What is wait and scan for vestibular schwannoma?
Wait and scan management of vestibular schwannoma is the observation of the tumour without active intervention. It forms with microsurgery, and radiation are the three options for the management of vestibular schwannomas. Wait and scan management is viable, as 20% to 50% of tumours do not grow over five years from diagnosis (1,2,3,4,5). Vestibular schwannomas are benign tumours of the nerves of the inner ear. The incidence is 4-5/100 000 of the population and has increased slightly since the implementation of magnetic resonance imaging (MRI). The trend is that tumours are discovered earlier when they are smaller. These factors make observation, referred to as wait and scan, a management strategy.
It is crucial that patients are compliant and adhere to the follow-up appointments, so the wait and scan management of vestibular schwannoma protocol should only be considered in motivated patients.
Risk of growth with wait and scan for vestibular schwannoma
Vestibular schwannomas are likely to grow within the first five years, with 50%-80% showing growth.(1,2,3,4,5) Whether linear or volumetric, the measurement method can impact the accuracy of assessing tumour growth. Linear measurements tend to underestimate changes in size compared to volumetric measurements. More extensive tumours and a faster growth rate indicate a higher chance of continued growth.
The long-term growth patterns may be continuous or intermittent, entering into periods of inactivity. They can grow slowly or fast. In 4% of cases, they can shrink and, in rare cases, when small, even disappear. The average growth rate is 2,9 mm/year.
Regardless of age at diagnosis, it is probable that sporadic vestibular schwannomas will grow at some point in a patient’s life, with most tumours showing growth post-diagnosis. Monitoring tumour size is crucial for timely intervention and management.
How does the wait and scan protocol for vestibular schwannoma work?
The findings from the initial MRI will provide crucial information about the size and location of the tumor. This information will help determine the appropriate follow-up protocol for monitoring the tumour (6).
The location of the tumour, whether it is intrameatal (within the internal auditory canal) or extrameatal (outside of the internal auditory canal), will impact the follow-up protocol.
This protocol applies to tumours with a maximal extrameatal size of 20mm.
Ideally, the same radiologists and audiologists should perform the MRI and hearing test. Screening hearing tests are not good enough, and diagnostic audiometry should always be performed. Maintaining a 100% word recognition score is a good indicator for hearing preservation (7,8). Active treatment with surgery or radiation is indicated in cases where rapid growth is demonstrated.
Which clinical parameters may indicate the growth potential of a vestibular schwannoma?
Unfortunately, there are no clinical parameters such as age, gender, size of lesion or location that will accurately predict growth in a newly diagnosed vestibular schwannoma. The only possible indicator for likely growth is a vestibular schwannoma with significant growth during the first year of observation.
Patients should be aware of possible symptoms of vestibular schwannoma that may occur during the observation period. The occurrence of symptoms during the observation period is likely to indicate growth, although symptoms like hearing loss can occur in the presence of a non-growing tumour. Other symptoms include tinnitus, vertigo, loss of balance, headaches and facial numbness. Any new, unexplainable symptom should be brought to the attention of the attending medical practitioner. In these circumstances, the MRI will most likely be ordered earlier.
In which patients can watch and scan of vestibular schwannoma be considered?
Wait and scan may be considered in:
- a known stable (not growing) tumour
- a slow-growing tumour with no symptoms
- elderly patients over 65 years, especially those with small tumours
- vestibular schwannoma in the only or significantly better hearing ear
- those with risks for anaesthesia or surgery
- those who cannot tolerate radiation
- small tumours with good hearing
- those who refuse treatment
What are the advantages of wait and scan for vestibular schwannoma?
The ultimate aim of wait and scan management of vestibular schwannoma is maintaining a good quality of life (QOL) for the patient (9,10). The QOL is better for the wait and scan management strategy than those who received upfront surgical or radiation treatment. Some of the advantages include the following:
- 20%- 50% of vestibular schwannomas will not grow in 5 years
- 50% of patients with good hearing and 55% of patients with serviceable hearing will preserve it at five years
- facial nerve outcomes are better with observation
- avoidance of surgical complications (usually early) and radiotherapy complications (usually late)
- no time off from work
- cost saving compared to surgery and radiation in the early and medium follow-up period
What are the disadvantages of wait and scan for vestibular schwannoma?
The following are considered as possible disadvantages:
- The further and rapid growth of the tumour may make treatment more difficult at a later stage
- Increase in hearing loss if the tumour is not removed or prevented from growing
- In younger patients where complications of microsurgery are related to the size of the tumour, allowing tumour growth with observation may be problematic later.
- In cases of intracannalicular (smaller) vestibular schwannomas where growth is allowed to maintain hearing, cochlear implantation may not be possible later
- a 15% risk of sudden hearing loss
- There is a 20% risk of vertigo that may be sudden and incapacitating.
- Anxiety and poor QOL in some patients, knowing that they have an untreated tumour
- The necessity for lifelong MRI and the potentially toxic accumulation of the gadolinium contrast medium in the body
Facial nerve disorders in wait and scan of vestibular schwannoma
Facial nerve weakness (paresis) is a rare sign of vestibular schwannoma (11). If present, another tumour, namely facial nerve neuroma, must be ruled out. The risk of developing facial nerve paresis in the watch and scan management group is 1-2.2%. Prompt diagnosis and management are crucial in such cases.
Headaches in wait and scan of vestibular schwannoma
Headaches are a frequent symptom in patients with vestibular schwannoma, affecting over 40% of individuals in the wait and scan group (11). These headaches can signal increased intracranial pressure, a serious complication requiring immediate medical attention. Monitoring and early intervention are crucial in managing this potentially dangerous condition.
Vertigo, dizziness and balance problems in wait and scan of vestibular schwannoma
Vestibular schwannoma can cause vertigo in 20% of patients, with an estimated 5-15% experiencing sudden onset without warning signs. This can make tasks such as driving, operating machinery, and working at heights challenging. Additionally, dizziness is expected in 50% of patients, and balance problems are expected in 60%, further impacting daily activities and safety and impairing quality of life.
The prognosis in wait and scan of vestibular schwannoma
The mortality of patients in the wait and scan management group of vestibular schwannoma is not well-documented, but is believed to be low. The main cause of death is expected to be related to complications such as hydrocephalus due to a large tumor causing increased intracranial pressure or other neurological issues. A Danish study of 624 patients, Mistarz et al. found that patients over 70 years of age had a mean survival of 9.2 years in the observation group compared to 11 years in the general population (12).
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