BRAIN TUMORS

 

Definition

Brain tumor is an abnormal growth in the brain causing compression and loss of important functions.

Anatomy

Brain resides inside the cranial cavity. It is different from other organs since it has external exoskeleton in form of the skull to protect it. Although lungs and heart also have chest wall for protection it is not as rigid as the skull. Skull protects the brain from outside trauma and provides optimal environment for its function. However the volume inside the skull cannot change.

 

brain inside transparent skull

 

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 expense of loosing 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 tumor. This process is called compensation and usually at this stage the pressure is not elevated. However once compensation mechanisms have exhausted the pressure raises. 

 

Schematic illustration of a brain tumor

 

Another specific aspect of the brain is lack of pain receptors. On the other hand dura mater (a brain cover) has numerous pain receptors. Therefore, headache 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 tumor. 

Classification

There are several categories used to classify brain tumors. 

Origin

Primary - originating from the brain.

Metastatic – spreading to the brain from other places.

Location

Supratentorial - located above the tentorium; further subdived 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 or in the brain outer surface.

Deep - located in deep, hard-to-reach areas of the brain.

Type

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, epandimoma, glioblastoma multiforme, meningioma, craniopharyngioma, schwannoma etc.

Malignancy degree

According to 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. 

Symptoms

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, sleepiness  are frequently encountered symptoms.

Local - symptoms due to local effect on a specific area. Weakness in arms and legs, numbness, visual disturbances, seizures, dizziness, vertigo, hearing impairment and many other symptoms are due to local effect of the tumor.

 

Schematic chart with symptoms of brain 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 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, MR spectroscopy can provide invaluable details. In some cases 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 evolution involve blood hormone levels.

Sagittal Brain MRI

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 sample and subsequent analysis is the cornerstone of brain tumor management.

Treatment

Treatment of brain tumors depends on the type and grade of the tumor. Most primary brain tumors require surgical treatment. Surgery provides material for pathological examination for definite diagnosis and relieves "mass effect" of the tumor. In cases of benign tumors (grade I and II) complete tumor removal provides cure without additional adjuvant therapy. However even benign tumors can be challenging if located in deep or sensitive areas. Unlike in other surgical specialities, neurosurgeons do not routinely practice tumor removal with "safety margins" (i.e. removal of tumor in one piece with some normal tissue around it) since normal tissue removal around tumor may have devastating consequences for the patient. Rather tumor is separated from the normal tissue and removed with minimal damage to surrounding tissue. In cases of malignant primary brain tumors (grade III and IV) the demarcation zone between the normal and abnormal may not be that clear. These tumor show infiltrative growth pattern - i.e. not only they develop as mass inside the brain but also cancer cells dislodge from the main tumor mass to penetrate the normal surrounding brain tissue. In these cases the surgeon may leave some of this transition zone during surgery in order not cause neurological deficit. Yet recurrences develop from remaining tumor cells in the surgical field. To impede the growth of remaining tumor cells radiation therapy (RT) and/or chemotherapy is administered following surgery for malignant brain tumors. Brain tumors do not usually spread to other organs. 

 

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Metastatic tumors are the most frequent type of brain tumors. Nowadays, patients with cancer survive longer than ever before due to medical advances. Unfortunately available treatments are not capable of fully eliminating the tumor from the body. Rather they impede with progression of cancer. Therefore number of patients with metastatic brain tumors is on the rise. Treatment for these tumors should be individual. In the vast majority of cases these patients already had surgery and/or RT with chemotherapy for primary disease. General condition may be poor to undergo a major brain surgery. Surgery is reserved for patients with a few metastasis (oligometastatic disease), good general condition and prognosis. There are several metastatic tumor types very sensitive to radiation and chemotherapy. In these cases adjuvant therapy alone is sufficient. 

In rare cases brain metastasis is the only clinical manifestation of cancer. Search for primary origin may not yield a diagnosis. Therefore surgery can provide pathological specimen for evaluation and diagnosis. 

Metastatic brain tumors were once considered unexceptionally lethal. Yet with modern treatment options, this is not the case anymore. Removing of brain metastasis has been shown to prolong the patient’s survival and increase the quality of life. In the vast majority of cases, chemotherapy and radiation therapy are used to control the tumor growth following surgery for brain metastasis.