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What is Skull Base?

and what to expect when visiting your skull base centre

 

The skull base is divided into 3 discrete zones namely the anterior, central and lateral regions.  It stretches from the nose and nasal cavities to the foramen magnum that encompasses to spinal cord within the occipital bone, and from ear to ear laterally. Skull base tumours comprise a spectrum of pathology that may affect any part of the skull base.  The skull base is traversed by major vessels, all the cranial nerves and is in close proximity to the brain stem.  Tumours arise either from the tissues that make up the skull base or from those adjacent to it for example the paranasal sinuses or structures in the upper part of the neck.  

Patients with skull base tumours present with a variety of symptoms that reflect the site of origin and the areas into which the tumour has infiltrated. Typical symptoms include nasal obstruction, epistaxis, visual loss and diplopia, facial pain or numbness, hearing loss, vertigo, facial paralysis, speech and swallowing problems and limb symptoms. While a few of these symptoms are reversible by treatment, a much larger number are preventable. 

The management of skull base tumours is complex and requires the collective experience of a multidisciplinary team.  This team will include ENT Skull Base surgeons, Neurosurgeons, Clinical Oncologists, Plastic surgeons, Radiologists, Maxillofacial surgeons, Ophthalmic surgeons, Neuropathologists and Skull Base Nurse Practitioners.  These tumours present one of the most difficult management challenges because of their position within the head close to important structures.

It is not always necessary to treat these tumours and therefore active surveillance might well be the best decision. Surgery and or radiotherapy will be considered and discussed in detail with you if relevant in your case.  The multidisciplinary team will meet to discuss your case before they meet you in clinic.  You will have an opportunity to meet all the doctors involved in your care and they will be able to answer any questions that you or your family have.  

Below are some information sheets covering the more common tumours that skull base surgeons manage.  The information is designed to be a general overview and will be added to by the centre looking after you.

Managing skull base tumours not only includes treatment of the tumour but also the symptoms caused by that tumour.  Your centre will be able to offer specialist hearing, balance, mobility, vision, speech and language therapy so if concerned do ask. 

Skull Base Surgery

Not all tumours of the skull base require surgery but when surgery is required it is usually performed by a team comprising an ENT Skull Base surgeon and a Neurosurgeon. Sometimes other surgeons are also involved. This might include a Plastic surgeon, Maxillofacial surgeon and/or Ophthalmic surgeon. The type of surgery performed depends on the site, type and size of the tumour as well as the expertise of the team.

Procedures are usually divided according to whether the tumour is involving the front part of the skull base (anterior cranial fossa) or the middle part of the skull base (middle cranial fossa).


 

Anterior Cranial Fossa Operation:

– Endoscopic Sinus Surgery
This type of surgery is usually performed for the removal of tumours involving the nasal cavity, anterior and central skull base.

The operation is performed using special telescopes (also called endoscopes) through the nostrils. This means there are no scars and the stay in hospital is usually short. Two surgeons work together so that maximum access and tumour removal is possible.

– Craniofacial Resection
For larger tumours that involve the anterior skull base, it is sometimes necessary to remove a larger portion of the bone around the skull base to ensure that the tumour is completely removed. This requires a cut either just below the eyebrow, in the hairline over the top of the head or in the gum above the front teeth.


Middle Cranial Fossa Operations:

There are three main operations performed to remove tumours involving the middle or back portion of the skull base.

– Translabyrinthine Approach
This is the most commonly performed operation and is used mainly for the removal of vestibular schwannoma (acoustic neuroma). It requires removal of most of the bone around the ear and as a result the hearing is lost on the operated side. However, the majority of patients having this sort of surgery have poor hearing already. By removing the bone, the lining of the brain is exposed and can be opened with minimal brain retraction in order to enable removal of the tumour.

– Retrosigmoid Approach
This approach is an alternative to the translabyrinthine approach. It involves cutting a bony window in the skull behind the ear. This technique is useful in patients with small to medium sized tumours and good hearing as it sometimes allows preservation of hearing.

– Middle Fossa Approach
This approach involves cutting a window in the bone of the skull immediately above the ear. It can be used to remove small tumours in patients with good hearing as it sometimes allows preservation of hearing.


Skull Base Radiotherapy

Radiotherapy is the use of high energy X-rays to treat tumours. It can be delivered as a single or small number of treatments and this is normally called stereotactic radiosurgery. Alternatively it can be divided into 30 treatments (fractions), which are given daily (Monday to Friday) for several weeks; this is called fractionated stereotactic radiotherapy. To decide which form of radiotherapy is best for you involves an outpatient appointment, look at your MRI scans to assess the size of your tumour, its location and also to consider your own personal preference.


What is the aim of radiotherapy?

Radiotherapy aims to stop benign tumours growing any bigger and for some patients will actually make them shrink, although this may take years following treatment. Radiotherapy in these situations will not remove your tumour. Radiotherapy might also be offered as a treatment after a more aggressive tumour has been excised. Occasionally radiotherapy is offered as palliative treatment to reduce symptoms but not with the intention of cure.

Fractionated stereotactic radiotherapy

The benefits of radiation are not immediate but occur over time. Aggressive tumours, whose cells divide rapidly, tend to respond quickly to radiation. Following radiotherapy, the abnormal cells die and the tumour may shrink. Benign tumours, whose cells divide slowly, may take several months to a year to show an effect.

Radiotherapy is split into a number of treatments called fractions that are given over several weeks. Delivering a small fraction of the total radiation dose allows time for normal cells to repair themselves between treatments, thereby reducing side effects. Fractions are usually given five days a week with a rest over the weekend. Therapy sessions often take less than an hour.

The radiation beams are generated by a machine called a linear accelerator. The beams are precisely shaped to match the tumour and are aimed from a variety of directions by rotating the machine around the patient.

Gamma knife radiosurgery

The Gamma Knife is not a knife in the conventional sense, but uses a focused array of intersecting radiotherapy beams to treat lesions within the brain.

Within the central body of the Gamma Knife there is an array of separate sources and each of these produces a fine radiation beams. The sources are evenly distributed over the surface of the source core so that each beam is directed at a common focal spot – the tumour.

The resultant intensity of radiation at the focus is extremely high whilst the intensity only a short distance from the focus is very low. This enables a high dose of radiation to be delivered to the abnormal tissues whilst sparing the adjacent healthy brain tissue.  Gamma knife treatment usually requires only a single treatment.

Cyber knife

The CyberKnife has X-ray cameras that monitor the position of the tumour and sensors that monitor the patient’s breathing. This enables a robotic arm to reposition the radiotherapy beam during treatment in order to minimise damage to healthy tissue. CyberKnife moves with the patient’s breathing and can track a moving tumour. It is not necessary to fix the head of the patient in a frame, as is required for Gamma knife treatment.

Because of its accuracy, CyberKnife allows larger fractions (doses) of radiotherapy to be delivered, meaning that the patient requires fewer hospital visits. Cyber knife treatment usually requires three treatments.