Obstructive Nephropathy



Obstructive Nephropathy


Sanjay Jain, MD, PhD

Helen Liapis, MD










The typical features of chronic obstruction include dilation of the pelvis and calyces (hydronephrosis) image, loss of the medullary pyramids image, and secondary thinning of the cortex image.






A section of the medulla from a child with UPJO shows dilation of the larger medullary collecting ducts image due to increased urine back-pressure. The cortex is relatively spared image.


TERMINOLOGY


Definitions



  • Obstructive nephropathy



    • Damage to kidney due to urine flow obstruction


  • Hydronephrosis



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


ETIOLOGY/PATHOGENESIS


Causes



  • Physical obstruction



    • Stone


    • Tumors of the urinary tract



      • Prostate, bladder, ureter


    • Benign prostate hyperplasia (BPH)


    • External compression (tumors, pregnancy, retroperitoneal fibrosis, endometriosis, crossing vessels)


  • Functional obstruction



    • Developmental anomalies: Posterior urethral valves (PUV), ureterocele, ureteropelvic junction obstruction (UPJO), primary megaureter



      • UPJO is most common cause of obstructive nephropathy


Pathophysiology



  • Impediment to urine flow causes increase in back-pressure into collecting system and tubules


  • Increased back-pressure and retention of urine causes dilatation of collecting system and alterations in transporters and channels


  • Compression of renal parenchyma accompanies vascular compromise and inflammatory response


  • Cellular changes in interstitium and nephrons lead to varying degrees of scarring


  • Intrauterine obstruction during nephrogenesis can cause renal dysplasia


Animal Models



  • Unilateral ureteral obstruction (UUO)



    • Commonly used in rodents, marsupials


  • Genetic models



    • Provide evidence for functional defects rather than physical causes of obstructive nephropathy (Aqp2 mutations)


CLINICAL ISSUES


Presentation



  • Acute obstruction



    • Flank pain, nausea, and vomiting


    • Renal failure if bilateral


  • Chronic obstruction



    • Recurrent episodes of pyelonephritis


    • Hypertension


    • Renal failure if bilateral


Treatment



  • Surgical repair


  • Decompression


Prognosis



  • Prognostic criteria for congenital impediments to urine flow are not well defined; therefore, management criteria are debatable


  • Kidney failure may ensue if accompanied by dysplasia due to congenital obstruction


  • Correction of congenital obstruction may not resolve kidney damage; children should be followed into adulthood


  • High propensity to develop renal insufficiency in PUV patients


IMAGE FINDINGS


Ultrasonographic Findings



  • Dilated pelvis



MACROSCOPIC FEATURES


General Features



  • Dilatation of pelvis (hydronephrosis), blunting of calyces


  • Compression of the cortex


  • Irregular kidney surface due to scarring


  • Other anomalies or syndromes may be present: Hydronephrosis, small kidneys, duplicated collecting system, megaureter, hydroureter, dysplastic kidneys


  • Compensatory hypertrophy in contralateral kidney


MICROSCOPIC PATHOLOGY


Histologic Features



  • Glomeruli



    • Glomeruli relatively spared but eventually become globally sclerotic



      • Periglomerular fibrosis prominent


      • Global glomerulosclerosis, obsolescent glomeruli, glomerular cysts


      • Atubular glomeruli (cystic dilation of Bowman space)


    • Crescents seen rarely


    • Increased glomerular size in contralateral kidney


  • Tubules



    • Tubular atrophy, apoptosis


    • Thyroidization of tubules (end-stage atrophy)


    • Microcystic dilatation of distal nephron segments


    • Dilation of tubules may be more prominent in subcapsular collecting ducts


    • Rupture with leakage of Tamm-Horsfall protein


  • Interstitium



    • Fibrosis, diffuse


    • Mononuclear inflammation, plasma cells


    • Sometimes intense in sites of tubular rupture


    • Presence of cartilage or smooth muscle indicative of dysplasia



      • Segmental (lobar) or zonal (outer cortex) distribution


  • Vessels



    • Arterial medial hypertrophy and intimal fibroelastosis are indicative of hypertension


  • Pelvis and ureter



    • Pelvic dilatation, papillae effacement


    • Hypertrophy and dilation of ureter


    • Chronic inflammation mucosa of pelvis and ureter


Acute Obstruction



  • May have few pathologic findings


  • Interstitial edema, mild inflammation


  • Dilation of subcapsular collecting ducts


  • Dilated lymphatics contain Tamm-Horsfall protein

Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Obstructive Nephropathy
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