PEDIATRIC UROLOGY

Risk assessment of incidentally detected complex renal cysts in children: potential role for a modification of the Bosniak classification
Wallis MC, Lorenzo AJ, Farhat WA, Bägli DJ, Khoury AE, Pippi Salle JL
Division of Pediatric Urology, University of Utah, Salt Lake City, Utah, USA
J Urol. 2008; 180: 317-21

• Purpose: Incidentally detected complex renal cysts in children are a rare but worrisome occurrence due to the perceived potential risk of malignancy. We examined the natural history of such cysts in a cohort of children.
• Materials and Methods: We obtained access to a database containing all radiology reports generated at a single institution from 1996 to 2004. We used key words to limit our search, subsequently reviewing charts and images to confirm the diagnosis of a complex renal cyst and to collect clinical data. Cases were categorized according to a modification of the Bosniak classification, using ultrasound in most patients and computerized tomography or magnetic resonance imaging when available.
• Results: Complex renal cysts were identified in 39 children. Mean patient age at presentation was 7 years. Mean cyst size was 1.6 cm. A total of 18 cases diagnosed by ultrasound only were observed with serial imaging. Additional contrast enhanced computerized tomography or magnetic resonance imaging was performed in 21 of 39 patients (54%). Surgical resection was performed in 5 patients and pathological evaluation revealed benign cyst in 3 (modified Bosniak class II in 2 patients and class III in 1) and renal cell carcinoma in 2 (III in 1 and IV in 1). All other patients had modified Bosniak class II cysts, which remained essentially unchanged during a mean follow-up of 26.8 months (range 9 to 70).
• Conclusions: While not validated in children, our data suggest the modified Bosniak classification appears useful as a guideline to direct the management of complex renal cysts in the pediatric population.
  
  
• Editorial Comment
  At Hospital for Sick Children in Toronto, radiology reports from 1996 to 2004 were reviewed looking for renal cysts, including those that were complex and septated. Patients were excluded if they had evidence of cystic kidney disease, prior renal trauma, previous kidney surgery or insufficient data. A minimum of six months follow up was required for inclusion. 39 patients with complex renal cysts were identified with the average age of 7 years and range of 4 months to 14 years, with a mean cystic size of 1.6 cm and a range of 0.4 to 5 cm.
  Initial diagnosis was made in 36 patients by ultrasound and 3 patients were discovered by CT scan. Of the 36 cases discovered by ultrasound half had a CT or MRI scanning, while 18 only had ultrasound follow up. Interestingly in these children 7 simple cysts on CT scan clearly had septations on sonographic imaging, some of which even had Doppler flow in the septations on the ultrasound.
  Five patients had surgical resection and 2 of these patients had renal cell carcinoma in the specimen. All the patients had follow up with a mean of 26.8 months and a range of 9 to 70 months. The cysts were classified according to the adult Bosniak classification.
  Even though these numbers don’t reach statistical significance, the authors recommend for patients with Class II cysts on the Bosniak scale, 3-6 month follow up with ultrasound for the first year and annual ultrasounds thereafter. They did not have a recommendation for how long the annual studies should continue once the cyst has stabilized.
  There is no data in children correlating the predictability of risk factors in the Bosniak classification. However in this study of 39 patients, the worrisome cyst with enhancing margins or septa on CT scan, were the 2 that had renal cell carcinoma found in the specimen. The authors suggest that if there is a concern about an ultrasound cyst, a CT scan should be obtained with contrast to help in classification.
  Bosniak risk classifications are based on renal cell carcinoma incidence in adults. In children, renal cell carcinoma is not the most common tumor and so it’s hard to know how one should think about complex cysts in children. This manuscript suggests that similar concerns of the adult Bosniak classification may very well be worthwhile and that children with cysts certainly should have follow up until the cysts have stabilized, and perhaps for years after that.

Dr. Brent W. Snow
Division of Urology
University of Utah Health Sci Ctr
Salt Lake City, Utah, USA
E-mail: brent.snow@hsc.utah.edu