Hydronephrosis

Overview
  • Hydronephrosis is a possible complication of urinary tract obstruction characterized by dilation of the renal pelvis and calyces along with attendant atrophy of the renal parenchyma.
Etiology
Pathogenesis
  • Overview
    • Obstruction of the urinary tract can result in backup of urine into the renal parenchyma. Buildup of urine increases the urine's pressure within the kidneys, directly causing the following issues.
  • Renal Dilation and Atrophy
    • If obstruction develops insidiously and over time, slow dilation of the renal pelvis and calyces occurs. Increased pressure within the renal parenchyma also reduces blood flow to the kidneys, and thus the renal parenchyma atrophies over time.
  • Renal Dysfunction
    • The increased pressure within the kidneys disrupts proper processing of tubular fluid. Because the renal papillae are the first to be exposed to the increased pressure, the function of the late distal tubule and collecting duct is the first to be compromised. Dysfunction of this segment results in an inability to excrete a concentrated urine due to dysfunctional free water resorption (See: Late Distal Tubule and Collecting Duct Transport).
Morphology
  • Overview
    • The morphological features described here apply to those cases where obstruction and buildup of urine has not caused early clinical symptomology and has thus been allowed to occur over a long time period. In many cases, obstruction causes early clinical consequences and thus long-term morphological changes do not occur due to earlier clinical intervention (See "Clinical Consequences" below)
  • Gross Appearance:
    • Kidneys may be markedly enlarged and display enormous dilation of the renal pelvis and calyces. Additionally, renal pyramids may be grossly flattened and the entire kidney may be pale and atrophic appearance with a flattened renal cortex.
  • Histological Apperance
    • Morphological signs of atrophy first affect the collecting ducts while glomeruli are initially spared
    • Over time however, even glomeruli can become atrophied
Clinical Consequences
  • Overview
    • The extent of hydronephrosis largely depends on when overt clinical symptomology comes to light, initiating clinical intervention and thus correction of the urinary tract obstruction. The development of overt clinical symptomology depends largely on where the obstruction occurs.
  • Unilateral Obstruction
    • Might occur if a single ureter is obstructed (perhaps due to a renal and urinary tract stone). Severe obstruction in a single ureter is perhaps the worst possible situation as the other kidney largely compensates for any dysfunction in urine formation. Consequently, backup of urine and destruction of the obstructed kidney occurs silently for a long time period and may only manifest with flank pain.
  • Bilateral Obstruction
    • Occurs if obstruction occurs at the level of the bladder or urethra. Complete or severe obstruction will result in postrenal acute renal failure) and thus oliguria. Incomplete obstruction may paradoxically result in polyuria due to dysfunction of urinary concentrating ability of the late distal tubule and collecting duct (See pathogenesis section).