Medullary sponge kidney on axial computed tomography: comparison with excretory urography.

To evaluate features of medullary sponge kidney (MSK) on computed tomography (CT), 4-mm-thick axial slices without intravenous contrast material were first made in 13 patients through 24 kidneys which showed images of MSK on excretory urograms. On CT, papillary calcifications were found in eleven kidneys. In five of these kidneys, the calcifications were not detectable on plain films. Some hyperdense papillae (attenuation value 55-70 Hounsfield units) without calcification were found in four other kidneys. Nine kidneys appeared normal. Ten of these 24 kidneys were reexamined by a second series of 4-mm-thick axial slices, 5 min after intravenous injections of 50 ml of Urografin. Images suggesting possible ectasia of precaliceal tubules were found in only four kidneys. These images appear much less obvious and characteristic on CT than on excretory urogram and do nothing more than suggest the possibility of MSK. In conclusion, the sensitivity of CT in the detection of MSK is markedly lower than that of excretory urography. In the most florid cases of the disease, CT can only show images suggesting the possibility of MSK. On the other hand, CT appears much more sensitive than plain films and tomograms of excretory urography in the detection of papillary calcifications, the most frequent complication of MSK.