2. Cystic diseases of the kidney

Question 1

Types of cystic diseases of the kidney

Answer 1

1. Cystic renal dysplasia
2. Polycystic kidney disease (AD, adult form)
3. Polycystic kidney disease (AR, childhood form)

Question 2

Etiologies and associations with cystic renal dysplasia

Answer 2

1. Abnormal metanephric differentiation with persistence of primitive or abnormal structures
2. May be unilateral or bilateral
3. Associations:
   - Ureteric atresia or agenesis
   - Ureteropelvic obstruction

Question 3

Morphology of cystic renal dysplasia

Answer 3

1. Grossly:
   - Usually enlarged kidney, irregular in shape
   - Multicystic
2. Histologically:
   - Lobar disorganisation
   - Multiple cysts of varying sizes lined by flattened epithelium
   - Presence of primitive / immature structures (islands of undifferentiated mesenchymal cells, islands of cartilage tissue, primitive ductal structures)

Question 4

Epidemiology & associations with polycystic kidney disease (AD, adult form)

Answer 4

1. Fairly common (1/400 to 1/1000 live births)
2. Causes 5-10% of cases of chronic renal failure
3. Associated with polycystic liver disease

Question 5

Pathogenesis of polycystic kidney disease (AD, adult form)

Answer 5

1. Mutations in PKD1 & PKD2 genes (encode polycystin-1 & polycystin-2 respectively)
2. Devlopment of multiple cysts that begin as small cysts, gradually enlarging
   - Renal function initially normal
3. Eventually, kidneys are composed almost entirely of cysts, with very little remaining parenchyma (each kidney may weigh up to 4kg)
   - Concordantly, renal function deteriorates over time eventually to end in renal failure
   - This typically occurs in mid to late adulthood

Question 6

Morphology of polycystic kidney disease (AD form)

Answer 6

1. [Grossly]
   - Cysts evident from external surface
   - Cut section reveals multiple cysts containing turbid, red to brown, sometimes hemorrhagic fluid
2. [Histologically]
   - Cysts lined by cuboidal epithelium

Question 7

Epidemiology & associations with polycystic kidney disease (AR, childhood form)

Answer 7

Associated with congenital hepatic fibrosis

Question 8

Pathogenesis of polycystic kidney disease (AR, childhood form)

Answer 8

1. Mutations in PKHD1 gene (encodes fibrocystin)

2. Serious manifestations are usually present at birth & the young infant might rapidly succumb to renal failure

Question 9

Morphology of polycystic kidney disease (AR, childhood form)

Answer 9

1. [Grossly]
   - Smooth external surface
   - Cut section reveals numerous small cysts in the cortex & medulla, giving the kidney a sponge-like appearance
   - Dilated elongated channels are present at right angles to the cortical surface, completely replacing the medulla & cortex
2. [Histologically]
   - Dilation of all collecting tubules
   - Cysts lined by cuboidal cells