Have him evaluated by a veterinary neurologist before you make any decisions!
Meningioma's are non-malignant space occupying mass's in the brain that are derived from the tissue that surround the brain, and not the brain itself. The changes in function and behavior that occur are due to the pressure and inflammation that this cancer causes to brain tissue.
Palliative treatment means to treat the symptoms. These include, for example, anti-seizure medications if your dog begins to have seizures, and the use of anti-inflammatories to try to shrink the inflammation in the brain caused by the tumor.
The constraints placed on treatment are generally limited to your funds. An MRI and eventual surgery both require anesthesia, and are costly. The outcome can be very good since this cancer does not metastasize. Radiation is also helpful, but requires multiple treatments, and is also costly.
Consultation with a neurologist is the next logical step. A neurological exam by a neurologist is not too costly, and will answer a lot of your questions.
Thank you doctor. I made an appt. with a neurologist for this coming Tues.