I don't know about sinuses, but an MRI (WITH contrast) can rule out the possibility of an acoustic neuroma, a benign tumor of the inner ear (hearing nerve).
Acoustic neuromas usually cause gradual or (more rarely) sudden one-sided hearing loss and/or ringing in the ear, and can also cause vertigo or dizziness, although I think only about 5 or 3 percent of cases of unilateral hearing loss turn out to be acoustic neuroma, and dizziness/vertigo have many, many, MUCH more common causes than acoustic neuroma.
The MRI will likely not show anything--headaches and vertigo have many causes, most of which are not due to tumors or anything scary like that.
With headaches and vertigo, one possibility could be "migraine-associated vertigo." Check it out.
The Content on this Site is presented in a summary fashion, and is intended to be used for educational and entertainment purposes only. It is not intended to be and should not be interpreted as medical advice or a diagnosis of any health or fitness problem, condition or disease; or a recommendation for a specific test, doctor, care provider, procedure, treatment plan, product, or course of action. MedHelp is not a medical or healthcare provider and your use of this Site does not create a doctor / patient relationship. We disclaim all responsibility for the professional qualifications and licensing of, and services provided by, any physician or other health providers posting on or otherwise referred to on this Site and/or any Third Party Site. Never disregard the medical advice of your physician or health professional, or delay in seeking such advice, because of something you read on this Site. We offer this Site AS IS and without any warranties. By using this Site you agree to the following Terms and Conditions. If you think you may have a medical emergency, call your physician or 911 immediately.