PRIMARY BRAIN TUMOURS

TUMOURS DESCRIBED BY CELL TYPE OR TISSUE

Like all types of tumours, brain tumours arise from a single cell with damaged DNA called a mutation that leads to uncontrollable cell replication. It leads to the cell cloning itself rapidly into billions of copies that eventually leads to a mass called the tumour. While there are rare genetic causes for brain tumours that run-in families and there are some risk factors such as exposure to ionising radiation the majority of people that are diagnosed with a brain tumour have no obvious cause – in essence, it is bad luck.

Brain tumours are given a grade after the pathologist has examined them – see above. This grade is called the World Health Organisation (WHO) grade. The grade ranges from 1 to 4, with 1 being a very good grade that means a tumour is potentially curable and 4 being a very bad grade that means the tumour tends to spread aggressively. The higher the grade, the more difficult it is to treat the tumour.

In order to understand the different types of brain tumours, it is best to understand the normal cells or tissues that brain tumours arise from.

Astrocyte – There are more than 1 trillion astrocytes in the brain. Their main function is to support the nerve cells in the brain. The majority of brain tumours arise from astrocytes – however, there are many different types of brain tumours arising from these cells.

• Diffuse Astrocytoma – This tumour tends to arise in young adults and commonly presents with a seizure. It is a Grade II, low-grade tumour that unfortunately has the potential to change into more aggressive forms. They are characteristically associated with a mutation in the IDH gene. Maximal removal of these tumours is very important as it significantly increases the odds of long-term survival.
• Anaplastic Astrocytoma/Glioblastoma – Both of these tumours are high-grade tumours with anaplastic astrocytoma being a Grade III tumour and Glioblastoma being a grade IV tumour. These tumours tend to be aggressive and spread widely. Maximal tumour removal, age and patient independence are the factors that have been shown to improve survival
• Pilocytic Astrocytoma – This is a Grade I brain tumour that is more common in children and tends to occur more frequently in a part of the brain called the cerebellum. However, it can arise in any location. Complete removal of this tumour is associated with cure.

Oligodendrocyte – These cells wrap around the nerve cell axons and insulate them in a way that resembles plastic around a copper wire. By insulating the axons, electrical impulses are carried efficiently from one nerve cell to the next without leakage of current.

• Oligodendroglioma – This tumour is relatively infrequent and can be graded as either Grade 2 or 3. The characteristic genetic hallmark is shifting of DNA from one chromosome to another – this is called 1p/19q co-deletion. They tend to respond well to complete surgical resection.

Arachnoid Cap Cells – These cells are generally located on the surface of the brain and involved in creating a thick membrane that surrounds the brain as well as helping drain the brains water system into the big veins of the brain.

• Meningioma – This tumour is the most common benign type of brain tumour with more than 80% of meningiomas being grade 1. For the most part, they arise from the surface membrane that protects and surrounds the brain called the dura. There are many different subtypes of this tumour, and it can generally be located anywhere within the skull cavity. Complete removal of this tumour is very often curative.

Ependymal cells – These cells line the inner surface of fluid-filled cavities within the brain called ventricles. Ventricles are responsible for creating brain fluid called cerebrospinal fluid (CSF). Ependymal cells form a barrier between the brain and the CSF and also provide a filtering system.

• Ependymoma – there are many different types of ependymoma that can range from Grade II to III. These tumours are more common in children, but they can also arise in adults. Their location also tends to be different depending on the age of the patient. Surgery with the aim of complete resection is the best treatment as it has the potential to achieve long term survival.

Schwann Cell – These cells are only slightly different from the oligodendrocytes described above. The brain has nerves that are bundles of wires called axons whose role it is to transmit information between the brain to a target tissue such as to muscles to move the face or from the organ that perceives sounds to create hearing etc. The Schwann cells wrap around the axons within the nerves in order to provide insulation and prevent the leakage of current and bad transmission of information; much like the plastic around a copper wire.

• Vestibular Schwannoma – is, for the most part, a tumour of the Schwann Cells arising from the 8th cranial nerve. This nerve is responsible for hearing and balance. Patients usually present with hearing problems and balance problems. The tumour is associated with Neurofibromatosis type II, but most patients with this tumour do not have this syndrome. Management decisions pertaining to this tumour can be quite intricate and are dependent on many factors such as the size of the tumour, patient age, ability to hear and presence of a neurofibromatosis type 2.

External Granule Cell – This cell is found closely compacted with similar cells within a layer in the cerebellum. This cell is responsible for integrating information within the cerebellum for the purpose of coordination of our limbs and speech.

• Medulloblastoma – this brain tumour is common in children and usually arises within the middle of the cerebellum, which is the lower part of the brain situated at the back of our heads near our neck. Children usually present with balance problems and gradual symptoms; however, they can also present as acutely unwell with headaches and vomiting. Maximal removal of the tumour is very important for long term survival.

Vascular Tissue – Like all organs, the brain requires the constant supply of blood – in fact, 20% of the blood circulating every minute goes to the brain. In order for blood to reach the brain in travels in blood vessels – these blood vessels are known as vascular tissue

• Haemangioblastoma – this is a tumour that arises from abnormal blood vessels. They are benign tumours with a very rich blood supply that grows over time to cause symptoms by pressing the brain. They can behave fluidly in them like a cyst, or they can be solid. Sometimes these tumours can be associated with the Von Hippel Lindau syndrome. Complete surgical removal can be curative

Rathke's Pouch – This is an embryological remnant, which means that this tissue is not normally present in adults. The tissue appears for a very short while when we are developing as embryos. It is responsible for forming and attaching the pituitary gland to the brain

• Craniopharyngioma – this is a tumour that arises from Rathke's pouch. It can present in both children and adults. It can be a cyst, or it can be solid. It is close to the nerves for vision, so as it grows, it can cause blindness. It can also cause weight gain and sleep disturbance. There is a range of treatments for craniopharyngioma with the exact anatomy of the tumour dictating whether surgery can be successful.

TUMOURS DESCRIBED BY LOCATION

The brain is composed of many unique regions with different functions. Some regions can be tricky areas to operate within and require advanced anatomical knowledge. The regions are described separately here as they tend to have tumours that arise from many different types of cells.

• Pituitary Tumours
  The pituitary gland is in a very central part of the brain and is in an area situated behind our eyes and nose. It is very small but is very important as it secretes the hormones that control the entire bodies regulatory functions. Tumours in the pituitary gland can present with pain behind the eyes, deterioration in vision or as a syndrome from the overproduction of hormones. The common syndromes as a result of this overproduction are Cushing's syndrome and acromegaly; however, there are rarer ones. Surgery is an excellent treatment for these pituitary tumours – especially with the modern endoscopic techniques.
• Brainstem Tumours
  The Brainstem connects the brain with the spinal cord and is the major highway for information that passes between the brain and spinal cord and vice versa.
• Ventricular Tumours
  The Ventricle is fluid-filled cavities that are deep within the brain. There function to create about 500mls of fluid called CSF every day. There is a range of different types of tumours that can arise from this area such as colloid cyst, choroid plexus papilloma and central neurocytoma. Depending on the tumours grade, removal of these tumours can be curative.
• Pineal Region Tumours
  The pineal region is located deep in the brain on the back of the upper brainstem between the cerebrum and cerebellum. This area is surrounded by many important structures, including veins that drain the inner part of the brain. Patients commonly present with problems in the movement of their eyes and blurry vision. There is a huge variety of different tumours that arise from this region, which includes pineocytoma, pineoblastoma, and embryonic tumours. The prognosis, surgical goals and need for radiotherapy is highly dependent on the final diagnosis.
• Clivus – Chordoma and Chondrosarcoma
  The clivus is a bony part at the base of the skull where the skull joins the cervical spine. Tumours in this area are deep-seated and are generally either chordoma or chondrosarcoma. This is a deep site and requires advanced endoscopic techniques to achieve tumour removal. For the most part, Gross total resection achieves good long terms of survival.
• Spinal Cord Tumours
  The spinal cord, like the brain, is also susceptible to tumours; however, tumours in the spinal cord, are much less common. Although uncommon, the tumours that do arise in the spinal cord tend to be astrocytoma, ependymoma, meningioma and neurofibroma. Tumours tend to present with changes in sensation of the limbs, weakness in the limbs or problems with maintaining control of the bowel or bladder. Depending on the type of tumour, surgery can potentially be curative.
• Orbital Tumours
  The orbit is the eye socket – i.e. the bones that surround the eye. Although rare, tumours can arise in this region and push the eyeball and the muscles of the eye. Patients can present with visual problems, double vision or gradual protrusion of the eye outwards. There are many different types of tumours that can arise from the orbit with a very wide spectrum of behaviour. Surgical removal of orbital tumours should be the goal, and in some cases, depending on the diagnosis, removal can achieve cure.

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