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may take place over a period of months as the swelling gradually settles with time. If there is any residual tumour, this is checked with serial imaging, and any further growth then typically treated with radiation therapies.
Symptoms of a skull base tumour The symptoms appear slowly as the tumours grow and specific symptoms will depend on the type, location and size of the tumour. Common symptoms include: l weakness l hearing loss l numbness l vision loss l double vision l problems with balance
A subgroup of these tumours can sometimes be diagnosed incidentally when scans are performed for other reasons. The ideal form of imaging for an accurate diagnosis is an MRI of the head with contrast medium. This will show the characteristics of the tumour, and its relationship with the surrounding brain structures. Once a diagnosis is made, a treatment plan can then start to be formulated.
Swelling or oedema caused by skull-base tumour In some cases, the scan may reveal that the tumour is causing swelling in parts of the brain, and this is called ‘oedema’. This oedema can cause symptoms in addition to those that result purely from the pressure of the tumour itself. If the oedema is significant and causing symptoms, treatment with steroid medication, such as ‘dexamethasone’ may be needed for a period of time as decided by the clinician. However, because long term use of steroids is associated with medical complications such as weight gain and osteoporosis, their use is usually restricted to short periods.
The majority of tumours, particularly those of a smaller size, are suitable for treatment with stereotactic radiosurgery techniques such as Gamma Knife radiosurgery. As this has the benefit of being non-invasive, it has a lower risk of injury – for example, to the facial nerve, in the region of 1% of cases or less.
Skull base tumours treated with Gamma Knife Vestibular schwannoma and meningioma are both examples of benign skull base tumours that have similar behaviour and treatment options, where complex management approaches are often required, including Gamma Knife radiosurgery.
Vestibular schwannoma Vestibular schwannoma (also referred to as acoustic neuroma) are formed by the over production of the Schwann cells that support and insulate the vestibular and cochlear nerves. As such these most commonly present with balance issues, hearing loss or tinnitus on one side. As they grow larger, these tumours can press on the trigeminal nerve and cause facial numbness and in some cases, shooting pains. These tumours grow approximately 1 to 2 mm a year, and are primarily treated with either surgical removal or focussed radiation treatments. The location of these tumours significantly affects the decision on what treatment is best. They grow in a confined space between the hearing structures of the ear and the brainstem, called the cerebellopontine angle. There is very little space here to accommodate tumour growth or swelling, and there are many critical nerves and blood vessels.
The brainstem itself is densely packed with fundamental neural structures. In this context, the management of these tumours should be guided by an experienced multidisciplinary team with the ability to provide all types of treatment to a very high level. The main difficulty with treating vestibular
schwannoma is the proximity of the nerve to the face on that side. This ‘facial nerve’ is immediately adjacent to the hearing and balance nerve, and because of this it becomes progressively stretched by tumour growth. This stretching happens slowly which means that the nerve is rarely impacted and, in fact, can be flattened very significantly by the tumour without any loss of function. However, because it is compressed, it is susceptible to injury from treatments for the tumour resulting in facial weakness or, in some cases, complete paralysis. In the first instance, it is usual best practice
to monitor the tumour and assess its behaviour with a repeat scan within six months. A significant proportion of tumours, particularly those of a smaller size, do not grow, and these may be followed up long term with an MRI scan once a year. If the tumour is stable for a number of years, this interval can be increased.
Treating large vestibular schwannoma tumours Large tumours causing swelling in the “normal” brain usually require surgical intervention. If it is of a very large size, up to 4cm for example, the tumour may prevent normal brain fluid exiting the brain, and this is called ‘hydrocephalus’. When this happens, a ventriculoperitoneal shunt can be inserted in order to bypass the obstruction and this carries cerebrospinal fluid (CSF) from the brain to the abdomen, where it is absorbed. For tumours above 2.5cm, surgery is usually considered in order to remove as much of the tumour as possible and relieve the pressure on the brain. Such surgery is usually performed in specialist centres with sufficient expertise in the management of such tumours. Due to the technical demands of this treatment, these
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www.clinicalservicesjournal.com I February 2024
Image provided courtesy of Elekta
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