There is a photo circulating available on the official WWE website that shows what appears to be a large mass on the back of CM Punk from the company’s Night of Champions pay-per-view on September 15, 2013. You can view it at this link.
To refresh your memory, Punk faced Curtis Axel and Paul Heyman in a 2-on-1 handicap elimination match on the show. Ryback came out and got involved, which obviously resulted in the photo.
In an unprecedented move, WWE challenged Punk’s allegations against their medical staff and mentioned Dr. Chris Amann’s defamation lawsuit against him and Colt Cabana in a public WWE.com post on Friday. Included in their coverage was a 3:40 video of closeup shots of Punk's back that did not show the mass at Royal Rumble on January 26, 2014.
You can watch the video, if you really want to look at Punk’s backside for nearly four minutes, at this link.