Anomalies of number
- Bilateral renal agenesis
- Essentially incompatible with life
- Unilateral renal agenesis
- 1 in 1200
- Often isolated sporadic event – occasionally with other syndromes (Zinner, VATER etc)
- Usually found incidentally
- May not be truly agenesis, but multicystic dysplastic kidney or aplastic kidney – if splenic/hepatic flexure is in normal position, suggests there may have been a kidney which has involuted
- Male 1.8 : 1
- More frequently absent on left side
- Association with Wolffian/mesonephric duct abnormalities, but not really associated with gonadal abnormalities – therefore assumed embryological defect with ureteric bud, rather than metanephros (gonads derived from adjacent mesenchymal tissue to metanephros)
- Up to 50 % males have affected Wolffian/mesonephric duct abnormalities – absent vas, SV, ejaculatory duct)
- Supernumerary
- Truly an accessory organ with its own blood supply, collecting system and parenchyma
Anomalies of ascent
Renal ascent usually occurs between 6 and 9 weeks, rising to its lumbar retroperitoneal location below the adrenal glands.
Incidence of renal ectopia seems to be about 1 in 900.
Associated incomplete rotation means the pelvis is frequently anterior, rather than medial.
Adrenal gland usually normally located.
Higher rates of VUR, hydronephrosis, stones, reproductive tract abnormalities and may be more susceptible to trauma.
More cephalad located ectopia, or even thoracic kidneys (with vessels etc through foramen of Bochdalek) have been described but are usually normally rotated.
Anomalies of form and fusion
Crossed renal ectopia (with or without fusion)
- Rare ? 1 in 7000
- Kidney located on opposite side to ureteric insertion to bladder
- 90 % crossed ectopic kidneys are fused to ipsilateral mate
- Males 2:1
- Left -> right 3:1
- Embryological cause not clear – fusion of the metanephric masses can occur in true pelvis before ascent, or in the latter stages of ascent
- UOs usually orthotopic
Horseshoe kidney
- Common – 1 in 400
- Two distinct renal masses on either side of the midline, connected at lower poles by parenchymatous or fibrous isthmus crossing the midline
- Males 2:1
- Renal pelvises are usually anterior, suggesting fusion occurred before rotation
- Calyces point posteriorly
- Ureter may insert high on renal pelvis
- Horseshoe is usually lower in abdomen, with ascent arrested by the IMA
- Blood supply usually very variable – one artery to each kidney is the exception rather than the rule, and often aberrant supply to the isthmus
- Often associated with other syndromes (Turner, VATER)
- Often appears as hydronephrosis but usually non obstructive on renogram
- PUJ obstruction more common – can be due to extrinsic compression of abnormal vasculature or ureter
- Located above the pelvic inlet – shouldn’t affect pregnancy or delivery
- Postulated to be higher risk of Wilms tumour
- High rates of stones (20 – 60 %) and more risk of trauma
Anomalies of rotation
Normally 90 degree rotation occurs simultaneously with ascent, with the calyces ending pointing laterally (cf posteriorly prior to rotation) and the renal pelvis medially (cf anterior)
Malrotation is often associated with anomalies of ascent or anomalies of form and fusion.
Main issue is impaired drainage and subsequent urinary stasis and stones, and difficulty with endoscopic stone surgery.
Anomalies of renal vasculature
Artery anomalies:
- 70 – 85 % of kidneys have a single artery
- Aberrant vessels (not originating from aorta) are rare except for ectopic or horseshoes
- There are multiple paired renal vessels arising from the aorta during foetal development – as the kidney ascends the lower vessels usually degenerate, leaving a dominant pair
- Most common additional artery supplies lower pole
Renal artery aneurysms and renal AV fistulas are both very rare in the congenital setting.
Anomalies of collecting system
Bifid pelvis – 10 %, considered normal variant.
Calyceal diverticulum
- Cystic cavity within the kidney, lined by transitional epithelium, communicating with a calyx or renal pelvis by a narrow isthmus. Calyceal diverticular do not have papillae.
- Type 1 – adjacent to upper or lower calyx
- Type 2 – larger and communicate with renal pelvis
- Persistence of branches of the ureteric bud which normally degenerate (3rd or 4th generation)
- Often asymptomatic, although up to 40 % of patients may get stones
Hydrocalycosis
- Rare cystic dilation of a major calyx with demonstrable communication to renal pelvis
Megacalycosis
- Non obstructive enlargement of the calyces resulting from malformation of the renal papillae
- Renal pelvis is normal as is PUJ
- Normal function and cortex, thinned medulla
- Male 6:1
Infundibulopelvic stenosis
- Radiologically dysmorphic kidneys – dysgenesis of the pelvicalyceal system but preserved function
- Usually bilateral and associated with VUR