Hydronephrosis is caused by obstruction downstream and what does it indicate?

• A. Obstruction downstream (stone, tumor, stricture) leading to dilation of the renal pelvis; indicates urinary outflow obstruction and requires evaluation
• B. Infection only
• C. Dehydration
• D. Low blood pressure

Answer: (A)

Hydronephrosis reflects a blockage in urine flow downstream of the kidneys. The obstruction creates back pressure that dilates the renal pelvis and calyces, which shows up as hydronephrosis on imaging. This indicates a urinary outflow obstruction and requires evaluation to find the cause—such as a stone, tumor, or stricture—and to prevent kidney damage from ongoing pressure. In contrast, infection alone, dehydration, or low blood pressure do not directly cause dilation of the collecting system from an obstruction.