Embryonic Kidney Development

Kidney Development

• Kidneys originate from the mesoderm
• Three temporary renal structures appear during embryonic development in utero
• The first two structures deteriorate
• The third structure eventually develops into the adult kidney

Stages of Kidney Development

• Pronephros forms and deteriorates around week 4
• Mesonephros functions as a temporary kidney during the first trimester
• It contributes to the vas deferens in males
• Metanephros forms the permanent kidney
• It appears around the 5th week
• It develops into the kidney between weeks 32-36

Kidney Formation Structures

• Ureteric bud is an outgrowth of the mesonephric (Wolffian) duct
• It develops into the ureter, renal pelvis, calyces, and collecting ducts
• Metanephric mesenchyme consists of mesoderm tissue
• It is also known as metanephric blastema
• It interacts with the ureteric bud
• This interaction forms the glomerulus to the distal tubule

Kidney Malformation

• Aberrant interaction between the ureteric bud and metanephric mesenchyme can result in kidney malformation

Wilms' Tumor

• It is the most common renal malignancy of young children
• It involves the proliferation of metanephric blastema
• It is associated with embryonic glomerular structures
• It is also associated with mutations of the WT1 gene
• WT1 is expressed in metanephric blastema/mesenchyme

Renal Agenesis

• Renal agenesis occurs when the ureteric bud fails to develop
• Lack of signaling to the mesenchyme is a contributing factor
• In a single kidney situation, the remaining kidney compensates
• It undergoes hypertrophy and hyperfiltration
• This increases the risk of focal segmental glomerulosclerosis (FSGS) and renal failure later in life
• If both kidneys are affected, it leads to oligohydramnios and Potter's syndrome

Multicystic Dysplastic Kidney

• It involves abnormal ureteric bud-mesenchyme interaction
• It is a form of renal dysplasia
• The kidney is replaced with cysts
• There is little or no functioning renal tissue present

Ureteropelvic Junction (UPJ) Obstruction

• UPJ obstruction is the last connection to form
• A common cause is single kidney obstruction
• It involves narrowing at the proximal ureter near the junction
• It can lead to hydronephrosis
• It is often detected during prenatal ultrasound
• Poor urinary flow can cause kidney stones and UTIs
• Surgery can be used to treat it after birth

Duplex Collecting System

• It involves the presence of two ureteric buds on one side
• Or a bifurcation of the ureteric bud
• The upper and lower kidneys form separately
• This can lead to poor urine flow
• Further it can result in hydronephrosis and urinary tract infections
• It is frequently associated with vesicoureteral reflux

Vesicoureteral Reflux

• It is the backward flow of urine from the bladder to the kidneys
• Leads to recurrent urinary tract infections
• Primary reflux results from abnormal closure of the ureterovesical junction (UVJ)
• It occurs in children, and is associated with duplex ureters
• Secondary reflux results from high bladder pressure pushing urine backward
• It is seen with posterior urethral valves

Potter's Syndrome (Sequence)

• The fetus is exposed to absent or decreased amniotic fluid
• Amniotic fluid is composed of fetal urine
• Severe renal malfunction leads to ↓ amniotic fluid
• Loss of fetal cushioning occurs, increasing susceptibility to external forces
• Further it leads to external compression of the fetus
• Abnormalities occur in face/limb formation
• Abnormal lung formation and altered lung liquid movement can occur because of compression

Potter's Syndrome Signs

• Limb deformities
• Flat face
• Pulmonary hypoplasia
• It often leads to fetal death

Oligohydramnios

• Oligohydramnios is rare during the first trimester (1-12 weeks)
• It is linked to decreased formation of fetal urine during the second trimester (13-27 weeks)
• Rupture of membranes in the third trimester (28 weeks to birth) can cause Oligohydramnios

Potter's Syndrome Causes

• Bilateral renal agenesis
  • It is often detected in utero
  • Fetal kidneys can be seen on ultrasound at 10 to 12 weeks
• Posterior urethral valves
  • Occurs in males
  • Tissue obstructs valve outflow
  • Ultrasound shows dilated bladder and kidneys
  • Both kidneys are affected
• Autosomal recessive polycystic kidney disease
  • It is a juvenile form of cystic kidney disease
  • Cysts form in kidneys and the biliary tree
  • Both kidneys are affected
  • Severe cases cause oligohydramnios
  • Less severe cases lead to renal failure and hypertension in childhood

Horseshoe Kidney

• The inferior poles of the kidneys fuse
• The kidneys cannot ascend to the normal position and remain in the retroperitoneum
• They are trapped by the inferior mesenteric artery
• Most patients are asymptomatic
• It is associated with Turner and Down syndrome
• It has also been associated with vesicoureteral reflux

Urachus

• It connects the dome of the bladder to the umbilicus
• It typically obliterates after birth to form the median umbilical ligament.
• Failed or incomplete obliteration can occur
• Urine can leak from the umbilicus, and that may increase the risk of infection
• Cysts, sinuses, diverticulum may also occur

Urachal Remnants

• Urachal remnants can lead to adenocarcinoma of the bladder
• A key feature is cancer at the dome of the bladder
• The classic case involves an adult with painless hematuria
• There might be a tumor at the dome of the bladder
• Pathological examination shows adenocarcinoma