Classification of Cystic Diseases



Classification of Cystic Diseases


Helen Liapis, MD

Joseph Gaut, MD, PhD








Adult ADPKD kidneys are massively enlarged and contain numerous oval/spherical cysts dispersed throughout the cortex and medulla. Cysts are lined by thin walls; some contain hemorrhagic fluid image.






Early onset ADPKD in a young child shows oval cysts varying in size, filled with turbid gelatinous fluid image. Overall size of the kidney is moderately large for age.


PATHOGENETIC CLASSIFICATION


Definition



  • Renal diseases characterized predominately by cysts



    • Cyst: Closed cavity in a previously noncystic structure



      • Cysts may arise in any part of nephron, but most frequently in tubules


      • Cysts may be found in renal cortex, medulla, or both


      • Cysts may be diffuse, focal, unilateral, or bilateral


      • Bilateral cysts are most commonly hereditary


      • Cysts can be randomly or uniformly distributed (e.g., along corticomedullary junction)


      • Sometimes ectasia is present rather than a closed cyst


    • Cysts arising in glomeruli are called glomerular cysts


    • Term “polycystic” should only be used for autosomal dominant and autosomal recessive polycystic kidney disease (ADPKD, ARPKD)


    • Location and shape of renal cysts are important for classification


    • No universally accepted classification scheme


    • Features considered



      • Genetic basis


      • Cystic anatomic structure (tubule, glomerulus, other)


      • Distribution of cysts (cortex, medulla)


Categories



  • Hereditary cystic diseases



    • Autosomal dominant polycystic kidney disease (ADPKD)


    • Autosomal recessive polycystic kidney disease (ARPKD)


    • Medullary cystic kidney disease (MCKD)


    • Nephronophthisis (NPH)


    • Tuberous sclerosis (TSC)


    • von Hippel-Lindau (VHL) disease


    • Primary glomerulocystic kidney disease (GCKD)


  • Acquired cystic diseases



    • Secondary GCKD


    • Acquired cystic disease (end-stage kidney)


    • Medullary sponge kidney


    • Multilocular renal cyst


    • Simple cortical cyst


  • Non-nephron renal cystic diseases



    • Pyelocalyceal diverticula


    • Perinephric pseudocyst


    • Lymphangiectasis/lymphangiomatosis


EPIDEMIOLOGY


Incidence



  • ADPKD: 1 in 500 live births


  • ARPKD: 1 in 20,000 live births


  • NPH: 1 in 8,000,000 in USA, 1 in 50,000 in Canada


  • TSC: 1 in 10,000-15,000 live births


ETIOLOGY/PATHOGENESIS


Histogenesis



  • Cystogenesis: Process involving aberrant formation or maintenance of a normally noncystic structure


  • Causes of tubular cysts



    • Epithelial cell proliferation


    • Apoptosis and defective clearance of apoptotic cells causing tubular obstruction


    • Scarring of tubule due to inflammation, injury and fibrosis with consequent obstruction


    • Expansion of luminal contents by vectorial fluid/solute shift



      • Electrolyte contents reveal distal or proximal tubular transport function


    • May begin as an ectatic tubule that later becomes a closed cystic space


  • Causes of glomerular cysts unclear



    • May involve scarring of outlet


    • Failure of normal proximal tubule formation



MACROSCOPIC FINDINGS


Differential Diagnostic Features



  • Spherical cysts in bilaterally enlarged kidneys are diagnostic of ADPKD


  • Cylindrical cysts (really ectatic collecting ducts) in enlarged pediatric kidneys are diagnostic of ARPKD


  • A few small cysts at corticomedullary junction are characteristic of NPH


  • Isolated cortical cysts, usually unilateral, are nonhereditary, simple cysts seen in elderly patients with no renal disease


MICROSCOPIC FINDINGS


Differential Diagnostic Features



  • Cysts contain abundant eosinophilic fluid and micropapillary proliferations characteristic of ADPKD


  • Cylindrical cysts are characteristic of ARPKD


  • Glomerular cysts affecting > 5% of glomeruli define glomerulocystic kidney disease as being either primary or secondary


  • Secondary GCKD is more common than primary and presents in children with ADPKD, ARPKD, or TSC



    • Glomerular cysts are defined as Bowman capsule dilation > 3x normal


  • Cysts containing renal cell carcinoma are characteristic of hereditary neoplasia syndromes (TSC, von Hippel-Lindau disease) ADPKD, or hemodialysis-induced cysts


  • Cysts in NPHP/MCDK form are ex vacuo (degenerative); may contain Tamm-Horsfall protein and show tubular basement membrane duplication


  • Incidental, simple cysts are also degenerative and often lack epithelial lining

Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Classification of Cystic Diseases
Premium Wordpress Themes by UFO Themes
%d bloggers like this: