Clinically, we know that it can present with anuria/oliguria, sudden onset of renal failure in the right context, hyperkalemia and hyponatremia.
There are clinical situations that can lead to a hydronephrosis that might not be apparent on imaging due to the mass effect from underlying disease state not letting any room for the kidney to expand.
1. Retroperitoneal Fibrosis
2. Cervical Cancer( classically described)
3. Any cancer with RP mets and severe carcinamatosis and mass effect.
Anyone else can think of other causes, chime in!