Is pain always present in patients with hydronephrosis?
The pain in obstruction of the upper urinary tract is a result of distention of the renal collecting system.
If obstruction and distention occur acutely, then pain can be excruciating and is often associated with nausea and vomiting.
However, if obstruction is slowly progressive, then the process can be painless (a.k.a. “silent” obstruction).