Matrix stone.

Matrix stone is a rare form of renal calculi, and it is often difficult to make an exact preoperative diagnosis. To our knowledge, we reported the first case of matrix stones which received magnetic resonance imaging (MRI) for image study. They showed hypointense signal in T1-weighted images and slight hyperintense signal in T2-weighted images. No obvious contrast enhancement was found after gadolinium administration in T1-weighted images. Besides, postoperative study of computerized tomography (CT) for matrix stones also showed the characteristic of soft tissue densities by measuring the Hounsfield units. We think our experiences may provide some help for the diagnosis of matrix stones when someone encounters the same situation and may prevent overtreatment due to misdiagnosis as malignancy.