Concussion/Brain Injury: cypress, frankincense, sandalwood (brain stem, bottom of feet).
Tumor: Frankincense (brain stem and/or diffuse).
A brain aneurysm can represent mental stress caused by a fear of losing power tied to physical survival, like financial security. Try to work on releasing the fear of money (either having too much or too little).
A brain tumor can represent stubbornness and an inability to change old patterns.