A brain tumor is an abnormal growth in the brain, causing compression and loss of important functions. The brain resides inside the cranial cavity. It is different from other organs since it has an external exoskeleton in the form of the skull to protect it. Although the lungs and heart also have a chest wall for protection, it is not as rigid as the skull. The skull protects the brain from outside trauma and provides an optimal environment for its function. However, the volume inside the skull cannot change.
Another different feature of the brain is tightly regulated pressure. Cerebro-spinal production and absorption is the main mechanism maintaining the pressure in the normal range. Any deviation from this pressure causes pain and functional disturbance.
A growing tumor has to come at the expense of losing the volume of other components in the skull. Therefore, the brain tissue, cerebrospinal fluid, and blood in brain circulation have to retract to make extra room for growing tumors. This process is called compensation, and usually, at this stage, the pressure is not elevated. However, once compensation mechanisms have been exhausted, the pressure rises.
Another specific aspect of the brain is the lack of pain receptors. On the other hand, dura mater (a brain cover) has numerous pain receptors. Therefore, headaches originate not from the brain but from the dura. Brain compression by the tumor does not cause pain. Pain is caused either by elevated pressure compressing the dura or when the dura is directly affected by a tumor.
There are several categories used to classify brain tumors.
Primary - originating from the brain.
Metastatic – spreading to the brain from other places.
Supratentorial - located above the tentorium; further subdivided into specific areas of origin - frontal, temporal, parietal, occipital, insular, thalamic, ventricular, etc.
Infratentorial - located below the tentorium: usually in/around the cerebellum, brainstem, and fourth ventricle.
Skull base - located below the brain at the base of the skull.
Superficial - located close to or in the brain's outer surface.
Deep - located in deep, hard-to-reach areas of the brain.
World Health Organization (WHO) classification is the most updated and commonly used system for pathological classification of brain tumors. Common brain tumor types are astrocytoma, oligodendroglioma, ependymoma, glioblastoma multiforme, meningioma, craniopharyngioma, schwannoma, etc.
According to the WHO classification, there are four grades of malignancy (I-IV) for primary brain tumors. Grade I is the most benign, and IV is the most malignant type. It is well known that the grade of the tumor is the most important factor affecting the outcome of treatment.
Brain tumors may present with a variety of symptoms depending on location, size, and growth rate. Benign tumors are usually slowly growing and allow the brain to adapt to the compressive effect. They may reach very large sizes before producing any symptoms. Malignant brain tumors, on the other hand, grow aggressively and tend to cause edema in surrounding tissue. Yet even malignant tumors do not cause symptoms before reaching a particular size.
Symptoms of brain tumors are divided into two groups
General - All tumor types can cause these symptoms. The symptoms are due to increased pressure in the brain. Headache, nausea, vomiting, blurred vision, and sleepiness are frequently encountered symptoms.
Local - symptoms due to local effects on a specific area. Weakness in arms and legs, numbness, visual disturbances, seizures, dizziness, vertigo, hearing impairment, and many other symptoms are due to the local effect of the tumor.
Imaging of the brain is an essential step in evaluating brain tumors. MRI with the gadolinium contrast is the best modality to show the tumor and its relation with the surrounding brain. In the majority of cases, the MRI can provide information about the nature of the tumor. In difficult cases, special MRI modalities like functional MRI, diffusion tensor imaging, and MR spectroscopy can provide invaluable details. In some cases, a CT scan can be preferred if bone structures need to be visualized. In some cases, laboratory tests are required for detailed diagnosis. For example, pituitary adenoma evaluation involves blood hormone levels.
Pathological analysis of the tissue is the most important aspect of the diagnosis. No test can be as reliable as an examination of the tumor. For that reason, obtaining tissue samples and subsequent analysis is the cornerstone of brain tumor management.
Tags: Brain tumor symptoms, brain tumor diagnosis, brain tumor types, brain tumor classification
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