Wish I had a categoric answer to this: unfortunately I don't ... and I frequently have the same problem. Currently, there are FOURTEEN instances of SVCHOST running on my PC, which is quite normal (for me), all without problem.
Occasionally, one goes haywire, like yours. I've never fully pinned down what causes this, so hopefully someone a bit smarter will be along shortly to enlighten us?
Meanwhile, 2 observations: I've often noticed that this MAY be linked to an AV software malfunction (I'm using Vipre, which works very well apart from an occasional 'hang'). Second, all I normally do is right-click within Task Manager on the offending instance of SVCHOST, and terminate the process.
So far, it solves the immediate problem of high CPU usage without impacting on anything else, but I'll re-iterate, I have no real idea what is the cause