The authors are hereby presenting a rare case of neoformation developing on the left kidney in a 80-year-old patient affected by left lumbar backache. The neoformation appears doubtful in nature, on ultrasonography, CT scan and MRI. The lesion is roundish and contiguous at the kidney convex edge; due to its clinical aspects, it requires a surgical management and is, therefore, easily excised. The histopathologic examination confirms it is a mesothelial cyst. The case is presented for its absolute rarity and for the preoperative diagnostic doubts it may generate.
