Whats using the space in my TEMPDB?

Platform is SQL 2008 R2 SP1.

How is this possible?

• sys.dm_db_file_space_usage shows user_object_reserved_page_count of approx 4.4g
• sys.dm_session_space_usage shows 0's in every column for every session

What is using the 4.4g in my TEMPDB?

Chuck