. However, no leakage from the ureter to the retroperitoneum was observed, proving that the changes demonstrated by a CT were due to pyelolymphatic reflux caused by increased pressure in the collecting tubules filling the lymphatics with opaque urine. Conclusions: This report presents a very rare case of pyelolymphatic reflux demonstrated by a CT. We present this case report as a reminder that although rare, pyelolymphatic reflux can occur as a result of obstruction without manifestations of hydronephrosis and it can be confused with leakage from the ureter.