Autosomal recessive polycystic kidney disease (ARPKD)
1 in 10 000 – 40 000
Mutation of polycystic kidney and hepatic disease 1 gene (PKHD1) – produces the protein fibrocystin.
Often diagnosed antenatally or in infancy.
- Antenatal USS – diffuse bilateral renal enlargement, with oligohydramnios/small bladder.
- Infancy – hypertension, palpable masses, pulmonary hypoplasia.
Up to half of cases lethal within first few weeks of life – oligohydramnios of pregnancy leading to pulmonary hypoplasia.
Renal parenchyma is replaced by innumerable cysts, usually 2 mm or less in diameter – inevitable progression to renal failure.
Liver is also invariably involved, with congenital hepatic fibrosis.
Prognosis for those surviving the neonatal period / escaping pulmonary complications – 87 % 5 year survival and 67 % 15 year survival – but often needing transplant as well as treatment for hepatic complications.
Consider genetic screening/counselling – autosomal recessive, so 1 in 4 chance of siblings being affected.
Autosomal dominant polycystic kidney disease (ADPKD)
Much more common – 1 in 400 to 1 in 1000 – but usually presents in adulthood in 40s and 50s.
Multiple expanding cysts of both kidneys which ultimately destroy renal parenchyma causing renal failure.
85 % of cases affecting PKD1, 15 % of cases affecting PKD2.
Associated with hypertension, hepatic cysts, Berry aneurysms, diverticulosis, mitral valve prolapse and other cysts (pancreas, spleen, SVs)
Multicystic dysplastic kidney (MCDK)
Developmental anomaly resulting in multiple cysts of varying sizes without identifiable normal renal parenchyma and subsequently no function. Usually the contra-lateral kidney is normal and may be hypertrophied.
Unilateral MCDK incidence around 1 in 2500 – 1 in 4000.
Bilateral MCDK is lethal.
Thought to be due to complete ureteric obstruction during embryological development – usually proximal ureteric atresia. Rarely may be due to distal obstruction such as ureterocele. An alternate theory is abnormal interaction between the ureteric bud and the metanephric mesenchyme.
Usually sporadic with no role for familial screening.
Pathology:
- Irregular collection of tense non-communicated cysts lined by cuboidal or flattened tubular epithelium
- “bunch of grapes”
- Usually little renal parenchyma – small islands or flattened planes of dysplastic tissue interposed between cysts
Presentation:
- Usually found on antenatal imaging
- Ultrasound repeated after birth – confirm diagnosis and check contra-lateral kidney
- Occasionally with present as large abdominal mass
Differentiating from severe hydronephrosis:
- MCDK – haphazard distribution of cysts of varying sizes great and small, without a larger central or medial cyst
- PUJO or hydronephrosis – cysts (calyces) organised around periphery of kidney, which can often be demonstrated to join central cyst (renal pelvis); absence of smaller cysts
- Renogram can be helpful – MCDK will show no function while hydronephrotic kidneys will show some
20 – 30 % will have contralateral reflux – usually low grade – role of MCUG controversial – probably only need ultrasound surveillance + MCUG if febrile UTIs.
Up to 10 % may have contralateral PUJ obstruction.
A large proportion will involute in early years of life and hence may be confused for renal agenesis.
The risk of malignancy and hypertension have been cited as reasons for prophylactic nephrectomy of MCDK in the past – generally now observation or no treatment preferred. Hypertension seems rare. Large symptomatic masses are treated with nephrectomy.
Multilocular renal cyst (cystic nephroma)
- Sporadic / not inherited
- Unclear if neoplasm or developmental abnormality – but thought to be on a spectrum with benign cystic nephroma at one end, cystic Wilms tumour at the other
- Rare
- Often incidental or may present with haematuria / flank pain
- Multilocular cystic neoplasm usually localised within parenchyma – may be difficult to distinguish from Wilms tumour
- Benign but because cannot be distinguished from Wilms -> usually surgically excised with nephrectomy
Simple renal cyst
- Rare in children
- Differential is a cystic dilation of a non-functioning upper moiety
- Management and presentation similar to adults – usually incidental – occasionally symptomatic and worth treating if large
What are the differentials for an ultrasound showing multiple cysts in a child?
- Hydronephrosis
- Multicystic dysplastic kidney
- Polycystic kidney disease (usually autosomal recessive in children)
- Cystic nephroma / multilocular renal cyst
- Cystic Wilms tumour
- Dilated unit of a duplex / upper pole
- Simple renal cysts
- Parapelvic cysts