IRC are rare entities characterized by fever and unilateral flank pain
resistant to antibiotic therapy. In our series of nine IRC in eight p
atients, the predominant sonographic finding was an abnormal echogenic
texture of the cyst contents, in contrast to previous reports that st
ressed the frequency of wall thickening as a sign of infection. Sonogr
aphically guided cyst aspiration and drainage of eight cysts in seven
patients provided diagnostic material and resulted in relief of sympto
ms. Although the cause of IRC is uncertain, these entities may be more
common than previously suspected.