Incidence and prevalence of vestibular schwannoma

Incidence and prevalence of vestibular schwannoma

The difference between incidence and prevalence

Incidence refers to the number of new cases of a specific disease or condition occurring within a particular time period. It gives us an idea of how frequently new cases are developing within a population.

Prevalence, however, refers to the total number of existing cases of a disease or condition within a population at a given time. It gives us an idea of how widespread a particular disease or condition is within a population.

 

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What a patient wants to know

A patient wants to know the chances that they would have developed a sporadic vestibular schwannoma in their lifetime. Prevalence indicates this risk. According to the literature, the prevalence likely exceeds 1 out of 500 people (1). This means that at least 1 out of 500 people will develop a vestibular schwannoma in their lifetime.

Sporadic versus non sporadic vestibular schwannomas

A sporadic vestibular schwannoma  develops in a patient without a family history or genetic susceptibility (such as neurofibromatosis type 2 or NF2) of vestibular schwannoma.  Of all vestibular schwannomas diagnosed, 95% are sporadic and solitary.

The incidence of vestibular schwannoma

The global traditional quoted incidence of 1 per 100,000 population is wrong. This is an old figure and an underestimation. The incidence of sporadic VS is closer to 5 per 100,000 people. In elderly patients > 70 years, the incidence is estimated to rise to over 20 per 100,000 of the population (1). One reason for this is the increased availability of magnetic resonance imaging (MRI). The life expectancy of people is also growing. Another consequence of increased MRI is that vestibular schwannoma has become smaller with diagnosis.

Vestibular schwannoma and other brain tumours

Vestibular schwannomas account more or less for:

  • 6% of all tumours in the skull
  • 30% of all tumours of the brainstem
  • 85% of all tumours in the cerebellopontine angle (CPA)
  • >90% of all tumours in the internal auditory canal (IAC)

The mean age of diagnosis

The mean age of diagnosis of sporadic vestibular schwannoma is 60 years. It has increased because life expectancy has risen, and magnetic resonance imaging has become readily available. Some vestibular schwannomas are picked up incidentally (without being symptomatic) in elderly patients who receive MRI for unrelated conditions. It can rarely occur in children.

Gender difference

The incidence of  vestibular schwannoma is equal between men and women (2). An interesting finding is the increase in males diagnosed with sporadic vestibular schwannoma in one study(3). Denmark has one of the world’s largest and most comprehensive databases on vestibular schwannoma. They found that more women were diagnosed from 1976 to 1993, followed by 14 years with equal distribution between sexes (1994 – 2007). In contrast, more men were diagnosed from 2008 and onwards. Research on this topic is ongoing.

The size of the vestibular schwannoma at diagnosis

The size of vestibular schwannoma at diagnosis has decreased (3). Again, looking at the Danish database, it is self-evident. In 1976, the average size at diagnosis was 30mm. In 2015, the average size decreased to 7mm. This is because more MRIs are performed, and therefore, some vestibular schwannoma are picked up before displaying symptoms. Vestibular schwannomas are diagnosed at an earlier stage nowadays. MRI performed for other conditions may show an incidental vestibular schwannoma (without symptoms).

MRI image of a large right sided acoustic neuroma
A vestibular schwannoma
Intracannaliculur acoustic neuroma
Vestibular schwannoma often causes tinnitus

The shift from neurosurgeon to neurotologist in vestibular schwannoma​

Due to the size and intimate connection with the brainstem, vestibular schwannoma was considered a neurosurgical disease in 1976. The smaller and most often intracannalicular (in the internal auditory canal) size at diagnosis in 2024 has shifted the responsibility back to the neurotologist.

References