An unusually mobile kidney that descends toward the pelvis is known as what?

• A. Nephroptosis
• B. Hydronephrosis
• C. Polycystic kidney disease
• D. Ectopic kidney

Answer: (A)

Mobility of the kidney with downward movement is nephroptosis, often called a floating kidney. The kidneys are normally held in place by surrounding fat and fascia; when these supports are lax, the kidney becomes unusually mobile and may descend toward the pelvis when the person stands upright because gravity is pulling it downward. Imaging or positional changes may show the kidney moving several vertebral levels or centimeters between supine and upright positions, and some patients may have intermittent flank pain with standing.

This differs from hydronephrosis, which is dilation of the collecting system from obstruction or reflux; polycystic kidney disease, which features multiple cysts within the kidney; and an ectopic kidney, which is a congenital malposition of a kidney that never ascended to its normal position, not simply a mobile kidney.