Can mastoiditis lead to spinal meningitis?

Yes: Though quite rare in this day and age, neglected acute mastoiditis can spread into the brain and spinal fluid causing meningitis.

Yes: It's very rare, but infection in the mastoid can lead to infection of the brain covering or meningitis. True mastoiditis is exceedingly rare and often ct scans and MRI scans which show inflammation in the mastoids are incorrectly interpreted as "mastoiditis.".