MCDK is the most common cystic renal lesion in children. A variety of proposed aetiologies have been associated with the underlying pathogenesis of MCDK. These include genetic disturbances, teratogens, in utero infections and urinary tract outflow obstruction (Hains et al. 2009; Lazebnik et al. 1999).

The incidence is 1:4,000 live births and is twice as common in males. The condition is usually unilateral and usually involves the entire kidney. It may be segmental (Jeon et al. 1999) or may involve one pole of a duplex system or one kidney in crossed ectopia (Kiddoo et al. 2005).

Abnormalities of the contralateral kidney are present in approximately one-third of patients (Lazebnik et al. 1999). These include vesicoureteric reflux (18 %) and pelviureteric junction obstruction (12 %) (Atiyeh et al. 1992). Other associated conditions may include ipsilateral genital anomalies and cardiac anomalies.

Nowadays most patients are detected antenatally by ultrasound screening. Foetal MRI may be helpful in difficult cases (Kiddoo et al. 2005) (Fig. 5).

Postnatal imaging is usually by ultrasonography to confirm the diagnosis and to assess the contralateral kidney. It shows a multicystic kidney with cysts of varying sizes which do not communicate, and the intervening renal tissue is echogenic (Fig. 6). Scintigraphy using Tc 99m DMSA shows a non-functioning kidney (Fig. 6). There is no general consensus on the routine use of voiding cystourethrography to determine if there is reflux into the contralateral kidney.

The management of MCDK is usually conservative as its natural history is that of spontaneous atrophy. Follow-up imaging is usually with ultrasonography. Wilms’ tumour has been reported in a patient with MCDK (Oddone et al. 1994), and hypertension has been reported in 23 % patients (Kiyah et al. 2009).

Renal dysplasia is the result of a developmental anomaly characterized by abnormal structural organization and development of metanephric elements. The kidneys may have multiple cysts. It is frequently associated with urinary tract obstruction and is seen in association with posterior urethral valves, prune belly syndrome and pelviureteric junction obstruction. This suggests that obstruction and urinary retention may cause abnormal renal development (Shibata and Nagata 2003).

Antenatal MRI may compliment antenatal ultrasonography in establishing the diagnosis (Fig. 7).

Postnatally on ultrasonography the kidneys are usually normal to small in size with increased cortical echogenicity, loss of corticomedullary differentiation and scattered small cysts (Fig. 8). Voiding cystourethrography may be indicated. Tc 99m MAG3 renography is helpful to confirm if there is associated obstruction to drainage, and Tc 99m DMSA may be required to assess functioning renal tissue.

ARPKD is an inherited disease characterized by nonobstructive fusiform dilatation of the renal collecting ducts resulting in enlarged kidneys. Liver disease is present in all patients with the manifestations varying according to the patient’s age at presentation. The principal pathologic features are periportal fibrosis and biliary duct ectasia. When there is significant liver involvement, it is referred to as congenital hepatic fibrosis (Turkbey et al. 2009). The condition is often referred to as infantile polycystic disease as over 90 % of patients suffer from renal insufficiency during childhood. It occurs in approximately 1:40,000 live births with a gene defect on chromosome 6 (Zerres et al. 1994).

Antenatally there may be oligohydramnios, very large kidneys and absence of bladder filling. MRI may compliment the ultrasound findings (Cassart et al. 2004).

Infants who are severely affected may have pulmonary hypoplasia and Potter’s phenotype and may die from respiratory failure. In selected cases removal of one or both kidneys may improve the respiratory status but the child will usually require dialysis.

Postnatal ultrasonography usually shows enlarged echogenic kidneys with no corticomedullary differentiation. Small cysts up to 3 mm in diameter may be seen and these are usually located peripherally (Boal and Teele 1980). The cysts may be too small to be seen and the echogenic pattern may have a speckled appearance (Fig. 9). As the child gets older, the kidneys may increase further in size and the cysts may enlarge. A family history helps to confirm the diagnosis. Further imaging is only required to follow the condition and this is best performed with sonography. Monitoring of hepatic involvement is necessary to detect complications of portal hypertension. The combined use of conventional and high-resolution ultrasonography with MR cholangiography allows detailed definition of the extent of the kidney and hepatobiliary manifestations without requiring ionizing radiation and contrast agents (Turkbey et al. 2009) (Fig. 9).

ADPKD occurs in approximately 1:1,000 live births. The specific form which develops depends on which of the three genes, PKD1, PKD2 or PKD3, become mutated. In 90 % of patients, the affected gene is located on the short arm of chromosome 16.

The condition may be detected during infancy and childhood either by selective screening where there is a family history or incidentally. It usually presents during adulthood and is often referred to as adult polycystic kidney disease.

The cysts arise from the nephrons and collecting tubules with which they communicate directly, and islands of normal parenchyma are interspersed between the cysts.

Ultrasonography is the imaging modality of choice to investigate these patients. In infants and children, the kidneys may be normal but cysts can be seen in the neonatal period (Fig. 10). The cysts increase in number over time, may become very large and irregularly distributed throughout the kidney and these may compress normally functioning renal tissue. This will be seen as hyperechoic parenchyma on sonography. The cysts may be complicated by secondary haemorrhage, infection or rupture. Complimentary CT or MRI is rarely necessary.

Intracranial aneurysms associated with the condition have been described in neonates and young children (Proesmans et al. 1982). These may be diagnosed using MR angiography.

Medullary cystic disease (MCDC) and NPHP are grouped together as they share many features. NPHP is an autosomal recessive disorder with early onset symptoms, and medullary cystic kidney disease is inherited as an autosomal dominant disorder which usually affects patients in their 30s.

Pathologically they cause cysts restricted to the renal medulla or corticomedullary junction in addition to tubular atrophy, tubular basement membrane disintegration and interstitial fibrosis.

Extrarenal manifestations of NPHP include oculomotor apraxia (Cogan syndrome), retinitis pigmentosa (Senior–Loken syndrome), cone-shaped epiphyses and liver fibrosis (Mainzer–Saldino syndrome), optic nerve coloboma with cerebellar vermis hypoplasia (Joubert syndrome type B) and cranioectodermal dysplasia and electroretinal abnormalities (Sensenbrenner syndrome).