Vestibular Schwannoma (Acoustic Neuroma)

A vestibular schwannoma, also commonly referred to as an acoustic neuroma, is a usually benign and slow-growing tumor arising from the Schwann cells of the vestibular nerve. The tumor most commonly originates within the internal auditory canal and may extend from there into the cerebellopontine angle.

The cochlear nerve and the facial nerve are located in its immediate vicinity. With increasing tumor size, the brainstem, cerebellum, and additional cranial nerves may also become affected.

For decades, the treatment of vestibular schwannomas has been one of the major areas of expertise in skull base surgery at the International Neuroscience Institute (INI) Hannover and within the neurosurgical school founded by Professor Madjid Samii.

The objective of modern vestibular schwannoma surgery extends far beyond the removal of a tumor alone. The aim is to achieve the most definitive possible tumor control while preserving neurological function to the greatest possible extent - particularly facial nerve function and, whenever feasible, hearing - and to restore function when it has already been impaired or lost.

Symptoms

The clinical presentation of a vestibular schwannoma can vary considerably and depends, among other factors, on tumor size, location, and growth rate.

The disease frequently begins with unilateral hearing loss, tinnitus, or disturbances of balance. Vertigo, gait instability, or a sensation of pressure in the affected ear may also occur.

With larger tumors, additional cranial nerves may become involved. Possible symptoms include facial sensory disturbances, impairment of facial movement, or swallowing difficulties. Very large vestibular schwannomas may compress the brainstem and cerebellum and interfere with cerebrospinal fluid circulation. In these situations, surgical treatment may become urgent.

Diagnosis and Preoperative Planning – More Than Measuring Tumor Diameter

The diagnostic foundation is high-resolution magnetic resonance imaging (MRI) of the brain and skull base, with dedicated visualization of the internal auditory canal, cerebellopontine angle, cranial nerves, and the relationship of the tumor to the brainstem and surrounding vessels.

At the INI, detailed surgical planning also includes high-resolution CT imaging of the temporal bone. While MRI primarily demonstrates the tumor, cranial nerves, and surrounding soft-tissue structures, CT provides essential information about the individual bony anatomy of the skull base and internal auditory canal. These anatomical details can be highly relevant when planning the surgical approach and performing safe microsurgical dissection.

A differentiated assessment of hearing and the function of the involved cranial nerves complements the imaging studies.

During follow-up, the maximum tumor diameter alone is not sufficient to characterize the biological behavior of a vestibular schwannoma. Changes in tumor volume and growth rate, as well as the individual relationship of the tumor to the cochlear nerve, facial nerve, brainstem, and other anatomical structures, are particularly important.

Treatment decisions and, when surgery is required, surgical planning are therefore always based on an integrated assessment of the clinical examination, functional diagnostics, high-resolution MRI, and the individual bony anatomy demonstrated by temporal bone CT.

Not Every Vestibular Schwannoma Requires Immediate Treatment

A diagnosis of vestibular schwannoma does not automatically mean that surgery or radiation treatment is required.

Particularly in patients with small, asymptomatic, or only mildly symptomatic tumors, controlled observation - “Watch & Scan” - may be an appropriate initial strategy. This involves MRI examinations as well as clinical and audiological assessments at defined intervals.

If there is no relevant tumor growth and neurological function remains stable, this strategy may be continued for an extended period. If tumor growth is documented or neurological or audiological function deteriorates, the treatment strategy must be reassessed.

The Patient Is an Essential Part of the Treatment Decision

One of the particular characteristics of vestibular schwannoma is that, especially for small and medium-sized tumors, more than one medically reasonable treatment strategy may exist.

The appropriate decision therefore cannot be based on an MRI scan alone.

People respond very differently to the diagnosis of a tumor. Some patients are entirely comfortable with monitoring a vestibular schwannoma by regular MRI examinations over many years. For others, the knowledge of living with an untreated tumor and the uncertainty regarding its future growth represent a considerable psychological burden.

Other patients initially need time to process the diagnosis, understand the different treatment options, or obtain a second opinion. Whenever the medical situation permits, they should be given that time.

The responsibility of a specialized center is therefore not simply to recommend a particular treatment. It is to explain the different options, their opportunities, risks, and long-term consequences in an understandable manner and to develop, together with the patient, a decision that is appropriate both for the tumor and for the individual person.

The Patient’s Expectations Also Influence the Surgical Strategy

This individualized treatment philosophy does not end once the decision for or against surgery has been made.

Before microsurgical treatment, a detailed personal discussion about the patient's expectations and priorities is particularly important. Patients differ considerably in the degree of functional risk they are prepared to accept in pursuit of the most complete possible tumor removal.

Occupation, personal circumstances, age, residual hearing, function of the contralateral ear, particular requirements regarding facial expression, balance, or other neurological functions may all play an important role in the individual decision.

Not every conceivable situation can be captured in a predefined algorithm.

The surgeon must therefore understand the patient's personal priorities before the operation begins. Only then can these priorities genuinely influence surgical decision-making if, during the procedure, a situation arises in which maximal tumor removal must be weighed against a potentially increased functional risk.

In this way, the operation is guided not only by an MRI image or by a general surgical objective, but by the individual person being treated.

Microsurgery: Complete Tumor Removal and Preservation of Function

When surgery is indicated, the fundamental microsurgical objective is complete tumor removal with the best possible preservation of neurological function.

In principle, complete tumor removal can be regarded as equivalent to cure, since the risk of recurrence after complete removal is very low (<1% in large surgical series).

From our perspective, there is therefore no fundamental contradiction between radical tumor removal and preservation of function.

If a vestibular schwannoma can be completely separated from the facial nerve, cochlear nerve, brainstem, and surrounding vessels without exposing the patient to a disproportionate functional risk, complete removal is the objective.

A deliberately planned incomplete resection from the outset is therefore not the fundamental surgical treatment concept at the INI.

At the same time, radicality must never become an end in itself.

The decisive situation may only become apparent during surgery. Some tumors, despite their considerable size, can be completely separated from the functionally important structures. Others may be exceptionally adherent to the facial nerve, cochlear nerve, brainstem, or critical vessels at one small but decisive area.

This is where the true art and experience of vestibular schwannoma surgery become apparent.

The experienced surgeon begins with the objective of complete tumor removal and determines, based on the actual microsurgical anatomy, continuous neurophysiological monitoring, and the functional priorities previously discussed with the patient, how far dissection can responsibly be continued in a critical situation.

In an exceptional situation, it may therefore be appropriate to leave an extremely thin layer of tumor attached to a critical structure if its removal would carry a disproportionate risk of permanent functional loss.

Such a decision is not a predetermined standard strategy. It is an individualized intraoperative decision made to protect function.

Experience and the Samii School of Vestibular Schwannoma Surgery

Few areas of neurosurgery are as dependent on the personal experience of the surgeon and the entire treatment team as microsurgical treatment of vestibular schwannoma.

Modern microscopes, neuroendoscopy, and intraoperative neurophysiological monitoring are essential tools. They do not, however, replace the experience gained from personally performing a very large number of operations.

The history of modern vestibular schwannoma surgery in Hannover is inseparably linked to Professor Madjid Samii.

Professor Samii is one of the international pioneers of microsurgical vestibular schwannoma treatment. Over several decades, he developed and refined the retrosigmoid microsurgical approach and surgical techniques designed to achieve the most complete possible tumor removal while simultaneously maximizing preservation of cranial nerve function.

His personal experience includes more than 5.000 vestibular schwannoma operations, representing one of the largest individual surgical experiences in this field worldwide.

The classic Hannover series of 1.000 consecutively operated vestibular schwannomas became international reference publications for modern microsurgery, facial nerve preservation, hearing preservation, and intraoperative neurophysiological monitoring.

Professor Madjid Samii has also trained generations of neurosurgeons from numerous countries, thereby establishing an international school of skull base surgery.

Continuity and Further Development – Professor Amir Samii

Professor Amir Samii had the particular privilege of becoming intensively involved in vestibular schwannoma surgery, its different surgical approaches, and microsurgical techniques from the early 1990s onward, initially through scientific work.

For more than 25 years, he worked continuously with his father and teacher, Professor Madjid Samii - first as a student and assistant, and later as an independent surgeon and partner in the further development of microsurgical techniques and treatment concepts.

His personal experience today comprises more than 1.000 vestibular schwannomas and cerebello pontine angle tumors treated microsurgically, in addition to a very large number of complex operations performed together with Professor Madjid Samii.

This represents an exceptional continuity of surgical experience spanning more than 25 years - from training and joint clinical and scientific work to the continued development of vestibular schwannoma surgery at the INI and through international collaborations today.

The common objective has remained unchanged while the techniques and concepts have continued to evolve: the most complete possible tumor removal with the best possible preservation of neurological function.

The Retrosigmoid Approach – One Approach for Tumors of Every Size

For microsurgical removal of vestibular schwannomas, we generally use the retrosigmoid approach at the INI. Through a comparatively small opening behind the ear, this provides a direct microsurgical route to the cerebellopontine angle and internal auditory canal.

This approach is an essential component of the surgical technique developed and refined by Professor Madjid Samii over several decades. As part of his pioneering work in vestibular schwannoma surgery, Professor Samii used and analyzed the different established surgical approaches over many years -including the translabyrinthine approach and the middle fossa approach - both personally and in close collaboration with ENT colleagues, evaluating their respective possibilities and limitations.

Based on this comprehensive comparative experience, the retrosigmoid approach evolved into his preferred surgical concept and has been continuously developed and refined over decades.

A major advantage is that the retrosigmoid approach can be used for vestibular schwannomas of every size - from small tumors located predominantly within the internal auditory canal to giant vestibular schwannomas with extensive cerebellopontine angle involvement and significant brainstem compression.

It permits comprehensive visualization of the anatomical structures relevant to surgery and thereby provides the conditions required for radical or complete tumor removal, whenever the individual relationship of the tumor to functionally important nerves and vessels allows this to be achieved safely.

At the same time, depending on the functions still present before surgery and the individual anatomical situation, the approach allows a consistently function-preserving strategy. This applies particularly to the facial nerve and, when useful hearing is present preoperatively, to the cochlear nerve and therefore the possibility of hearing preservation.

Throughout tumor dissection, the cranial nerves at risk are continuously monitored neurophysiologically. The microsurgical strategy is continuously adapted to the visible anatomy, the neurophysiological monitoring findings, and the functional priorities discussed with the patient before surgery.

For us, therefore, the retrosigmoid approach is not merely a surgical route. It provides the anatomical basis for a surgical philosophy that combines two objectives:

the most complete possible removal of the tumor and the best possible preservation of existing neurological function.

Stereotactic Radiosurgery and Gamma Knife

For selected smaller vestibular schwannomas, stereotactic radiosurgery - for example Gamma Knife treatment - may represent a therapeutic option.

The objective in this situation is not removal of the tumor but long-term control of further tumor growth.

Suitability depends particularly on tumor size, location, documented growth, hearing function, age, and the individual preferences and circumstances of the patient.

For large vestibular schwannomas with significant brainstem compression, radiosurgery alone is generally not an appropriate alternative to microsurgical decompression because the existing mass effect is not immediately relieved.

Radiosurgery may also represent a later option for a deliberately retained small tumor remnant if that remnant subsequently demonstrates relevant growth.

Here again, the principle is that the technical availability of a treatment does not determine the strategy - its individual necessity does.

Large and Complex Vestibular Schwannomas

The INI has particular experience in the treatment of very large and complex vestibular schwannomas.

As tumor size increases, the anatomical relationships can change dramatically. The brainstem, cerebellum, facial nerve, cochlear nerve, and additional cranial nerves may be displaced, flattened, or partially or completely covered by the tumor.

In these tumors, the microsurgical experience of the surgeon, controlled stepwise reduction of the tumor volume, identification of the anatomical tissue planes, and continuous neurophysiological monitoring are of decisive importance.

Even very large tumors can, under appropriate conditions, be completely removed. Tumor size alone is therefore not a reason to pursue an incomplete resection as a matter of principle.

Revision and Salvage Surgery – A Particular Focus at the INI

Another particular area of expertise is the treatment of patients whose vestibular schwannoma has already undergone previous treatment.

These situations include residual tumors that continue to grow after previous incomplete surgery; recurrent tumors after previous microsurgery; vestibular schwannomas that continue to grow after radiosurgery or stereotactic radiation; tumors that progress after previous incomplete surgery followed by radiation treatment; and complex cases with pre-existing deficits of the facial nerve, cochlear nerve, or other cranial nerves.

These so-called salvage procedures are among the most demanding operations in skull base surgery.

Following previous surgery, natural tissue planes may be altered or obliterated by scar formation. Following radiation treatment, the tumor, cranial nerves, vessels, and brainstem may become more firmly adherent to one another. When previous surgery and radiation are combined, these changes can make microsurgical dissection particularly challenging.

In precisely these situations, extensive personal surgical experience and the ability to adapt the operative strategy to the actual anatomy encountered during surgery are crucial.

The Facial Nerve – Preservation, Reconstruction, and Reanimation

Preservation of facial nerve function is one of the highest priorities in vestibular schwannoma surgery.

However, the INI treatment concept does not end when a patient presents with an existing facial palsy or when the nerve has already been damaged by previous treatment.

Depending on the type, location, and duration of the injury, different reconstructive options are available.

Whenever possible, nerve continuity may be restored by direct microsurgical reconstruction or by an interposition nerve graft. If a functionally usable proximal facial nerve stump is no longer available, nerve transfer procedures - such as hypoglossal-facial nerve anastomosis - may be considered.

In patients with long-standing facial palsy, additional secondary reconstructive and plastic surgical procedures for facial reanimation may be required.

The objective is not merely to produce some form of movement. The goal is the most natural functional rehabilitation possible, with improvement of facial symmetry, facial expression, and, in particular, reliable eye closure.

Hearing Preservation and Auditory Rehabilitation

Preservation of natural hearing, whenever anatomically and functionally possible, is an important objective of treatment.

A distinction must be made between anatomical preservation of the cochlear nerve and preservation of useful hearing function.

For this reason, the possibilities for hearing preservation and, where necessary, subsequent auditory rehabilitation are considered during surgical planning together with our ENT, neurotological, and audiological colleagues.

If functionally useful natural hearing cannot be preserved, treatment does not end with tumor control.

Depending on which structures of the auditory system remain anatomically and functionally available, different options for auditory rehabilitation may be considered. These include, in particular, the cochlear implant (CI) and the auditory brainstem implant (ABI).

In addition, the INI and its scientific and clinical partners have for many years been involved in the development and advancement of direct auditory neuroprostheses, including the Auditory Midbrain Implant (AMI) and the Auditory Nerve Implant (ANI).

The concept of vestibular schwannoma treatment therefore increasingly extends beyond tumor surgery alone toward a comprehensive strategy of tumor control, preservation of function, and restoration of function.

An Individual Decision – for an Individual Person

There is no single treatment strategy for vestibular schwannoma that is equally appropriate for every patient.

A small stable tumor represents a different situation from a growing tumor in a young patient with good hearing. A patient with only one functionally hearing ear has different priorities from a patient with normal bilateral hearing. A giant tumor with brainstem compression requires a different strategy from a small intracanalicular tumor. And a tumor that has already undergone multiple operations or radiation treatment presents an entirely different challenge.

The people living with these diagnoses are equally individual.

Detailed personal consultation is therefore an essential part of our treatment philosophy.

We want to understand what is important to the individual patient, what expectations they have regarding treatment, and which risks they are prepared to accept in pursuit of which goals.

This information is relevant not only when deciding between observation, radiosurgery, and microsurgery. It may also influence decisions made by the surgeon during the operation itself.

The optimal treatment of a vestibular schwannoma therefore arises from the interaction of scientific evidence, modern technology, extensive personal surgical experience - and an understanding of the individual needs of the patient.

Our Treatment Principle

The treatment of vestibular schwannoma is, for us, more than a choice between observation, surgery, and radiosurgery.

It combines maximum tumor control, the best possible preservation of function, the individual expectations and priorities of the patient, and—where necessary—the restoration of lost function.

From tumor control to preservation and restoration of function.

Scientific Publications on Vestibular Schwannoma