CONDITIONS TREATED

Skull base surgery (particularly acoustic neuromas)

The term skull base surgery refers to the special surgical skills and techniques which are necessary to gain access to the deepest reaches of the brain. Skull base surgery is very challenging for the neurosurgeon and is, generally speaking, an area in which only some specialist surgeons work. It requires a highly specialised and detailed grasp of the complex anatomy of the area as well as considerable expertise. In view of the difficulty of the approach and the need to avoid damage to delicate and vital areas, skull base operations can be very lengthy. An anaesthetist with experience in this branch of work is an essential part of the team. Because of the proximity of the face and neck to the skull base, the neurosurgeon will often work alongside an ear, nose and throat, maxillo-facial or plastic surgeon when performing these operations.

The area around the skull base can be affected by a number of different conditions, including congenital malformations, trauma, aneurysms and tumours. Tumours that may be present in this area include:

Meningiomas

Meningiomas arise from the cells of the meninges (the covering of the brain and spinal cord). They are almost always benign and usually grow very slowly. They can exist for several years and reach quite a considerable size before they begin to cause symptoms and are detected. Meningiomas are most commonly found in middle-aged patients, with women twice as likely to suffer than men.

The symptoms of meningioma vary according to their location and size, but headache, seizures (fits) and visual problems are often seen.

Diagnosis can be confirmed using CT or MRI scans and angiograms are sometimes performed to investigate the tumour's blood supply.

Surgery is nearly always the treatment of choice for meningioma. Because the tumour stems from the meninges rather than the brain itself, complete removal is often possible, though this does not always prevent regrowth which is, however, uncommon.

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Vestibular schwannomas

A vestibular schwannoma is a benign tumour of the VIIIth (vestibulocochlear) cranial nerve which leads from the brain to the inner ear in an area known as the cerebellopontine angle. The vestibulocochlear nerve (as its name suggests) is actually two separate nerves, the cochlear nerve (responsible for hearing) and the vestibular nerve (responsible for balance). These nerves pass from the inner ear to the brainstem through a narrow bony tube about 2 cm long called the internal auditory canal. Also running through the internal auditory canal is the facial nerve (VIIth cranial nerve). It is in this area that vestibular schwannomas originate from an overproduction of the Schwann cells which form an insulating sheath around the nerves.

Although they are benign, these tumours are located in an awkward spot, close to many important neurological structures.

Nowadays, the vast majority of vestibular schwannomas are diagnosed at a relatively early stage. Patients who present to their GPs with unexplained, unilateral hearing loss will generally be referred to an ENT (Ear, Nose and Throat) specialist who will perform some special hearing tests and arrange an MRI scan. If a vestibular schwannoma is detected, a neurosurgeon will become involved who will handle the case jointly with an ENT surgeon who is an expert in this field.

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Glomus jugulare tumours

Glomus jugulare tumours are very rare, benign tumours which occur in the temporal bone at the base of the skull. Because of their proximity to the cranial nerves, they can cause hearing loss, difficulty in swallowing and tinnitus.

Because of their location, glomus jugulare tumours require highly specialised surgical techniques. This frequently involves both a neurosurgeon and a head and neck surgeon. Sometimes, the tumour will be embolised prior to surgery to reduce its blood supply. Surgery may be followed by radiotherapy to reduce the chance of recurrence.

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Craniopharyngiomas

These are tumours that develop in the region of the pituitary gland, near the hypothalamus. They occur in childhood and adolescence and also in patients over the age of 50. Craniopharyngiomas can grow quite large (up to 3cm) before they begin to impinge on surrounding structures, causing symptoms that lead to a diagnosis. Although traditionally classified as benign, craniopharyngiomas can have devastating effects, producing visual difficulties and problems with growth.

The goal of surgery in the treatment of craniopharyngiomas is to remove as much of the tumour as possible while preserving brain, pituitary and visual function. Radiotherapy, either conventional or stereotactic, is then often given.

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Pituitary tumours

Tumours of the pituitary gland (pituitary adenomas) are always benign. They are relatively common, making up about 10% of all primary brain tumours. They are most commonly found in young or middle aged adults. The tumours can be non-secreting or secreting, meaning that they secrete excess amounts of one of the pituitary gland's hormones.

Symptoms of pituitary adenoma can arise from direct pressure on surrounding tissue or, in the case of secreting tumours, be related to excess hormone production. The specific symptoms will depend on which hormone is involved. Where too much prolactin is being produced, women may experience cessation of menstruation and galactorrhoea, and men impotence or infertility. Where growth hormone is being produced, gigantism can occur in adolescents or acromegaly in adults. Excess secretion of adrenocorticotrophic hormone (ACTH) may induce Cushing's syndrome, a complex of symptoms which includes a moon shaped face, weight gain, increased facial hair in women and depression.

Pituitary adenomas are often discovered during blood tests to investigate symptoms such as those above. A CT or MRI scan will confirm the diagnosis. Pressure on the optic nerve can be detected by an eye test where visual field defects (classically, hemianopia) will be detected.

Surgery is the most effective treatment for pituitary adenoma. This is usually done by approaching the gland through the nose or under the upper lip (transphenoidal surgery). The aim of surgery is to remove the tumour whilst leaving as much as possible of the pituitary gland intact. Radiotherapy may be used after surgery.

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Chordomas

Chordomas develop from remnants of notochord, the flexible spine-like structure that forms and dissolves early in foetal development and is later replaced by the spinal cord. They occur both in the lower spinal cord and at the base of the skull.

Chordomas grow slowly and can reach a considerable size before any symptoms are noticed. The most frequent presenting symptoms are headache and visual problems. Diagnosis is normally by CT or MRI scan.

Because chordomas affect the bone of the skull base, complete surgical removal can be difficult and regrowth often occurs.

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How do surgeons get to the skull base?

The skull base is extremely difficult to reach, so surgeons have devised a number of different routes to try and reach their target with as little damage to other structures as possible. Some of these are:

  • transorbital - through the roof of the orbit (eye socket)
  • transfrontal - the frontal bone
  • transphenoidal - through the sphenoid sinus
  • transtemporal - through the temporal bone at the side of the head
  • pterional
  • transoral - through the back of the mouth
  • translabyrinthine - through the inner ear
  • sub-occipital retrosigmoid - through the occipital bone behind the ear
  • transethmoid - through the ethmoid sinus at the side of the nose

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