Hello,
I had to Google that one, had never heard of it before.

this is what came up on the search-
http://www.google.com/search?q=pachy...ient=firefox-a
http://www.google.com/search?hl=en&c...ngitis&spell=1

Idiopathic hypertrophic cranial pachymeningitis is a
rare inflammatory disease of unknown origin that affects
the meninges. The diagnosis is made by exclusion
of other known causes of pachymeningitis or thickening
of the dura mater, such as rheumatoid arthritis, sarcoidosis,
syphilis, and tuberculosis. A review of the literature
on idiopathic hypertrophic cranial pachymeningitis reveals
clinical features similar to those in our case (1–6).
The peak age for occurrence is in the sixth decade, and
headaches and progressive cranial nerve palsies are the
most common clinical features.
http://www.ajnr.org/cgi/reprint/19/3/450.pdf