Which finding helps differentiate an enlarged kidney from an enlarged spleen in a patient with a left-sided abdominal mass?

The ability to identify normal tympany over the area helps in differentiating an enlarged kidney from an enlarged spleen due to the anatomical location and normal positioning of these organs in the abdomen, as well as the typical findings on physical examination. In the case of an enlarged spleen, it often displaces the stomach, potentially leading to a dullness upon percussion due to the solid organ's shape and the modification of the surrounding structures. In contrast, the kidney, being more posterior and having a less pronounced physical effect on adjacent structures when enlarged, often allows for tympany to persist as it does not directly affect the air-filled intestines that would cause dullness.

Understanding the characteristics of the spleen versus the kidney aids clinicians in performing an accurate assessment. Therefore, when normal tympany is detected in the presence of an abdominal mass, it suggests that the mass is less likely to be from an enlarged spleen or another solid organ and may indicate the presence of an enlarged kidney.