Chulalongkorn Medical Journal


Background : The widely-used classification for renal cysts is Bosniak classification whichis also accepted by urologists for diagnoses and management approachesto cystic renal masses. The recent studies show variable incidences ofmalignancy in Bosniak category II, IIF and III lesions. Even in Bosniakcategory II lesion which was previously believed to be benign which had noneed to follow-up has incidence of malignancy.Objective : To detect the incidence of malignancy, time and rates of progression incomplexity of Bosniak category II, IIF and III lesions at King ChulalongkornMemorial Hospital (KCMH).Methods : Searched the term “complex renal cyst”, “Bosniak”, “hemorrhagic cyst” and“complicated cyst” in computed tomographic (CT) and magnetic resonanceimaging (MRI) studies from pictures archiving and communications system(PACS) of our institution from January 1, 2011, to December 31, 2011. Patientswho had Bosniak category II, IIF and III lesions and radiological follow-upincluding CT, MRI and ultrasonography more than 2 years were included inthis study. Re-classification of the cysts was independently performed bytwo blinded readers. Recorded data was sex, age, history or coexistingneoplasm, the number of cysts, characteristic of cysts, duration of follow-up,number of progression in complexity, time to progression and rate ofmalignancy. A total of 109 cases with161 cysts were yielded.Results : A total of 161 cysts were initially reclassified to 144 Bosniak II lesions,15 Bosniak IIF lesions and 2 Bosniak III lesions. Good agreement ofclassification of Bosniak category of these cysts is noted between tworeaders with difference experience. One lesion (6.7%) of resected BosniakIIF was malignant. Four lesions (2.8%) in Bosniak II had progression incomplexity; three lesions were reclassified as Bosniak IIF with time toprogression of 1,626, 1,423 and 477 days and one lesion reclassified asBosniak III with time to progression of 1,904 days.Conclusion : The malignancy rates of Bosniak II, IIF and III lesions in our study are 0%,6.7% and 0%, respectively. This may be underestimated as compared withthose of prior studies due to small sample size.However, imaging surveillanceof Bosniak IIF lesion is stilling recommend due to the chance of malignancyand progression of complexity in a group of Bosniak II lesion which has morecase numbers.


Faculty of Medicine, Chulalongkorn University

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