Brain Tumour - Towards More Accurate Diagnosis
Brain tumour is one of the most devastating forms of human disease. The mystery and aura of the brain often brings about great anxiety to the layman. Sadly, brain tumours are the second most common form of malignancy in children and the sixth to eighth most common form of malignancy in adults.
Brain tumours are conventionally classified into primary tumours, which originate in the brain and secondary (or metastatic) brain tumours, which originate from a different site such as the lung, breast or colon.
Primary tumours of the brain and spine account for less than 2% of malignancies but are responsible for 7% of the years lost of life lost from cancer prior to 70 years of age. In childhood, these figures are even more dramatic and primary brain tumours account for 20% of malignant tumours diagnosed before 15 years of age.
Gliomas are the most common primary brain tumours, and arise from the cells in the brain known as glia cells, (hence the term glioma). Glia cells are composed of various different cell types such as astrocytes, ependymal cells and oligodendrocytes, and tumours of these cell types are called respectively astrocytoma, ependymoma and oligodendroglioma.
Most people are familiar with the staging of cancers which gives an indication of how bad the cancer is based on tumour size and spread.
Neurosurgeons are often asked by their patients and families about the stage of the brain tumour. A unique distinguishing characteristic of brain tumours is that the tumours very rarely spread out of the confines of the brain, and as such, a grading rather than a staging system is used. This is based on the appearance of malignancy of the tumour under a high-magnification microscope: Tumours with high grading are more aggressive, destructive and harder to treat. Even without distant spread of the brain cancer, the localised invasion of the tumour into the surrounding brain and the pressure effects of the expanding tumour can lead to severe brain damage, complications and death.
Another interesting fact about brain tumours, particularly gliomas, is the fairly frequent presence of tumours of different grade within a single brain tumour mass. Furthermore, the highest tumour grade present in the mass will determine the behaviour and survival outcomes. Hence, even if only a very small proportion of the tumour is of a high grade, this proportion of the tumour will have to be dealt with. This has obvious implications in the accurate diagnosis and appropriate treatment of brain tumours. Treatment such as radiation therapy and chemotherapy are not without risk and side effects, and this means that treatment should only be administered with accurate diagnosis and grading of a brain cancer. Confirmation of a brain tumour usually requires surgical removal of tumour tissue for examination. Sampling error (error resulting from the chance removal of tumour of lower grade even when there is high grade MRI scan showing a few discrete tumours located deep within critical brain structures (region 1 is investigated further on MR spectroscopy) tumour present) must be minimised to provide accurate diagnosis and start proper treatment. Extensive surgical removal of the brain tumour is therefore often recommended to reduce this sampling error.
Regrettably, brain tumours may often be small and located in deep structures of the brain and this sometimes make extensive surgery risky. In such situations, a needle biopsy is recommended and involves the very accurate placement of a small needle with the aid of sophisticated computer software into the tumour to obtain a small amount of tissue for examination. This procedure carries a low surgical risk but the inherent problem of sampling error in view of the small amount of tissue obtained needs to be addressed. A technique to target specific regions with the most aggressive tumour of the highest grade will certainly aid with the diagnostic process. Magnetic resonance spectroscopy (MRS) is a technique which allows for the non-invasive pre-surgical identification and measurement of specific chemicals within the brain. Different chemicals can be detected and measured over specific small areas of the tumour.
Cancerous regions have certain characteristics with the most well-described finding of higher levels of a substance known as choline. Finding and targeting the choline-rich areas will improve the chances of obtaining and staging the more cancerous cells and reduce the possibility that a falsely low grade of tumour will be wrongly diagnosed. We have recently identified and published our findings that besides choline, lipids (or fatty acids) may potentially be a more important chemical to consider, and may also be useful to identify the highest grade of tumour, together with choline.1 We hope that this new research finding can contribute to greater diagnostic accuracy, greater yield and result in the most appropriate treatment for our patients.
References
- Targeting regions with highest lipid content on MR Spectroscopy may improve diagnostic yield in stereotactic biopsy (Wai Hoe Ng, Tchoyoson Lim) Journal of Clinical Neuroscience (2008) 15(5): 502-506.