Christina Norman, president of MTV since 2005 and an MTVN vet of 17 years, is leaving the Viacom unit at the end of the month. Van Toffler, president of MTV Music and Logo Group, made the announcement in an internal memo late this afternoon. Toffler, who headed the network before, will take on the day-today operations indefinitely while maintaining his group role.

The mantra from HQ is this is her decision and there’s no reason not to believe it. Toffler: “It pains me to see Christina go, but I respect her decision to want to take the time to explore something new after 17 years, which is pretty much impossible to even think about while running the M. ... Christina made it clear that MTV’s current creative vibrancy and thriving business provided her with the perfect timing to explore something new. MTV has several TV hits cranking, the fastest selling video game with Rock Band and a rapidly growing collection of websites. We’re positioned as an industry leader with an array of verticals and Emmy Award-winning virtual worlds, and we’re shaking up the 2008 elections with “Street Team ‘08.”

Norman is the latest—and the highest ranking—MTVN exec leaving to look for something new. Michael Hirschorn left VH1 with
Stella Stolper to set up a production house but have first-look deals with MTVN (NYSE: VIA). Could Norman wind up with something that maintains her ties?