Skull base tumours

These are non-cancerous growths affecting the nerves of balance (vestibular nerves) which usually come to light as a result of hearing loss on the affected side, often coupled with ringing/whistling noise on that side (tinnitus) and disturbance of balance. These tumours are usually slowly growing (1-2mm per year) and this means there is no urgency to treat after diagnosis.

In the UK, it is often recommended that there should be a period of observation with scans at intervals to ensure the tumour is growing before recommending treatment. This is particularly the case if the vestibular schwannoma is small on initial scans. Currently, the commonest treatment is radiosurgery, often using the Gamma Knife, but for large tumours (over 3cm in diameter), surgery is probably a better option. Treatment aims to prevent further clinical deterioration, as once hearing is lost it cannot be restored by any intervention, and tinnitus is also resistant to therapy.

The pituitary gland is a small, but important structure in the base of the skull, below the optic nerves and just deep to the top of the nose. It is responsible for driving many of the hormones needed by the body such as thyroxine, cortisone, growth hormone and the ‘sex’ hormones. Tumours are not uncommon in this gland, some produce an excess of hormones and lead to diseases such as Cushing’s (excess steroid), acromegaly (excess growth hormone) or infertility (excess prolactin).

Others do not produce hormones but as they grow they damage the normal pituitary gland and can also compress the optic nerves leading to visual failure. These tumours are almost never cancerous, and usually are slowly growing. The need for treatment depends on their size and their effects. One group of tumours (prolactin secreting) can be treated with medication without the need for surgery.

The other types of tumour usually need an operation which is now generally performed using minimally invasive techniques through the nose. Surgery is not always curative and there may be a need for radiation treatment as well, in addition to medication to replace any hormone deficiency arising from tumour growth or surgery.

Although pathologically distinct, these tumours are often linked together as until relatively recently it was difficult to distinguish between them, either on scans or even by a pathologist looking at surgical specimens. They arise at the base of the skull, generally in front (or slightly to the side) of the brainstem. Chordomas arise in part of the skull known as the clivus (but can also arise in the spine), and chondrosarcomas in the part called the petrous.

They may reach a large size before causing any symptoms, but may lead to double vision due to pressure on one of the nerves responsible for eye movements. Headache is another common, but non-specific symptom. These are low grade cancers which normally grow slowly. Treatment generally consists of surgery to confirm a diagnosis and to remove as much of the bulk as possible, followed by radiation treatment which may involve proton beam therapy or standard radiosurgery with Gamma Knife.

These are tumours arising just above the pituitary gland at the base of the skull. They arise from cells remaining from the time of development in the womb (pituitary gland embryonic tissue). As they are not in their normal position, the cells grow and divide forming a non-cancerous mass which can give rise to a number of symptoms. They are generally discovered in childhood but can present much later in adult life. They cause effects by pressure on the pituitary gland (hormone deficiencies), pressure on the optic nerves (visual loss) or pressure on the part of the brain called the hypothalamus. The hypothalamus helps to regulate appetite, body temperature, sleep patterns, memory, alertness and emotional responses.

Early puberty is a common problem in children with these tumours; in adults it tends to be visual disturbance or somnolence. Although not cancers, these tumours can be difficult to treat due to their location and the risks of damage to vision and to the hypothalamus from surgery. Generally, a combination of surgery and radiation treatment is used but in adults newer targeted drug treatments are also being trialled (BRAF inhibitors, which have shown some promise in selected patients with appropriate tumours.

Meningiomas are almost always non-cancerous tumours, arising from the coverings of the brain (membranes known as the meninges). When they occur on the surface of the brain, they are normally easily removed and cured by surgery. Some of these tumours, however, arise in areas surrounded by nerves, arteries and veins which increases the risk that surgery will cause additional problems for the affected individual, and also reduces the chance that all of the tumour will be removed with a corresponding increased chance of recurrence in the future. Tumours arising around the base of the skull generally fall into this ‘difficult’ category.

Treatment is not always needed as growth of these tumours may stop (particularly in women after the menopause), or may be so slow as not to require any intervention during an individual’s life. For those patients with growing tumours, which are causing clinical problems, treatment is often recommended and this may be surgical, radiosurgical (Gamma Knife) or a combination of both. There are currently no drug treatments which are reliably effective in the treatment of meningiomas.