Nephrogenic Rests



Nephrogenic Rests


Satish K. Tickoo, MD

Victor E. Reuter, MD





Key Facts


Terminology



  • Abnormally persistent nephrogenic cells, capable of developing into nephroblastomas


Clinical Issues



  • Encountered in up to 40% of patients with Wilms tumor and > 95% in patients with bilateral tumors


  • Both PLNR and ILNR are observed in patients in Western countries, but PLNR are rarely, if ever, seen in Asian countries


Microscopic Pathology



  • PLNR usually multifocal, located at periphery of renal lobes and sharply demarcated from surrounding renal parenchyma


  • ILNR usually unifocal, localized within renal lobes, and poorly circumscribed with interdigitations into surrounding nephrons


  • Dormant NR, small rests without evidence of proliferation


  • Sclerosing and obsolete rests consist predominantly of tubules in fibrotic background


  • Hyperplastic NR, showing signs of proliferation with abundant blastemal elements and increased size


  • Neoplastic NR, arising within dormant, sclerosing, or hyperplastic rests


  • Presence of pseudocapsule important in distinguishing hyperplastic or neoplastic (adenomatous) rest from nephroblastoma


Top Differential Diagnoses



  • Papillary adenoma







Perilobar nephrogenic rests are located at the periphery of the renal lobes, well delineated from adjacent nephrons, and composed of blastema and tubules without any significant stromal components.






Interlobar cell rest is adjacent to a Wilms tumor image. ILNRs image are located within the renal lobes, have irregular outlines, and often show prominent stromal components.


TERMINOLOGY


Abbreviations



  • Nephrogenic rest (NR), perilobar nephrogenic rest (PLNR), intralobar nephrogenic rest (ILNR)


Definitions



  • Abnormally persistent nephrogenic cells associated with and capable of developing into nephroblastomas


ETIOLOGY/PATHOGENESIS


Molecular Alterations



  • Like those in Wilms tumor (WT), alterations in WT1 (11p13), WT2 (11p15), and WT3 (16q) genes are present in accompanying NRs



    • Mutations in WT1 are present in ILNR


    • Insulin growth factor 2 loss of paternal imprinting (LOI) (in putative WT2 gene region) in PLNR of all types (sclerosing, hyperplastic, etc.)


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Encountered in up to 40% of patients with WT; incidence > 95% in patients with bilateral tumors


    • Observed in 1% of infant autopsies; isolated intralobar NRs less common (1 in 1,000 autopsies)


  • Age



    • Median at presentation: WT and ILNR = 18.5 months; WT and PLNR = 35.5 months


  • Gender



    • WT and NR show equal sex distribution or slight female preponderance in the West, but significant male preponderance in Asia


  • Ethnicity



    • PLNR somewhat more common than ILNR in West, but PLNR extremely uncommon in Asia


Treatment



  • Hyperplastic rests difficult to distinguish from WT on biopsy; these and later forms treated similar to stage 1 WT (National Wilms Tumor Study Group [NWTS])



    • Treating hyperplastic rests prevents compression and damage to native kidney


    • Also, treating these diminishes targets for neoplastic transformation


Prognosis



  • NRs in WT-bearing kidneys are associated with higher incidence of synchronous or metachronous WT in other kidney



    • Higher incidence of concurrent bilateral Wilms tumor in patients with NRs, particularly PLNR


    • Risk of metachronous WT 15x higher in children < 1 year of age with WT and NR (particularly PLNR) than those without NR


    • Identifying NR on nephrectomy for WT leads to increased frequency of ultrasonographic follow-up for child

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Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Nephrogenic Rests

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