Hydronephrosis is the accumulation of urine in the kidney with subsequent distention and enlargement of the kidney. It results from an obstruction to the flow of urine from the kidney, through the ureter, to the bladder. Hydroureter is the accumulation of fluids in a ureter, resulting in its dilation and creates a near-irrebuttable presumption of hydronephrosis. The most common cause of hydronephrosis/hydroureter in both men and women is kidney stone blockage in the kidney (typically renal pelvis) or ureter. That said, physical forces external to the ureter (and much less likely, the kidney itself) that compress or torque it, can also cause a hydroureter (and resultant hydronephrosis). Such external forces include an enlarged prostate in men, compression of a ureter by an enlarging uterus in pregnancy. Less common causes of external compression of the ureter include enlarged organs, malignancies or other masses, and scar tissue (adhesions) which, again, either compress or torque the normal anatomy. Blood clots that create a blockage in the bladder or ureter may also cause hydronephrosis.
Regardless of the cause, though, when the blockage is acute, urine rapidly stagnates in the kidney, causing pain that is most commonly felt in the flank as referred pain. When the blockage develops over a longer course of time, hydronephrosis is insidious in that it may be so painless, mildly painless, or intermittently mild/moderately painless that it does not prompt the patient to appreciate that there is a medical problem with the potential for serious morbidity, e.g., loss of renal function and possible nephrectomy.
Hydronephrosis is an uncommon diagnosis in a young, healthy person. In most cases, it would be detected when a young person has pain from kidney stones, goes to an ER and has an ultrasound or CT scan of the abdomen and kidneys. Hydronephrosis needs to be considered in the differential diagnosis postoperatively to belly and pelvis surgery when a patient presents with certain kinds of pain and/or voiding issues.
No matter what the cause, the most urgent issue is to preserve kidney function before damage is irreversible. The accumulated urine in the kidneys creates high hydrostatic pressures that destroy the delicate tissue of the kidney (the glomeruli), leading to kidney failure.
Hydronephrosis medical expert witness specialties include urology, nephrology, pediatric nephrology, pediatric urology, renal pathology, pathology, radiology, emergency medicine, and pediatric emergency medicine.