Bridgie thanks for the info. I'll surf that site and learn more. Here is what they had to say.
Immediate post-operative headache may occur in up to 80% of patients after craniotomy but resolves in most patients within 7 days. Fewer than one-quarter develop persistent (>3 months) headache related to the surgical procedure. Posterior fossa procedures, especially suboccipital craniotomies performed for acoustic neuromas, are more likely to be associated with post-craniotomy headache.
The pathogenesis of chronic headache after craniotomy is unclear but may involve meningeal inflammation, nerve entrapment, adhesion of muscle to dura or other mechanisms. Modifications in the operative procedure, including the use of osteoplastic cranioplasty, may lead to a reduction in the incidence of post-craniotomy headache by preventing adhesion of muscle and fascia to the underlying dura.
There is such a laundry list I'm skeptical they can narrow it down. Joe