Introduction to Impediments to Urine Flow



Introduction to Impediments to Urine Flow


Sanjay Jain, MD, PhD








This illustration depicts the different causes (urinary tract intrinsic or extrinsic) of impediments to urine flow. The lesions can arise anywhere along the path of urine flow, beginning in the kidney and extending through the ureters to the bladder and urethra. The major consequences on the kidney are obstructive or reflux nephropathy, which is manifested by dilation of the pelvis and calyces (hydronephrosis), loss of the medullary pyramids, and secondary atrophy of the cortex. These conditions increase the risk of urinary tract infection, which leads to further injury in the form of acute and chronic pyelonephritis.


TERMINOLOGY


Definitions



  • Impediment to urine flow: Retrograde or hindered urine flow due to obstructive or nonobstructive causes


  • Reflux: Retrograde urine flow from bladder into ureters or kidney due to functional or physical defects of lower tract


  • Hydronephrosis: Dilatation of renal pelvis due to functional or physical impediment of urine flow


  • Obstructive nephropathy: Damage to kidney due to obstruction


  • Reflux nephropathy: Damage to kidney due to urine reflux


CLASSIFICATION


Type of Impediment



  • Obstructive



    • Physical



      • Internal urinary system obstruction: Stones, tumors of urinary tract, infections


      • External compression of urinary system: Tumors, pregnancy, retroperitoneal fibrosis, endometriosis, crossing vessels


    • Functional



      • Ureter or collecting duct dysfunction


    • Congenital



      • Ureteropelvic junction obstruction (UPJO)


      • Primary obstructive megaureter or ureterovesical junction obstruction (UVJO)


      • Ureterocele


      • Posterior urethral valves (PUV)


    • Acquired


  • Nonobstructive: Vesicoureteral reflux (VUR)



    • Primary VUR


    • Secondary VUR



Region of Impediment and Associated Major Abnormalities



  • Upper urinary tract



    • Kidney (tubules, collecting duct)



      • UPJO


  • Lower urinary tract



    • Ureter



      • UPJO


      • UVJO or megaureter


      • Ureterocele


    • Bladder and ureter



      • VUR


    • Bladder and urethra



      • PUV


ETIOLOGY/PATHOGENESIS


Developmental Mechanisms



  • UPJO



    • Most common cause of obstructive nephropathy


    • Kidney



      • Abnormal water absorption or collecting duct cell function (functional obstruction)


      • Abnormal pacemaker function regulating peristalsis (functional obstruction)


    • Ureter



      • Abnormal ureter or pelvic wall development (increased extracellular matrix, disorganized smooth muscle) leading to defective peristalsis (functional obstruction)


    • Extrinsic



      • Crossing by lower pole renal vessels (physical obstruction)


      • Nervous system (pyeloureteral innervation) mediated defects in peristalsis (functional obstruction)


  • Megaureter



    • UVJO, abnormal muscular development or stricture, ureter insertion into bladder may be normal


    • Supernumerary ureters ectopically inserted into bladder


    • Refluxing megaureter due to primary or secondary reflux


  • Ureterocele



    • Distal blind-ending ureter often in completely duplicated collecting system


  • Primary VUR



    • Distal Wolffian duct (WD) &/or ureter maturation



      • Abnormal ureteric bud (UB) budding site


      • Failure of ureter insertion into bladder, abnormality of vesicoureteral junction


      • Failure of ureter to separate from WD


      • Abnormal common nephric duct (CND) degeneration


    • Most common congenital anomalies of kidney and urinary tract (CAKUT)



      • 50% of children with UTIs may have VUR


      • 15-34% of children with asymptomatic bacteriuria may have VUR


  • PUV



    • Failure of urogenital membrane disintegration


Genetic Mechanisms

Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Introduction to Impediments to Urine Flow
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