I Am Going Through The Nephrotic Syndrome Disease. . And

I am going through the nephrotic syndrome disease. . And I am taking medicines too... but 1 week ago my doctor asked me about ultra sound and in the result there is a concretion of 2-3 mm size at lower pole... i am confused now... my next appointment is after 1 week but I want to know about this concretion. .. what is this? And how it will effect? What is the cause of it? ...??