Causes and effects of hydronephrosis.
Urinary obstruction is a common cause of renal dysfunction. It is important to recognize because many of its causes are treatable. The effects of obstruction depend mainly on whether one or both sides are affected. Urinary obstruction produces distention of the renal pelvicaliceal system that is called hydronephrosis.
Obstruction of one side is commonly due to pathologic processes proximal to the urinary bladder (Figure 50-1). These result in hydronephrosis and may cause atrophy and loss of function of one kidney but do not cause renal failure. The causes include the following:
Ureteropelvic Junction Obstruction
This is a common disorder. While a few patients have an anatomic obstruction—most commonly an aberrant renal artery compressing the upper ureter—most cases are idiopathic (idiopathic hydronephrosis). In these patients, there is functional obstruction at the ureteropelvic junction with a patent lumen. Congenital abnormalities of the ureteropelvic musculature or innervation have been suggested as being the cause, and surgical removal of this region with reanastomosis results in cure. The obstruction is severe, and there is progressive dilation of the renal pelvis (hydronephrosis) above the ureteropelvic junction. The ureter is normal. The effects on the kidney vary. In patients with a renal pelvis that is extrarenal, massive dilation produces a huge cystic mass at the renal hilum that may present as an abdominal mass. In these cases the increase of pressure in the kidney is less than when the pelvis is intrarenal, and distention causes enlargement of the pelvicaliceal system, leading to renal atrophy (Figure 50-2).
Idiopathic hydronephrosis, showing marked dilation of renal pelvis and caliceal system. The kidney has been sectioned longitudinally in the plane of the dilated renal pelvis.
Congenital Diseases of the Ureters
Other congenital anomalies of the ureters may cause unilateral hydronephrosis. These include double ureter, bifid ureter, and abnormalities in ureteral muscle causing increased wall thickness (megaureter). A ureterocele is a cystic dilation of the terminal part of the ureter caused by congenital stenosis of the ureteral orifice in the bladder wall. The cystic terminal ureter commonly protrudes into the bladder lumen. While these ureteral abnormalities may present in childhood, many of them are either found incidentally or produce symptoms in adult life.
Acquired Diseases of the Ureters
These are common and include (1) luminal obstruction due to calculi, blood clots, or sloughed necrotic renal papillae; (2) mural causes such as fibrous strictures and neoplasms; and (3) extrinsic compression of the ureters in retroperitoneal fibrosis and retroperitoneal neoplasms.