Cystic nephropathies Q61.9

Already around 460 B.C. Hippocrates described for the first time a probably polycystic kidney disease. The first comprehensive description is found in 1829 - 1835 by Cruveillhier. In 1899 Steiner pointed out the hereditary nature of cystic nephropathies. In 1934 Marquardt differentiated between two different modes of inheritance and in 1957 a comprehensive monograph on clinic and genetics by Dalgaard was published. In 1971, Blyth and Ockenden comprehensively described the clinical variability of the autosomal recessive and autosomal dominant forms. Just 1 year later, they were able to localize 4 different gene loci for ARPKD. In 1985, the gene was first mapped by Reeders et al. and cloned in 1994 (Ganten 2013). Laurence and Mond reported in 1866 a family with typical symptoms of a Bardet- Biedl- syndrome. Bardet and Biedl independently described in detail the BBS named after them in 1995 (Forsythe 2013).

The cystic nephropathies belong to the generic term of hereditary nephropathies, along with glomerular diseases, metabolic hereditary nephropathy, phakomatoses and disorders of tubular renal function (Herold 2021). The cystic nephropathies consist of etiopathogenetically different rare hereditary and non-hereditary malformation syndromes as well as dysplastic kidney diseases with cyst formation.

The cystic nephropathies are subdivided into:

Dysplastic kidney disease with variable cyst formation

• Multicystic dysplastic kidney disease (MCDK): MCDK is a severe developmental disorder in which the kidney tissue consists increasingly of cysts and often lacks a pelvicocaliceal system. There is no relevant organ function (Manski 2019). Associations with syndromes or chromosomal aberrations are sometimes found. MCDK corresponds to the historical classification "Potter II- dysplasia" (Sohn 2013).
• Renal dysplasia with cysts: This is a restricted functional parenchyma, which can occur unilaterally or bilaterally. Smaller cysts are often found. Renal dysplasia can occur in isolation or as part of various syndromes. (Gimpel 2019)
• Simple renal cysts: These can occur unilaterally or bilaterally, solitary or multiple and are often diagnosed as incidental findings (Herold 2021). They are usually located in the cortical region of the kidney and are filled with a homogeneous fluid (Keller 2010). For more details see. Renal cysts

Cystic kidney diseases with classical inheritance

• Autosomal dominant polycystic nephropathy (ADPKD) s. d.
• Autosomal recessive polycystic nephropathy (ARPKD) s. d.
• Nephronophthisis: It comprises a group of tubulo-institutional nephropathies (Herold 2021). For more details, see. Nephronophthisis
• Alström syndrome (syn. Alström- Hallgren syndrome): This is a rare multisystem disease (Schmidt 2006) that belongs to the group of ciliopathies.
• Autosomal dominant tubulointerstitial kidney disease (ADTKD): It represents the largest heterogeneous group of hereditary diseases that occur only in adulthood (Knaup 2019). For more details see ADTKD
• Medullary sponge kidney: Medullary sponge kidney is a congenital malformation of the kidneys with: malformation of the terminal collecting tubes in the medullary pyramids and papillae, formation of medullary cells.

Polycystic kidney disease with syndromic appearance

• Laurence-Moon-Bardet-Biedl syndrome (BBS): Rare malformation syndrome belonging to the ciliopathies

  (mental retardation, retinopathy, obesity, polydactyly, malformations of the kidneys)

• Meckel- Gruber- syndrome (MGS): malformation complex also known as dysencephalia splanchnocystica (Entezami 2002).
• Jeune syndrome: malformation complex also known as "asphyxiating thoracic dysplasia".

Sonographically should be documented in all cysts in childhood:

• renal size
• uni- or bilateral changes
• number and localization of cysts
• possible indications of renal dysplasia like e.g. cortical echogenicity, mar- cortical differentiation
• presence of any malformations of the urinary tract (Kemper 2020).

In all genetic cystic kidney diseases, an extrarenal manifestation should also be sought in any case (Herold 2021).

Cystic space lesions are classified according to Bosniak for morphological evaluation and subsequent treatment planning (Lerchbaumer 2018) into:

• Bosniak I: The cyst is clearly benign. There is no risk of malignancy.
• Bosniak II: The cyst is < 3 cm in size. There is mild septation, hyperdense lesions without contrast uptake, and thin calcifications. There is no risk of malignancy, and controls are not required.
• Bosniak IIF: These cysts are not clearly classified as group II or III. There is a 5% risk of malignancy. The F stands for "follow up": regular controls are required.
• Bosniak III: There are septa > 1 mm thick. The cyst wall shows irregular thickening with contrast enhancement. Primary indistinct densities are seen on CT. The cyst is not clearly benign, the risk of malignancy is 50%. Further diagnostic workup is absolutely necessary.
• Bosniak IV: The cyst appears suspicious for malignancy: It is sonographically not primarily recognizable as a cyst, shows a protruding solid process and / or a centrally disintegrating tumor. The risk of malignancy is 75 % - 90 %. Further diagnosis or surgical measures are urgently indicated (Manski 2019 / Kuhlmann 2015 / Bartels 2013).

Widely used is the AAP- classification of the American Academy of Pediatrics (AAP), which divides cystic kidney disease as follows:

• 1. genetically caused cystic kidney diseases (so-called hereditary nephropathies):
  • autosomalrecessive polycystic kidney disease (ARPKD)
  • autosomal dominant polycystic kidney disease (ADPKD)
  • juvenile nephronophthisis
  • medullary cystic disease
  • congenital nephrosis syndrome
  • familial hypoplastic glomerulocystic kidney disease
  • malformation syndromes such as von Hippel-Lindau syndrome, tuberous cerebral sclerosis, etc.
• 2. non-genetic cystic kidney diseases:
  • simple renal cyst
  • parapelvic renal cyst
  • Acquired cystic kidney disease
  • Calyx diverticulum
  • benign multilocular renal cyst
  • medullary sponge kidney (see above)
  • multicystic kidney dysplasia (MCDK) see above (Manski 2019)

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