A photo would be great but what it sounds like to me is that some of the seeds have germinated inside the tomato, which sometimes happens, and they are seen as white threads, if you will.

I wish I'd taken the time to search for a recent thread here where someone found the same thing and posted a picture.

Usually it happens most with soft fleshed varieties such as the gold/red bicolors, as well as lots of times from shipped in grocery store fruits that have been held in storage for quite a while.

Just a suggestion as to what those white threads might be,

Carolyn