A committee of international experts in pediatric nephrology, pediatric radiology, pediatric US, and adult nephrology prepared systematic literature reviews and formulated recommendations for Imaging of Kidney Cysts and Cystic Kidney Diseases in Children. The purpose of this consensus statement is to provide clinical guidance on standardization of imaging tests to evaluate kidney cysts in children. The final statement was endorsed by the European Society of Pediatric Radiology, the European Federation of Societies for Ultrasound in Medicine and Biology, the European Society of Pediatric Nephrology, and reviewed by the European Reference Network for Rare Kidney Diseases. The consensus statement has appeared in the Journal Radiology.
Kidney cysts can manifest as a focal disease (simple and complex kidney cysts), affect a whole kidney (eg, multicystic dysplastic kidney or cystic dysplasia), or manifest as a bilateral cystic disease (eg, autosomal recessive polycystic kidney disease [ARPKD] or autosomal dominant polycystic kidney disease [ADPKD]). In children, as opposed to adults, a larger proportion of kidney cysts are due to genetic diseases (eg, HNF1Bnephropathy, various ciliopathies, and tuberous sclerosis complex), and fewer patients have simple cysts or acquired cystic kidney disease.
The International Expert group has a final consensus on the following statements-
- Ultrasound is the method of choice when assessing pediatric kidney cysts, with selected indications for MRI and the contrast-enhanced US. CT should be avoided whenever possible because of ionizing radiation.
- Renal Ultrasound yields essential diagnostic information in many cases. In patients with ARPKD or other ciliopathies, abdominal US is needed for diagnosis and screening of portal hypertension.
- The US is usually sufficient for follow-up kidney imaging, but MRI can be valuable for clinical trials in patients with ADPKD or in older children with tuberous sclerosis complex to evaluate both kidney cysts and angiomyolipomas.
Following are the major recommendations:
Technical Issues and General Recommendations
- Kidney cysts and cystic kidneys should be investigated by using the Ultrasound in the first instance, with detailed examination and description of the renal parenchyma, urinary tract, and cysts.
- US examination of the liver is recommended for initial evaluation of cystic kidney disease. Additionally, transabdominal genital system US should be performed in female patients at first examination.
- US should be performed by an experienced examiner, with special training in pediatric US using the highest possible resolution transducers with settings optimized to the child.
- There are insufficient data in children for the use of contrast-enhanced US in cystic kidney disease.
- MRI is not routinely necessary and should be restricted to selected cases of pediatric kidney cysts. Examination techniques should be customized to the pediatric patient.
- CT should not be routinely used for investigation of pediatric kidney cysts because US and MRI usually provide better contrast resolution without radiation exposure. It may be useful in a very small subset of children (eg, those with claustrophobia or when MRI is not available even with referral). Examination techniques should be customized to the pediatric patient.
- Cystic kidney diseases often manifest only with hyperechogenicity and/or enlarged kidneys prenatally. Oligohydramnios and extrarenal features, such as congenital malformations and reduced lung volume, are important imaging findings because they affect prognosis. Regular monitoring and multidisciplinary care are required during pregnancy and postnatally.
- By definition, a simple cyst occurs in a kidney with otherwise normal parenchyma and a normal contralateral kidney. It is round, thin-walled, anechoic, nonseptated, separate from the collecting system, and has no Doppler blood flow related to the cyst.
- A child with a first-time diagnosis of a single kidney cyst requires a detailed medical and family history, thorough clinical examination, and at least one follow-up assessment.
- A simple cyst in a child does not need contrast-enhanced US, MRI, or CT imaging.
- An MCDK is characterized by replacement of the whole kidney with multiple disorganized cysts lacking any normal surrounding parenchyma. If functional renal imaging is performed, no (or minimal) function is seen.
- In children with unilateral MCDK, renal functional imaging, such as dimercaptosuccinic acid (DMSA) or technetium 99m diethylenetriamine pentaacetate (DTPA) scintigraphy is not recommended, particularly if the contralateral kidney is structurally normal at US with compensatory hypertrophy.
- In children with unilateral cystic dysplasia or MCDK, the contralateral kidney should be monitored with the serial US to ensure continued appropriate compensatory hypertrophy.
- Children with bilateral cystic dysplasia or unilateral cystic dysplasia/MCDK without contralateral compensatory hypertrophy are at increased risk for progressive chronic kidney disease and require follow-up by a pediatric nephrologist.
- There is no evidence for an increased risk of malignancy in MCDK in children and young adults; therefore, monitoring solely to exclude malignancy is unnecessary.
- Cystic dysplasia is characterized by at least one cyst within an abnormal kidney (eg, hyperechogenic parenchyma, loss of corticomedullary differentiation, small kidney).
- Dilated calyces in patients with high-grade obstruction or a urinoma may be misdiagnosed as kidney cysts. If there is any suspicion of urinary flow impairment, a further urologic examination is recommended.
- The diagnosis of HNF1B-associated disease cannot be made with kidney imaging alone and requires genetic confirmation.
- Girls with HNF1B mutations should be examined with the transabdominal US of the genital tract.
- Since US findings of nephronophthisis are nonspecific, the diagnosis cannot be based on imaging findings alone. In addition, MRI of the kidneys does not help diagnosis or management.
- Children suspected of having nephronophthisis should undergo the abdominal US to look for signs of liver fibrosis and portal hypertension.
- In children suspected of having nephronophthisis and disability, developmental delay, or cerebral dysfunction, cranial MRI is suggested to look for cerebellar vermis hypoplasia.
- Since imaging findings are nonspecific, the diagnosis of Bardet-Biedl syndrome cannot be made on the basis of imaging findings alone.
- Regular kidney imaging is not required in children with nephronophthisis. However, monitoring for signs of hepatic fibrosis is recommended in children with genetic defects known to be associated with liver involvement and those with an unknown genotype. Monitoring in children with Bardet-Biedl syndrome and HNF1B-associated disease will depend on the type of renal and urinary tract involvement.
- The classic US appearance of ARPKD is bilaterally enlarged kidneys with heterogeneous parenchymal echogenicity with a salt-and-pepper pattern. This imaging appearance is caused by multiple tiny cysts smaller than or just approaching the size necessary for detection, which disrupts the echo pattern without being clearly distinguishable. However, the renal sonographic phenotype can be variable: kidney size may range from normal to massively enlarged, hyperechogenicity can be limited by the medulla or diffuse, and cysts can appear as ductal dilatation or as macrocysts of variable size, number, and location.
- In children with known ARPKD, annual abdominal US is suggested to monitor for signs of portal hypertension. In severely affected infants with progressive disease, kidney size should be monitored according to clinical needs.
- ADPKD is characterized by the gradual development of multiple cortical and medullary cysts from early life. Initial presentation may be antenatal with subtle cortical hyperechogenicity and renal enlargement. Overt cyst development may then be detectable at any stage from before birth through childhood. The Pei Ravine criteria for US diagnosis of ADPKD (three or more uni- or bilateral cysts) were derived from patients older than 15 years and have low sensitivity in younger children. In patients younger than 15 years with a positive family history, the presence of at least one kidney cyst, kidney enlargement above normal limits, or both should be considered highly suggestive of ADPKD.
- There are important ethical controversies and psychosocial issues surrounding the use of presymptomatic imaging to diagnose ADPKD in minors, as therapeutic consequences may not arise until adulthood.
- In children suspected of having ADPKD without a genetic diagnosis or a clear family history, confirmatory US should be performed within 12 months after the initial screening. In children with multiple cysts, enlarged (2 or more standard deviations larger than the mean) kidneys, or both, serial renal US may be helpful but should not be performed more frequently than once per year unless patients have complications (eg, pain or hematuria). MRI should be restricted to rare cases when further imaging is needed and the US is not feasible.
- In pediatric clinical trials in patients with ADPKD, total kidney volume determined with MRI is recommended to monitor progression in cooperative children.
- US monitoring of kidney size and cyst number is preferable to MRI in uncooperative children with ADPKD.
- The diagnosis of TSC is based on diagnostic criteria, including clinical characteristics and imaging findings (mainly on cerebral MRI). Kidney involvement in TSC can include AML or kidney cysts, which may be detected by using kidney US or MRI.
- For observation of children with known TSC (classic and CGS), renal US is suggested until puberty, and MRI is recommended thereafter.
- Typical signs of malignancy at US are a unilateral single cystic mass with a thickened wall, septations, and possibly calcifications or enhanced perfusion at colour Doppler imaging.
- US should be used in the initial assessment of complex cysts, with further imaging performed with contrast-enhanced MRI in cases of suspected malignancy. The contrast-enhanced US may be performed in experienced centres for further evaluation.
- ACKD is characterized by multiple small cysts, usually occurring bilaterally in small kidneys, predominantly in the setting of end-stage renal disease, or in native kidneys after kidney or liver transplantation.
- In patients on renal replacement therapy and after renal transplantation, yearly US follow-up of native kidneys is suggested to monitor for ACKD.
For more details click on the link: https://doi.org/10.1148/radiol.2018181243
Author Dr.Kartikeya Kohli DNB (Medicine), MRCP, Fellow DNB(Nephrology) is a Consultant Physician and Nephrologist at Sanjeevan Hospital, New Delhi