A couple of months ago, I did a post regarding the use of ABR (Auditory Brainstem Response) testing as part of a comprehensive vestibular evaluation. I revisit the topic to discuss the relevance of abnormal findings associated with that test. While ABR testing has other benefits, the primary purpose of the test in the vestibular lab is to determine if there is any asymmetry in neural response between the two auditory/vestibular nerves (otherwise known as cranial nerve VIII). One cause of such asymmetry could be a small tumor known both as a vestibular schwannoma (VS) or an acoustic neuroma (AN). These are small encapsulated tumors that do not spread throughout the brain or to other parts of the body. The problems is that they take up space, and there isn’t much extra space in the Cerebello-Pontine Angle (CPA) which is the pathway of the nerve from the labyrinth, through the skull, to the brain.
When a VS or AN is detected in the CPA, the concern is that it might grow and put pressure on the auditory/vestibular nerve or facial nerve which follows a similar pathway. Potential symptoms associated with VS or AN are decreased hearing, tinnitus, dysequilbrium, headache, and facial nerve weakness.
Of course, if the ABR test is abnormal an MRI scan would be needed to confirm any suspicion of VS or AN. These tumors affecting balance are rare and we find just a few a year in a busy vestibular clinic. The patients are understandably concerned about what happens next if a tumor is found.
Two recent studies looked into the long term affects of different treatment approaches on health related quality of life and symptoms of ongoing dizziness. The group studied all had small VS and underwent one of three treatments. Some underwent surgery to remove the tumor, some received stereotactic radiotherapy (a form of focused radiation therapy), and others were simply observed over time to monitor growth in tumor size and increase in symptoms.
On several measures related to quality of life (Q of L), there was no difference between the three treatment groups. Where there was a difference, those that underwent surgery had lower Q of L scores than those undergoing radiation treatment or observation. When compared to a non-tumor control group, they found that being diagnosed with VS had a greater negative affect on Q of L than did treatment strategy. In the second study, using the same group of patients, there was no difference between the three treatment groups in regards to reports of long term dizziness symptoms.
So, the question as I see it? Are we really helping our patients by diagnosing them with a VS, or are they better off not to know? My personal feeling is that by the time a patient gets to my office, they want to know what is causing their symptoms if I can determine that. Knowing that they have a VS or AN may allow them to better understand their symptoms and stop them from undergoing endless, fruitless tests. The fact that they are in my office implies that they are symptomatic (although not necessarily a result of the tumor). The study authors suggest “ intervention should be reserved for patients with unequivocal tumor growth or intractable symptoms that are amenable to treatment.”
photo courtesy of http://anworld.com/