Brain tumours are tumours of the central nervous system (CNS). They originate in brain tissue or the surrounding intracranial or spinal structures. It is also possible for other cancers (e.g. lung, breast, skin and bowel cancers) to metastasise to the brain.
Distribution of surgically treated brain tumours:
- 50% are gliomas (brain tumours that arise from glial cells)
- 25% are meningiomas (brain tumours that arise from the membranes surrounding the brain)
- 10% are schwannomas (tumours of the nerve sheath)
- 10% are hypophyseal adenomas (pituitary tumours)
- 5% are other tumours.
Meningiomas (meningeal tumours)
90% of meningiomas are benign (Grade I) and rarely recur after total removal. Meningiomas arise from arachnoid cells and are usually attached to the dura. They are located inside the skull or in the spinal canal and are typically single, well-circumscribed and slow-growing tumours which tend to push brain tissue aside as they grow. Usually, symptoms only occur when the size or location of the tumour causes it to compress nerves or blood vessels.
Gliomas (brain tumours)
Gliomas arise from glial cells which form the supportive tissue of the brain. There are four main types of glioma - astrocytoma, oligodendroglioma, mixed glioma (also called oligoastrocytoma) and ependymoma. Tumours are graded from benign (Grade I) to malignant (Grade IV). Currently, only Grade I gliomas can be cured by surgical removal. For Grade II to IV gliomas, surgical procedures are applied to prevent or slow down the growth of the tumour. In addition to surgery, radiation therapy and chemotherapy are required for the treatment of Grade III and IV tumours, in particular. Unlike meningiomas, gliomas are diffuse, which prevents complete excision.
Metastases
Metastatic or secondary brain tumours are the most common intracranial tumours, representing over 50% of all tumours in the central nervous system. The most common cancers metastasising to the brain include lung, breast, colon and kidney cancers and melanomas.
Brain metastases are found in about one in every four cancer patients. 80% of the metastases occur in the cerebrum and 20% in the cerebellum. In patients with secondary (metastasised) brain cancer, 40% have a single secondary tumour while 60% have several metastases.
Secondary brain tumours are surgically removed only when the primary cancer is under control and there is only a single brain metastasis. In case of aggressive cancer or several brain metastases, surgery is of little use. Radiation therapy may offer an alternative to surgery. Patient may receive conventional radiotherapy or targeted radiotherapy (stereotactic radiotherapy), where the irradiation beam is targeted very accurately at a small area. The prognosis of a brain metastasis depends on the stage and prognosis of the primary cancer.
Pituitary adenomas (Hypophyseal tumours)
Pituitary tumours are almost always benign. However, they may cause hormonal disturbances (excessive or insufficient hormone production) or a large pituitary tumour may compress the optical nerves and cause disturbances in vision and even blindness. Neurosurgeons collaborate with endocrinologists to treat pituitary tumours. Surgery is indicated in patients whose tumour cannot be treated with specific drugs. Transsphenoidal surgery performed through nose with the use of endoscope is nowadays the treatment of choice. Extensive pre- and postoperative examinations are required to monitor hormonal secretion and any abnormalities are addressed, if necessary.
Acoustic neuromas (vestibular schwannomas)
Acoustic neuromas are benign tumours which grow on the epineurium of the eighth cranial nerve (vestibulocochlear nerve). These well-circumscribed tumours grow slowly and are regularly monitored and treated with surgery or targeted radiotherapy, depending on the size and growth pattern of the tumour.
Acoustic neuromas typically arise from the vestibular division of the nerve which control balance while the cochlear division controlling hearing functions normally. As a result of this, hearing can be preserved in over half of patients with a small tumour and normal hearing. However, if the tumour is large or the patient already suffers from hearing loss, the hearing is likely to be affected by surgery.
Another significant risk of acoustic neuroma surgery is transient or even permanent facial nerve dysfunction which may cause facial palsy. The acoustic nerve is very close to the facial nerve. Therefore, the facial nerve may be damaged when an acoustic neuroma is surgically removed. With modern microneurosurgical techniques, permanent facial nerve palsy is very rare (less than 5%).
Spinal cord tumours
Nearly every fifth CNS tumour is located in the spinal cord. The most common spinal cord tumours include intramedullary gliomas and ependymomas and extramedullary meningiomas and schwannomas. Furthermore, other cancers may metastasise to the spine or spinal canal.
Treatment depends on the type of the tumour. Microneurosurgery is often applied to treat extramedullary tumours (meningiomas and schwannomas) and the results are usually good. The treatment of intramedullary tumours presents a greater challenge and each case must be evaluated individually. Some tumours can be treated surgically while others cannot. Surgery is hardly ever used in the treatment of metastases in spinal cord. These are typically treated using radiation therapy.