And suddenly there is a whistling, hissing, beeping and roaring in the ear. It becomes difficult to fall asleep because the sounds in the ear dominate one’s thoughts. Headaches often accompany this, and some sufferers also experience severe tinnitus, dizziness and nausea. The cause of this problem is what is known as a vestibular schwannoma, originally called an acoustic neuroma, a (usually) benign tumor in the inner ear canal at the exit of the vestibular nerve, which enters the cranial cavity. This relatively rare tumor most commonly affects people between the ages of 50 and 60. Statistically speaking, only 1–1.5 people in every 100,000 are newly diagnosed with a vestibular schwannoma each year. Diagnosis and treatment require a high level of medical expertise, as the utmost precision and skill are essential, particularly in the event of surgical intervention. The editorial team of the Leading Medicine Guide had the opportunity to speak with one of the world’s leading specialists in vestibular schwannomas, Professor Amir Samii, MD, from the International Neuroscience Institute® (INI) Hannover GmbH, to learn more about this tumor condition, which is unfamiliar to many.
The tumor itself develops from so-called Schwann cells, which insulate the cranial nerves in the brain, thereby accelerating the transmission of information between individual nerve cells. In a person with a vestibular schwannoma, these cells grow uncontrollably and rapidly, encasing themselves in a capsule of connective tissue, thereby separating themselves from the surrounding tissue. Why such tissue growth occurs remains unclear to this day. The use of mobile devices as a possible cause has now been ruled out. The condition is referred to as a vestibular schwannoma because the growth originates from the vestibular nerve (the nervus vestibularis). This nerve transmits information from the inner ear to the brain. Many patients are unaware for a long time that something is growing in their head that does not belong there. However, as soon as the first symptoms, such as noticeable ringing in the ears or hearing loss, become apparent, the first step is to visit an ear, nose and throat specialist.
The vestibular nerve, together with the acoustic (cochlear) nerve, forms the eighth cranial nerve, the vestibulocochlear nerve. This is the hearing and balance nerve and runs from the inner ear through the internal auditory canal and the angle of the cerebellopontine angle into the brainstem. The myelin sheath of the cranial nerves consists of connective tissue cells, known as Schwann cells, from which vestibular schwannomas arise, specifically when there is a genetically or sporadically caused loss of a tumor suppressor gene (these are genes whose products suppress the uncontrolled division of genetically damaged cells and can prevent the development of tumors).
To make a diagnosis, the patient’s external auditory canal and eardrum are examined. A hearing test is also carried out using tone, speech and brainstem audiometry (BERA test) to check the functionality of the auditory nerves, as well as an assessment of the sense of balance. Finally, a contrast-enhanced magnetic resonance imaging (MRI) scan provides information on how advanced the tumor is and its exact location.
The benign tumor can be identified by the following symptoms:
- Sensorineural hearing loss
- Sudden hearing loss
- Tinnitus
- Dizziness
- Nausea and vomiting
- Headache
- Facial nerve paralysis (nervus facialis)
- Sensory disturbances in the face
- Stiff neck
- Impaired vision (double vision)
When a vestibular schwannoma is diagnosed, there are three treatment options: watchful waiting, radiotherapy and surgery.
Several factors play a role in deciding which type of treatment makes the most sense. For example, it depends on the exact location of the tumor, its size and its growth pattern. The patient’s individual medical history and personal preferences should also be taken into account. There are essentially three treatment options:
- The tumor is monitored to see whether it continues to grow (known as ‘wait and scan’) and whether immediate treatment is necessary.
- The tumor is treated with radiotherapy.
- The tumor is surgically removed.
Assessment and classification of tumor size
I. Small intracanalicular tumor located solely within the internal auditory canal (meatus acusticus internus). < 10 mm. All three treatment options are possible. Tumor growth is monitored with regular MRIs and hearing tests. If hearing deteriorates, or the tumor suddenly grows significantly, radiosurgical or microsurgical treatment may be considered.
II. Primarily intracanalicular tumor with protrusion into the cerebellopontine angle, but without contact with the brainstem. < 20 mm. Here too, all three treatment options are possible.
III. Tumor mainly localized in the cerebellopontine angle with contact with the brainstem, but without compression. < 30 mm. Microsurgical removal should be the aim.
IV. Large tumor with compression of the brainstem and surrounding cranial nerves. > 30 mm. Neurosurgical resection is strongly recommended.
“Worldwide, the number of surgical procedures is declining. The ‘wait and scan’ approach is very popular. It must be borne in mind that tumors vary greatly from case to case. In some patients, the tumor remains stable for up to a decade, and hearing is not impaired. In other patients, a tumor can grow by up to 3 mm a year. The growth rate is determined by the tumor’s genetics,” begins Professor Dr Samii in our conversation. “In some patients, a vestibular schwannoma is discovered incidentally, for example following sudden hearing loss. The aim of the option of stereotactic and outpatient radiation treatment of the tumor using the so-called Gamma Knife is then to stop its growth,” explains Professor Dr Samii.
The Gamma Knife works with natural gamma radiation from 201 small cobalt-60 radiation sources. For this purpose, a radiation guidance system consisting of 201 radiation channels is milled into a steel block. With precision down to a tenth of a millimeter, the rays strike the tumor at a previously calculated point.
It must be borne in mind that every patient reacts completely differently to the diagnosis. “One patient explains that they cannot live with having something in their head that doesn’t belong there, while another patient wants to avoid any form of intervention at all costs,” says Professor Dr Samii, describing the various patient reactions. “Fundamentally, however, it must be noted that surgical removal of a tumor makes sense, as the patient is then cured. The reality is that almost every patient with a vestibular schwannoma will, sooner or later, lose their hearing on the affected side if they decide against surgery. Of course, there is a risk that hearing will be permanently damaged during the operation and the patient will suffer hearing loss, but depending on the size of the tumor and the pre-operative hearing quality, there is at least a high probability and a chance that it will be preserved under optimal conditions. “With radiotherapy, long-term results show that gradual hearing loss occurs,” explains Professor Dr Samii. Radiotherapy can also lead to long-term neurological effects, though these are rare.
If the tumor continues to grow unchecked, it may, in the worst-case scenario, lead to compression of the brainstem, which the patient will notice in the form of coordination problems. In the worst-case scenario, it can also lead to impaired cerebrospinal fluid circulation (liquor circulation disorder) – at which point a vestibular schwannoma can become life-threatening.
The microsurgical procedure.
The idea of having surgery on the head is not a pleasant one – after all, a hole is drilled into the head. Let us explain the procedure to help alleviate any fears. “The hole that is drilled into the patient’s head with a diamond drill to remove the tumor is about the size of a two-euro coin. The incision is usually made behind the ear, right at the hairline between the temporal bone and the cerebellum. To keep the opening small, the bone is removed step by step. After the procedure, the opening is then sealed again with bone cement, similar to dental surgery. The cement expands slightly when inserted into the opening, ensuring everything is completely sealed again,” says Professor Dr Samii, describing the process of opening and closing the skull.
Patients are usually very concerned about damage to the facial nerve (nervus facialis) during the operation, which can result in facial paralysis. “An experienced surgeon performs this operation without risking nerve damage. The accompanying neuromonitoring is extremely helpful, as it checks the patient’s nerve response every second during the operation and provides the surgeon with up-to-date information as the tumor is progressively hollowed out from the inside to destroy the tumor structure,” explains Professor Dr Samii confidently. For small and medium-sized tumors, at the INI in Hanover – the Center for Skull Base Surgery and Reference Center for Neurosurgery – the facial nerve can be preserved in almost 100% of cases with small tumors and in up to approximately 90% of cases with large tumors.
The risk of possible and usually only temporary facial paralysis is far outweighed by the risk of leaving the remainder of a tumor in the patient’s head.
Only temporary irritation of the facial nerve is possible. “We rarely leave a piece of the tumor capsule in place, but we do so if it is directly attached to the facial nerves and the nerve is so fragile and sensitive that the risk of injury appears too great. The remaining tumor can then be monitored regularly to observe its growth and decide whether radiotherapy or a second operation is required at a later stage,” concludes Professor Dr Samii on the preservation of the facial nerve.
The effort required in the operating theater is considerable.
At the INI Hannover, seven people are involved in the surgical removal of a vestibular schwannoma – from the surgeon and assistant doctors to the anesthesiologist and the scrub nurse. The procedure typically takes a total of 4–6 hours, with the opening of the skull alone taking 30–60 minutes. The patient’s head, positioned in a semi-sitting position, is then positioned in front of a surgical microscope throughout the entire operation. “Here at the INI, the patient stays in hospital for 5–7 days after the operation, and a subsequent recovery period of around four weeks is recommended before they can resume their normal daily routine,” says Professor Dr Samii. Minor side effects such as mild dizziness, pain at the scar site or headaches are to be expected, but these will subside. Mild balance disturbances are also possible initially. “The patient is then, of course, monitored, and this is repeated after one year,” explains Professor Dr Samii, who has now performed over 1,000 operations in the brain region, whether for vestibular schwannomas, epidermoids (malformation tumors along the skull) or meningiomas (meningeal tumors). As for vestibular schwannomas, 50–100 cases are treated at the INI Hannover each year.
Who pays for all this?
Private patients naturally receive 100% reimbursement of all costs if they wish to undergo surgery at INI Hannover with Professor Dr Samii, an internationally renowned specialist. Professor Dr Samii adds a valuable point on this: “We have a framework agreement with the Kaufmännische Krankenkasse Hannover (KKH), so that those with statutory health insurance also have the option of undergoing surgery at the INI through this. For all other health insurance providers, there is the option to submit an individual case application, so that if the provider approves, the operation will be carried out at the statutory rate (flat-rate fee).” A total of over 200 patients with statutory health insurance undergo surgery at the INI each year.
Visions for the future.
Looking to the future, Professor Dr Samii would like to see greater predictability. “It would be so helpful if we could provide an even more precise prognosis regarding tumor growth and had more information through genetic sequencing. Work is also underway on better options for even better hearing preservation. This requires even more detailed monitoring to optimize the preservation of all functions. In any case, the patient’s quality of life is always the top priority,” emphasises Professor Dr Samii, who always takes a personal and individual approach to caring for his patients, thus concluding our conversation.
Professor Dr Samii, thank you very much for the insight into this rather little-known yet important topic!
