Final answer:
The life-threatening complaint that should be reported to the healthcare provider immediately for a client with an acoustic neuroma before an MRI is an intensifying headache.
Step-by-step explanation:
The life-threatening complaint that should be reported to the healthcare provider immediately for a client with an acoustic neuroma before an MRI is an intensifying headache. While the other symptoms (facial numbness, right ear hearing loss, difficulty with balance) are significant, an intensifying headache could indicate increased pressure inside the skull, which could be a medical emergency.