[The silent kidney. Evolving ultrasonic picture of emphysematous pyelonephritis: the vanishing kidney. Apropos of a case].

The authors report the progressive disappearing of the sonographical image of a previously visualized kidney in a case of emphysematous pyelonephritis. They have called the sonographic vanishing kidney "the sign of the Deaf Kidney". The non-visualisation of a kidney with advanced emphysematous pyelonephritis is due to the infiltration of the perirenal environment by a gas envelope and the filling of the excretory cavities by gas. The perirenal gas-bag forms a shield against ultrasonic waves. The sonographer must be aware of the eventuality of not being able to individualize a renal structure when wrapped in gas. He must then ask for a zonography of the renal area in order to confirm the gas-containing collection in the kidney.