Renal infection, including acute and chronic pyelonephritis, focal bacterial nephritis, renal and perinephric abscess, pyonephrosis and others, represents a spectrum of interrelated conditions. In recent years, computed tomography, ultrasound, nuclear scintigraphy, excretory urography (IVP) and magnetic resonance imaging have offered varying degrees of utility in evaluating renal infection. Although imaging in acute pyelonephritis has been extensively studied, this condition is a rare initial presentation as a renal cystic feature. This investigation presents a case of acute pyelonephritis, with an atypical initial imaging manifestation in renal cystic feature, which became a heterogeneous mass during follow up, and disappeared after treatment. Two conclusions can be drawn: first, a renal cystic lesion may be an initial presentation of acute pyelonephritis; secondly, the abnormalities of the ultrasonography imaging study of renal pyelonephritis persisted and progressed despite the improvement in clinical symptoms and laboratory findings, and displayed complete resolution of imaging abnormalities several months later.