Georges Lamas, Catherine Vidal, Remi Hervochon, Charles Ambroise Valery, Frédéric Tankéré.
ENT and Otoneurosurgery Department
Pitié-Salpêtrière hospital group
Vestibular schwannoma (VS) accounts for 6% of intercranial tumours and 80% of cerebellopontine angle tumours. It is estimated that there are 13 cases per million people each year.
Management of vestibular schwannoma has considerably changed over the past ten years, in large part due to the development of magnetic resonance imaging (MRI) and the use of gamma knife treatment as a therapeutic tool.
The ease of access to MRI scans allows an increasingly earlier diagnoses of VS, which can sometimes be completely asymptomatic and small in size.
Together with traditional surgery, gamma knife surgery is a very real therapeutic contender for its treatment.
The main clinical signs suggesting a diagnosis of VS are:
- Progressive or sometimes sudden unilateral hearing loss.
- Unilateral tinnitus.
- Vertigo or balance issues.
All of these signs must be fully assessed and require an MRI scan to confirm the diagnosis.
MRIs requested for other reasons, such as headaches, are increasingly discovering VS by accident.
The interview allows us to find out more about the often-long journey leading to diagnosis. It is essential to look for auditory or vestibular events that are sometimes old and unexplored. This can help assess the age of the tumour and help us gain an understanding of the patient's history and current complaints: hearing loss, balance disorders, pain, or facial paralysis.
The clinical examination includes the usual ENT examination and explores the cranial nerves (facial musculature, corneal reflex, facial sensitivity, lingual, velar, and laryngeal motor skills, swallowing). It is concluded by a vestibular examination (search for nystagmus, segmental deviation).
Cochlear exploration will include tonal and vocal audiometry, a study of stapedial reflexes and auditory evoked potentials.
The vestibular exploration will study caloric reflectivity, otolithic evoked potentials, the videonystagmoscopy, and equitest.
The MRI, which confirms the diagnosis, specifies the size and location of the VS in relation to the fundus of internal acoustic meatus and the cerebelloponitine angle.
The tomodensitometric examination of the petrosal bone in thin slices studies the petrous structures, in particular the facial canal, the jugular gulf and the posterior semi-circular canal.
The facial electromyography and the blink reflex study indicate the impact of the neurinoma on the facial and trigeminal nerves.
The main factor is the size of the tumour. VS is graded using the international classification scale (grade 1 - intracanalicular tumour, grade 2 - tumour less than 2 cm in size at cerebelloponitine angle, grade 3 - tumour of 2 to 4 cm in the cerebelloponitine angle, grade 4 - tumour of more than 4 cm in the cerebelloponitine angle). Other classifications (Koos) favour the relationship of VS with the cerebelloponitine angle structures and seem more useful for predicting the difficulties of radio surgery or surgery (grade 1 - intracanalicular, grade 2 - no contact with the cerebral trunk, grade 3 - contact with the cerebral trunk, grade 4 - displacement of cerebelloponitine angle structures). The relationship of VS with the fundus of internal acoustic meatus is important, as is any possible previous neurinoma development.
Hearing, on the side of the tumour and contralaterally, is the second decisive factor. On the side of the tumour, it is necessary to grade the patient using the Gardner and Robertson classification scale: class A - loss of less than 30db in tone average and more than 70% in speech discrimination, class B - loss of less than 50db in tone average and 50% in speech discrimination, class C - loss greater than 50db in tone average and 50% in speech discrimination, class D - no hearing. Classes A and B are considered as beneficial hearing. Contralateral hearing is also an important decisive factor. In the event of severe contralateral involvement, a pre-implantation assessment and lip-reading training can be undertaken before the therapeutic decision is made. The auditory evoked potentials on the side of the tumour (range 1-3) reflect the degree of compression of the tumour on the cochlear nerve.
The age of the patient at the time of diagnosis is also a decisive factor. It is logical to think that the discovery of VS in a young patient must entail modifying the therapeutic management since the risks of tumour growth are greater. In a woman, pregnancy does not seem to influence growth unlike with many intracranial tumours such as meningiomas.
The results of the vestibular assessment determine the importance of post-treatment for vestibular syndrome. If the vestibule is destroyed, there is no problem. On the other hand, in the case of a more or less functional vestibule, surgery can temporarily cause significant transient discomfort. Results are more uncertain after GKS due to its unknown impact on vestibular function. Dizziness or severe balance disturbances may favour surgery due to the beneficial effects of vestibular neurectomy in this case.
Trigeminal involvement, such as paraesthesia or pain, is an important consideration. This involves compression of the nerve and can be increased by GKS or cured by surgery.
The involvement of facial motricity is globally rare in the clinical history of VS. In the event of large tumours, it makes the conservation of the facial nerve very uncertain. In the event of small tumours, it is important to call into question the diagnosis of VS and look for a facial schwannoma, an internal acoustic meatus meningioma or even a malignant lesion.
The general condition of the patient plays a major role in the treatment decision, even though the interventions are increasingly well tolerated. An anaesthetic assessment can be done to objectively analyse the problem.
Finally, after a presentation of the therapeutic possibilities, and the corresponding merits and disadvantages of each one, the patient’s wishes must be carefully considered
The different treatment options must be explained to the patient, who has often been saturated with information from websites with little scientific value.
Monitoring is justified by the low growth rate of many tumours. It is currently accepted that a small tumour (stages 1 and 2) should be monitored in the first instance. The predictive criteria for growth appear to be the initial size of the tumour upon radiological discovery and increases in this size during the first year of monitoring. Generally, during a 3-year follow-up period, one in two patients will have tumour growth which often goes hand in hand with hearing degradation. It is not known how long tumours need to be monitored. Some advance over a period of 5 years but there is not enough evidence to say this is certain. The two main monitoring pitfalls are actually those patients lost to follow-up over a period of time and hearing impairment in patients with good initial hearing. Could early treatment prevent hearing loss?
Gamma Knife Surgery is the second therapeutic option, which is increasingly used. Since its design by Lars Lekssel in 1951, Gamma Knife treatment has been subject to many refinements, making it more reliable and less iatrogenic. The principle is to deliver a significant amount of radiation to an identified area in just one session. The patient can be discharged the next day or even the same day. The effects spread over time, generally for a period of three years. The tumour remains in place and may become partially necrotic. MRI monitoring is mandatory for an undetermined period of time, in order to detect resumption of tumour growth. Adverse effects are possible and include hearing loss, worsening of vestibular problems and trigeminal neuralgia. Some rarer adverse effects include transient facial paralysis, intracranial hypertension, and malignant VS progression. We can only be sorry for the lack of information available to clearly demonstrate its long-term efficacy and reliable percentages relating to possible side effects. This is due to the very inhomogeneous nature of the information available and the variable quality of initial assessments and remote monitoring. Other types of radiation therapy are possible but more rarely used.
Surgery is the third management option. Types vary depending on the possibility of an attempt to conserve hearing.
The middle cranial fossa route has been widely used for small tumour ablation before small lesion monitoring came into play. First of all, this route is difficult due to the narrow access; a facial nerve in the foreground with the tumour underneath. However, it gave the trained teams very good results in terms of facial function and hearing conservation percentages, which varied from 30 to 70% depending on the size of the tumour, and the preoperative cochlear state and the very low recurrence rate.
The retrosigmoid route is widely used in attempts to conserve hearing, either systematically or for small. stage 1 and 2 lesions, and even small stage 3 lesions For these small tumours, the results on facial function are good and the percentage of hearing conservation very variable, with the same parameters as for the subpetrous route. Its main drawback is the frequency of residue left at the bottom of the internal acoustic meatus which requires close monitoring. The retro-labyrinthine route is a variant of the posterior petrous route that can allow better drilling of the internal acoustic meatus.
The trans-labyrinthine route has long been the most commonly used by otoneurosurgical teams. It partially sacrifices hearing due to the posterior labyrinthectomy but allows complete removal of larger tumours, although fragments adhering to the facial nerve may be left in place to maintain function. The risk of facial function damage depends on the size of the tumour but has decreased significantly within trained teams.
If we can give a few management rules based on consensus, each case is specific and must be discussed with the treatment providers and patient. The advantages and disadvantages of each option must be clearly presented.
Stage 1 is a matter of monitoring, especially since small tumours are the least progressive. An MRI should be repeated six months after the initial discovery of the lesion and then every year should it remain stable. The existence of disabling vertigo can lead to a surgical procedure, often requested by the patient, which allows the tumour to be removed and a vestibular neurectomy to be carried out. The surgical subpetrous or retrosigmoid approach will be chosen depending on the location of the tumour in the internal acoustic meatus and the surgeon's experience. Of course, in the event of significant hearing loss, a trans-labyrinthine route can be used.
Stage 2 poses the biggest therapeutic indication problem since all treatment options are possible. Radiological monitoring makes it possible to assess the growth of the tumour, but some criticise this method for allowing many tumours to grow and contributing to hearing degradation with no intervention. It is here that gamma knife surgery finds its place as a therapeutic indication, especially for certain age groups and in the event of surgical risk factors. In young subjects, we may prefer surgery which removes the tumour permanently, as this currently shows very favourable results for facial and hearing function which, while worse in the short term, tend to improve over time. This is due to the absence of invasive surgery on the fundus of the internal acoustic meatus which gives a good prognosis for hearing conservation, both for retrosigmoid surgery and GKS. Disabling vertigo favours a surgical route, as does poor hearing in younger subjects.
Stage 3, in principle, requires surgical intervention, except in patients for whom surgery poses a significant risk. With good hearing, small stage 3 tumours can still benefit from a retrosigmoid approach if the tumour respects the fundus of the internal acoustic meatus. In the event of poor hearing, and more advanced stage 3 cases with filled acoustic meatus, the trans-labyrinthine route is the best choice. Finally, for high-risk patients, GKS can be offered.
Stage 4 entails trans-labyrinthine surgery for otoneurosurgical teams. However, the retrosigmoid route is increasingly used in the event of useful hearing, but overall, despite the use of cochlear nerve monitoring, the results remain a little disappointing. It may be necessary to leave fragments on the facial nerve to respect it. These will then be monitored and treated by Gamma Knife in the event of growth.
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