Assymetric hearing loss can be due to many reasons. If the cause is obvious for example after surgery or secondary to trauma or infection in the ear then further investigations other than an audiogram are not neccesary.
When the cause is not known and especially if the hearing loss is sudden and is referred to as a sensori-neural hearing loss then this requires further investigation. Most ENT surgeons would want to perform a MRI of the Internal Auditory Meatus.This is an area in the skull through which the nerves of hearing and balance pass. Occasionally a benign swelling (acoustic neuroma) of one of theses nerves can cause pressure and lead to a assymetric and or sudden sensori-neural hearing loss. The chances of picking one of these up is rare but most surgeons do tend to investigate for this.