ASSOCIATE PROFESSOR NIGEL BIGGS explains why many patients with small acoustic neuromas can be safely monitored.
Vestibular schwannoma, which is also known as acoustic neuroma, is a benign tumour of the vestibulocochlear (eighth) cranial nerve. Though its occurrence is uncommon (about 8% of all intracranial tumours) it can represent a significant health risk and burden to the individual and to the healthcare system.
Treatment dates to the first surgery undertaken in the 1890s. This has evolved over the second half of the 20th century with further refinements in surgery and development of stereotactic radiation to control tumour growth. Over the past 30 years there have been extensive publications on the advantages and disadvantages of treatment modalities for this tumour and argument over which gives the best outcomes in tumour eradication and facial nerve results.
The classic presentation of these tumours is an asymmetric sensorineural hearing loss. The size of tumour presentation however is very variable ranging from tiny tumours two to three millimetres in size to those significantly compressing the base of the brain, posing an imminent threat to life.
Tumour control and facial nerve preservation
When required, treatment of these tumours is complex and requires a multidisciplinary approach. As the tumour arises on the eighth nerve it is usually difficult to successfully treat these tumours without severe or total loss of hearing. The primary aims of treatment are control of the tumour and preservation of the facial nerve which is usually stretched over the surface of the tumour. It is recommended that due to the complex nature of treatment, these lesions be treated in institutions that have a large experience in their management.
Widespread access to sensitive imaging such as MRI scans has increased the detection of small tumours, often in older individuals. It is known through many natural history studies that many of the smaller tumours often grow very slowly and a significant percentage do not seem to grow at all. This has led to the questioning of the need for treatment in many cases. More recent studies have also started to focus on quality-of-life outcomes prioritising preservation of neurologic function over cure, changing the treatment dynamic of these lesions.
As an institution with more than 40 years of experience in treating acoustic neuromas, St Vincent’s Hospital Sydney has many patients on an active surveillance (watch and wait) program. From a personal cohort of almost 800 patients, we have more than 300 patients being monitored. Monitoring involves regular MRI scans – initially at yearly intervals – as well as clinical review, which can be in person or as a tele-consult.
Retaining useful hearing
Seventeen per cent of these patients have been continuously monitored for more than 10 years and a smaller number over 20 years. It is evident that a number of patients will never need treatment in their lifetime. One of the issues with monitoring though is the risk that hearing will deteriorate over time.
Analysis of our data in more than 250 patients found 63% had retained useful hearing on last review. This compares favourably to radiotherapy (>50%) and surgery (>90%). From a hearing perspective, patients often end up using CROS type hearing aids as loss of integrity of the cochleovestibular nerve prevents cochlear implantation in most cases.
The quality-of-life studies have demonstrated that any intervention – radiotherapy or surgery – does impact on a patient’s long-term quality of life. These impacts include hearing loss, imbalance, potential facial nerve weakness and pain. Radiotherapy (sometimes known as gamma knife) has slightly better outcomes in small to medium tumours but cannot be used for large tumours where surgery is the only option.
The final concern is what proportion of patients being monitored develop growth in their tumour requiring treatment. We have also analysed our data on patients being monitored and have demonstrated over a five-year period, that approximately one-quarter of patients will require treatment of some nature. The outcome of treatment in this group is no worse than those who require treatment initially.
With modern imaging and regular review it is clear many patients with small acoustic neuromas can be safely monitored with minimal impact on their quality of life.
About the author: A/Prof Nigel Biggs is chairman of the Department of Otolaryngology, Head and Neck and Skull Base Surgery at St Vincent’s Hospital, Sydney with a special interest in otology and skull base surgery. He has extensive experience in the management of acoustic neuroma having operated on more than 500 lateral skull base cases.
