As an audiologist I was taught about the hearing test early on. Though I do have to keep my eye out for many disorders (as you have seen in my past blogs), there is one condition that always seems to be on the top of my mind, Acoustic Neuroma, or Vestibular Schwannoma. This is a slow-growing, (1.5 mm a year) benign tumor (non-spreading, non-malignant) found on the acoustic nerve from the cells making the myelin sheath.
The VIII cranial nerve, the Acoustic Nerve, controls hearing and balance and lies very close to the VII cranial nerve, the Facial Nerve, which supplies the neural pathway for motion to the muscles for facial expression. In fact, both cranial nerves pass through a bony canal, which is named the internal auditory canal. Early symptoms are hearing loss, which is worse on one side (in most cases if the tumor is on only one side, type 1) as well as tinnitus on the affected side. Later, as the tumor grows, balance and facial muscle symptoms can develop. Alan Desmond has discussed audiometric testing in detail in a 2011 post.
When I look at the numbers, I see that only a very small number of individuals develop this condition, yet it seems that this is the top worry whenever I test. A study in Denmark, published in 2004, had a very large sampling showing 2 people out of 100,000 will have an acoustic tumor. Some argue that the incidence is rising, but this is most likely due to better diagnostics, including the advancements of MRI scanning and better referrals for those experiencing symptoms. The general consensus is that both sexes are affected equally and is usually diagnosed between the ages of 30 and 60. There is usually only one side affected by the tumor. David Kirkwood reported last year how an ENT was sued over missing an acoustic tumor, which is most likely why it is on my mind during diagnostic testing. I would not want to be the provider to miss this.
How does a tumor form? It is not entirely understood, but some suggest genetically there is a breakdown in tumor suppression genes that allows the tumor to grow. There is no concrete proof that an external factor such as cell phones create these tumors. There is a condition, Neurofibromatosis (NF2), which is a genetic disorder affecting 1 in 50,000 births. With this condition, tumors grow in both sides of the head on the acoustic nerve. If this occurs there is a chance of losing the hearing on both sides leading to complete deafness.
Treatment consists of three areas – observation, radiation and surgical removal. Since the tumor surrounds the nerve, a specialist should be used for consultation. Neurosurgeons and/or neurotologists are surgeons who specialize in the ear area and perform delicate surgeries. They depend on a team of other providers to cover other areas that may be affected. No one treatment is right for every patient. If the tumor is very slow growing and the patient is not in good health, the best option might be to watch and wait.
Surgical removal may be an option in the case of NF2 with a smaller tumor or faster growing tumors in young healthy persons. There are many type of surgeries explained here.
The last option is radiation. There are two techniques – one delivered as a single dose, stereotactic radiosurgery (SRS), and the other is multi-session fractionated stereotactic radiotherapy (FSR). Each is targeted to stop growth and kill the tumor (necrosis). With radiation there is a chance for some hearing to be retained in the treated ear, which must be monitored during and after treatment.
The Acoustic Neuroma Association provides education and support to those faced with this type of condition. The ANA also has a Facebook page.
