From the Guidelines
Normal kidneys are typically not ballotable during physical examination, and large kidneys are not always ballotable either, as their palpability depends on various factors such as patient body habitus, abdominal wall thickness, and the degree of kidney enlargement. Ballottement is a technique where an organ is palpated by pushing it from one hand toward the examining hand, and normal kidneys are usually too small and positioned too deeply within the retroperitoneal space to be felt this way 1. According to the American College of Radiology, renal length correlates with height, sex, age, and weight in normal patients, and varies with the state of hydration or presence of an obstruction 1.
Key Factors Affecting Kidney Palpability
- Patient body habitus: obesity or a large amount of abdominal fat can make it difficult to palpate the kidneys
- Abdominal wall thickness: a thicker abdominal wall can reduce the ability to feel the kidneys
- Degree of kidney enlargement: significantly enlarged kidneys may be more easily palpable, but this is not always the case
- Position of the kidneys: the right kidney is generally easier to ballotte than the left due to its slightly lower position
Importance of Proper Patient Positioning
When performing kidney ballottement, the examiner places one hand posteriorly in the costovertebral angle and the other hand anteriorly below the costal margin, then applies gentle pressure to detect the kidney between the hands 1. This technique requires practice and proper patient positioning, typically with the patient lying supine or in a lateral decubitus position.
Limitations of Ultrasound in Evaluating Kidney Size
While ultrasound can be used to evaluate renal size and volume, it may not always be accurate, especially in patients with renal sinus fat or infiltrative disorders 1. Renal length <9 cm in an adult is definitely abnormal, but normal-sized kidneys do not exclude chronic kidney disease (CKD) as renal size is initially preserved in diabetic nephropathy or infiltrative disorders 1.
From the Research
Kidney Ballotability
- Normal kidneys are not typically ballotable, as they are firmly fixed in the retroperitoneal space and surrounded by perirenal fat [(2,3,4,5,6)].
- Large kidneys, such as those found in polycystic kidney disease (PKD), may be ballotable due to their increased size and altered anatomy [(3,4,5)].
- However, ballotability is not a definitive characteristic of large kidneys, and other factors such as the presence of cysts, fibrosis, or other renal pathologies can influence kidney mobility [(2,6)].
Factors Influencing Kidney Ballotability
- The presence of fluid-filled cysts, as seen in PKD, can affect kidney density and mobility, potentially making them more ballotable [(3,4,5)].
- Renal enlargement, as observed in hydronephrosis, can also impact kidney ballotability, although this is not always the case 2.
- The relationship between kidney size, cyst formation, and ballotability is complex and requires further study to fully understand the underlying mechanisms [(3,4,5)].