There's probably some legalese or case precedent somewhere addressing particular rights, tissue/slide ownership, and all that. That notwithstanding, in practice a pathologist does have to "approve" the request, and the surg path department certainly has to know about it in order to get the material ready and ship it out. But I can't recall a pathologist/group in a hospital setting which wasn't willing to let recuts go out to someone else by clinician request -- so long as who was paying for what was sorted out first. Occasionally there can be problems if there is extremely limited tissue of interest, or an outside consultant insists on seeing the actual original slides/tissue; this can come up in cases undergoing litigation, where the original institution doesn't want to release custody of the primary material and the consultant doesn't want to physically go to the original institution to do their evaluation. Pathologists can be viewed as consultants, but in the context you're talking about the original pathologist also has the primary responsibility of issuing a tissue diagnosis -- tissue is literally signed over to them by requisitions and these patients are also their patients, at least as much as that of the cardiologist and nephrologist and oncologist and surgeon and so on.
But in common practice, asking for a 2nd path opinion is unlikely to be stonewalled unless there is a "who-is-paying-for-what" issue going on, it's happening absurdly often, or some such. That doesn't mean they aren't going to want an explanation or that they won't feel a bit slighted -- pathologists already will send out for a consult if it's thought to be indicated, and most people have a little professional pride, such that they want their clinicians to have confidence in them. While it's common for a patient to go for a second clinical opinion and that second institution to request recuts or whatever for their local pathologists, almost always explained in a request letter if not by phone, it could be considered a little rude & unprofessional to ask them to send out for a second path opinion without any explanatory communication at all. Talk to them about what you want and why, how confident they feel with the diagnosis, etc., and see if you can agree on a course of action.
