This article doesn't go into specifics, so you'll have to find a video of the hearing online somewhere if you want the details. In case you don't feel like searching for it, I'll give a brief summary of the Sonnen situation below.
Chael was diagnosed with Hypogonadism in 2008 and began testosterone replacement therapy to treat this condition.
Chael has notified proper commissions and persons about said treatment since 2008 and has documentation, including CSAC.
Chael's treatment has never come under questioning since 2008.
Chael did not disclose treatment prior to the Silva fight, assuming it was a documented "non-issue."
A third party testing agency was brought in for the Silva fight, who in turn noticed higher than normal levels of a "natural steroid" (whatever the fuck that is) in Sonnen.
The third party agency notified the CSAC about the results, who in turn took action against Sonnen.
The CSAC realized that while Sonnen failed to specify treatment prior to the Silva fight, documentation exists that Sonnen has been diagnosed and treated for hypergonadism since 2008, and has been documented with the proper authorities since 2008.
The CSAC, as usual, fails to admit any mistake on their part, but do elect to shorten Sonnen's suspension to 3 months (in addition to the 3 months already served) and fined him for not submitting the proper documentation (that he'd already submitted multiple times in the past!)
Chael will be back in 3 months. Hopefully fighting the winner of Silva/Belfort.