Histology sample. Histology sample showing a typical picture of aneurysmal bone cyst. Hematoxyline-Eosine stain, 20×. Cavernomatous spaces lined with endothelial cells and containing extravasated red blood cells. Note the multinucleated giant cells.Uncommon cause for anterior knee pain - Aggressive aneurysmal bone cyst of the patella. Balke M, Dedy N, Mueller-Huebenthal J, Liem D, Hardes J, Hoeher J - Sports medicine, arthroscopy, rehabilitation, therapy & technology : SMARTT (2010). Not Altered. CC.