Definition: The term ?renal dysplasia? defines a developmental anomaly of the kidney resulting from an abnormal differentiation of the metanephric parenchyma (Ridson, 1971).

It represents a collection of anomalies in which kidneys begin to form but then fail to differentiate into normal nephrons and collecting ducts. Dysplasia is the principal cause of childhood end-stage renal failure.

This anomaly of renal differentiation results in a structurally disorganized kidney contain abnormal metanephric elements (primitive ducts and metaplastic cartilage). It consists of microscopic structures not found in normal nephrogenesis.

Two main theories have been considered in its pathogenesis: A primary failure of ureteric bud activity and a disruption produced by fetal urinary flow impairment. Recent studies have documented deregulation of gene expression in human dysplasia, correlating with perturbed cell turnover and maturation.

Mutations of nephrogenesis genes have been defined in multiorgan dysmorphic disorders in which renal dysplasia can feature, including Fraser syndrome, maternal diabetes fetal syndrome, and Kallmann syndrome.

NB: For some authors, renal dysplasia signify only fetal renal cystic diseases.

Epidemiology

 bilateral renal dysplasia: 37% or renal malformations
 unilateral renal dysplasia (with or without controlateral renal agenesis): 7.1% of renal malformations

• segmental renal dysplasia
• focal renal dysplasia

Synopsis

 disorganization of renal architecture

• abnormal tubulogenesis
• abnormal glomerulogenesis
• cyst formation
• immature nephronic (immature nephrons) and ductal structures (immature renal ducts)

 primary ducts or primitive ducts

• small tubules surrounded by concentrically arranged mesenchyme
• tubules are lined by a single layer of cuboidal cells or columnar cells
• thick and eosinophilic basement membrane
• myxoid, moderately cellular condensation of spindle cells around the ductules
• primary ducts derived from the branching collecting ducts. Present in both cortex and medulla, they often become cystic.

 irregularly distributed immature glomeruli and tubules
 connective tissue loose and immature
 islands of immature cartilage (not required)
 renal cysts of varying size, lined by cuboidal or flattened epithelium
 renal cysts involving any part of the nephron
 dilatation of proximal tubules and/or distal tubules
 +/- atretic uretere

Topography

 focal renal dysplasia
 segmental renal dysplasia
 diffuse renal dysplasia

• unilateral diffuse renal dysplasia
• bilateral diffuse renal dysplasia

Etiology

 obstructive renal dysplasia (obstructive multicystic renal dysplasia) (urinary tract obstruction at any level)

• segmental obstructive renal dysplasia
• bilateral obstructive renal dysplasia

 multicystic renal dysplasia (diffuse cystic renal dysplasia)

• nonsyndromal diffuse cystic renal dysplasia
  • hereditary renal adysplasia (association of a renal dysplasia and unilateral renal agenesis)

• syndromal diffuse cystic renal dysplasia
  • inherited metabolic diseases
    • Zellweger syndrome (MIM.214100)
    • carnitine palmitoyltransferase deficiency (MIM.255110)
    • glutaric aciduria type 2 (MIM.231680)
    • Smith-Lemli-Opitz syndrome

 solid non-cystic renal dysplasia

Miscellaneous associations

(NB: renal-hepatic-pancreatic dysplasia (former Ivemark II syndrome) has not been considered as a renal dysplasia and is referred in ARPHD (autosomal recessive polycystic kidney disease).

Variants

 renal adysplasia (association unilateral renal agenesis and controlateral renal dysplasia)
 hypoplastic renal dysplasia (small kidneys with extensive renal dysplasia)
 aplastic renal dysplasia (association of a renal dysplasia and unilateral renal agenesis)

Differential diagnosis

 renal polycystic diseases (renal PKDs)

Animal models

 cyclooxygenase-2 null mice (COX2-null mice) (11115063)

Case records

 Case 11385: Renal adysplasia (association unilateral renal agenesis and controlateral renal dysplasia)
 Case 12763: Non-syndromic bilateral non-obstructive multicystic renal dysplasia (non-syndromic BNOMRD)

References

 Jain S, Suarez AA, McGuire J, Liapis H. Expression profiles of congenital renal dysplasia reveal new insights into renal development and disease. Pediatr Nephrol. 2007 Jul;22(7):962-74. PMID: 17450386

 Bisceglia M, Galliani CA, Senger C, Stallone C, Sessa A. Renal cystic diseases: a review. Adv Anat Pathol. 2006 Jan;13(1):26-56. PMID: 16462154

 Woolf AS, Price KL, Scambler PJ, Winyard PJ. Evolving concepts in human renal dysplasia. J Am Soc Nephrol. 2004 Apr;15(4):998-1007. PMID: 15034102

 Shibata S, Nagata M. Pathogenesis of human renal dysplasia: an alternative scenario to the major theories. Pediatr Int. 2003 Oct;45(5):605-9. PMID: 14521545