Complex kidney cysts (an ultrasound video study):

                                                                          

Case-1:Sagittal section ultrasound video clip showing the complex nature of the right renal cyst. This cyst is small and septate (fine septations). Note the presence of small calcifications in the lower part of the cyst.
Same case as above- another ultrasound video clip:

                                                                            

This cyst was seen in a middle aged male patient and was an incidental finding. CT scan reports suggest this is a Bosniak category 2 complex renal cyst. Indeed the ultrasound findings did not change over a period of time, nor did the cyst increase in size. This complex renal cyst measures 1.7 cms. in size.                                          
Case-2:

                                                                        The above ultrasound video clip shows a larger complex cyst in the left kidney of an elderly male patient. Again, the cyst might fit in with a Bosniak category-2 complex renal cyst. This renal cyst shows fine (but thicker than those in case-1 above) membranous partitions and a few calcifications along the cyst wall.                                                                                          
                                                                       This 2nd renal ultrasound video clip shows that there is a 2nd smaller cyst adjacent to the larger cyst. This one also shows few calcific lesions along the wall. These appearances suggest a benign nature of these complex cysts of the left kidney.                                                                                                                                   

                                                                          

 The above color Doppler video clip of the left kidney (same case-2) shows no significant vessels along the walls of the cysts or in the septae within them, again confirming the benign nature of these lesions.                    Read more at: http://www.kidneycancerinstitute.com/kidney-cyst.html
Also view ultrasound images of renal cysts and cystic diseases of kidneys at:
  http://www.ultrasound-images.com/kidneys.htm