The Bosniak system is used to classify the imaging findings of kidney cysts. (See this webpage for a description of this system, but pl note that it contains medical jargon: http://www.urotoday.com/prod/pdf/reviews/BJU2_may2005.pdf)
Category II are benign cysts with minimal complications. These require follow up with a urologist.
If you need more clarification on this, please ask follow-up questions.
All the best, and God Bless!
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