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

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.

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
 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