Brain tumours including skull base tumours

A tumour is an abnormal growth of cells. Cells are the body’s basic building blocks – they make up tissues and organs. The body constantly makes new cells to help us grow, replace worn-out tissue and heal injuries.

Normally, cells multiply and die in an orderly way, so that each new cell replaces one lost. Sometimes, however, cells become abnormal and keep growing. In solid cancers, such as brain cancer, the abnormal cells form a mass or lump called a tumour.

Brain tumours are divided into primary and secondary tumours. Primary tumour means arising from cells in the brain itself. These tumours rarely spread to other parts of the body, but can spread to other parts of the brain and spine. There are more than 40 types of primary brain and spinal cord tumours. (also known as central nervous system [CNS} tumours).

The classification of primary brain tumours is revised every few years but a panel of world experts. A tumour is defined a certain type based on the type of tumour cells seen under the microscope after the pathologist has processed the brain tumour tissue. Increasingly specific genetic tests, that determine how a cell is likely to behave are also helping to determine tumour classification.

Secondary tumours refer to cancers that start in other parts of the body and then travel to the brain. Most of the time they get to the brain as small clusters of cells that break off and travel in the blood vessels to the brain. They can sometimes reach the brain from direct spread from structures adjacent to the brain. Another name for a secondary cancer is a metastasis. A metastasis keeps the name of the original cancer. For example, lung cancer that has spread to the brain is known as metastatic lung cancer.  

Primary brain tumours can either be benign or malignant. A slow growing tumour that is unlikely to grow back quickly after treatment is called benign. Some tumours are slow growing and are termed low grade. This can be confusing as these are not benign tumours. These tumours have the potential to convert to high grade malignant tumours. 

Even brain tumours that are benign can sometimes be life threatening because of where they grow. They grow slowly but gradually compress really important structures in the brain, and cannot be easily removed without causing severe side effects.  

Primary malignant brain tumours are brain cancers. These are aggressive life-threatening tumours that grow rapidly and cause significant destruction of normal brain areas. They can reoccur in the same area even after aggressive treatment and sometime will spread to other parts of the central nervous system. 

Brain tumours can occur in any part of the brain. Sometimes they grow quickly and sometimes they develop over many years. This means that the number of possible symptoms that a patient with a brain tumour might experience are almost impossible to list completely.  

Some of the more common presentations can include headaches, seizures, focal neurological problems such as weakness or speech abnormalities. Sometimes brain tumours will cause diffused increase in pressure in the skull. This can result in headaches, nausea and vomiting and drowsiness.  

While patients with brain tumours may experience headaches, over the years I have seen a large number of patients who have tumours but never had any headaches. Please do not ignore other symptoms just because you do not have headaches. Typically concerning headaches are worse first thing in the morning and not easily relieved by simple medication such as Panadol. Any new or persistent headache should be investigated. 

An adult who has never had a seizure before and experiences a seizure should always have a brain scan to make sure there is no mass in the brain to account for the new onset of seizure. The same holds for patients with epilepsy that had previously been well controlled and now present with a new unprovoked seizure.  

Brain tumours are often first diagnosed with a CT scan of the brain, ideally with the addition of intravenous contrast (dye). This will provide initial basic information, and a carefully conducted and reported study is unlikely to miss a brain tumour if it is present.  

Nevertheless, an MRI (magnetic resonance imaging) study will provide greater detail of the brain and any abnormality that is present. Most patients who are suspected to have a brain tumour are likely to undergo an MRI at some point prior to treatment. In some cases, additional tests may be required to better define the abnormality. Your specialist will determine if you need any further tests,  

If the above tests indicate that you have a likely brain tumour, you will require a specialist opinion from a neurosurgeon. Not everyone who is diagnosed with a brain tumour will require surgery, but it is important to get an opinion on how to best manage this diagnosis. 

In some cases, the exact nature of the mass may not be certain and then a cautious approach of observation is best. Some benign tumours are found by chance when tests are done for other reasons. These tumours are usually also observed, at least initially. 

When your specialists feels that surgery is required this may be to remove the tumour, but it may be that a biopsy of the tumour is advised. All tumours and all patients are different and individualised tailor-made treatment is best.  

Treatment of brain tumours often requires a multidisciplinary team approach. The members of the team will vary depending on the type of tumour. In general treatment options for brain tumours include surgery, chemotherapy ( medication) and radiotherapy.

Skull base tumours 

At the base of the skull there is a high concentration of really important blood vessels and nerve. The blood vessels are called the circle of Willis by anatomists. This blood vessel system if formed by the two carotid arteries in the front and the two vertebral ateries at the back. The carotid arteries travel from your neck through specialised pathways in the skull to your brain. 

The vessels from the right and the left side communicate with each other to allow blood from one side to potentially be able to supply the brain on the opposite side of the brain if the need arises.  

The nerves at the skull base are called the cranial nerves. They travel directly from the brain through specialised bony channels in the skull to structures in the face, head and neck.  

While tumour that arise at the base of the skull are more often than not benign, they are intimately associated with these important structures described above. This makes treatment of the tumours particularly challenging and sometimes means that even though they are benign they cannot be treated adequately and safely with surgery.  

 

Some tumours in the middle of the skull base, such as pituitary tumours are in a unique position that allows them to be accessed via the nose. These surgeries are usually performed by a team of surgeons comprising of an ear nose and throat (ENT) surgeon and a neurosurgeon.

An endoscope (specialised camera) is used to navigate the cavities deep in the nose that then lead straight to the bone covering the base of the skull in the midline. This bone can then be carefully drilled away with a specialised drill. Tumours in the region can then be treated without having to manipulate the surrounding brain.

This means that no visible scar on your head, despite having had a brain operation. Recovery from these surgeries can at times be quicker than for patients who have to have a a craniotomy. 

While this appears to be a less invasive option, it still has significant risks and still remains a major brain operation. Not all tumours can be operated from this approach and your specialist will be able to tell you if this is a feasible option for you. 

Image source: Sellar and Parasellar Tumors, Diagnosis, Treatments and Outcomes, Edward R. Laws Jr. & Jason P. Sheehan, 2012