What is central nervous system tumor
The Central Nervous System (CNS) comprises the brain and the spinal cord, and its tumors occur due to the growth of abnormal cells in the tissues of these locations. Approximately 88% of primary Central Nervous System tumors occur in the brain.
Primary CNS cancer accounts for 1.4% to 1.8% of all malignant tumors worldwide and is responsible for a disproportionate rate of morbidity and mortality.
Primary brain tumors, those that originate in the brain, rarely spread to other parts of the body, but even those considered benign and of slow growth can press on and destroy normal brain tissue, causing irreversible neurological damage or even death.
Subtypes of Central Nervous System Tumors
It’s important to understand the difference between tumors that originate in the brain (primary brain tumors) and tumors that start elsewhere and spread to the brain (secondary or metastatic). In adults, metastatic brain tumors are more common than primary brain tumors.
Primary CNS tumors encompass a wide range of pathological entities, each with a distinct natural history. To simplify, CNS tumors can be classified as gliomas or non-gliomas. Currently, morphological and genetic characteristics are found in each type of tumor and help in the proper diagnosis and classification of these tumor types.
The prognosis for patients with benign brain tumors is generally very favorable. However, patients with malignant primary or metastatic brain tumors often die from the disease.
The main types of primary CNS tumors are:
- Meningiomas – these are usually benign and originate in the meninges, the layers covering the brain and spinal cord. The incidence rate is approximately 2 cases per 100,000 individuals. They are more common in women in their sixth and seventh decades of life and are the most common primary brain tumors in adults. Many meningiomas are found incidentally on imaging studies and do not require treatment at the time of initial diagnosis. For patients with asymptomatic meningioma, observation may be a management option. If a mass effect is observed in patients with or without symptoms, the treatment of choice is usually complete surgical resection. Radiation therapy may also be used as a stand-alone or adjuvant treatment in this type of tumor;
- Pituitary Adenomas – pituitary tumors are typically functional or non-functional adenomas. Endocrine abnormalities may be found at presentation if the tumors are producing peptides such as prolactin, growth hormone, or adrenocorticotropic hormone;
- Gliomas – these are primary brain tumors originating from neuroglial stem cells or progenitor cells. Based on their histological appearance, immunohistochemical study, and molecular profile, they are classified as pilocytic astrocytomas, IDH-mutant astrocytomas grade 2, 3, or 4, 1p19q co-deleted IDH-mutant oligodendrogliomas grade 2 or grade 3, wild-type IDH glioblastoma grade 4, and ependymomas;
- Medulloblastomas – these are fast-growing tumors, considered grade IV by the WHO. They can be treated with surgery, radiation therapy, and chemotherapy. They are more common in children – with the peak incidence between 2 and 7 years of age – but young adults can also present with them.
Symptoms and Signs of Central Nervous System Tumors
The symptoms of brain tumors can occur gradually, worsening over time, or they can appear suddenly. The presenting symptoms of a brain tumor are related to mass effect, parenchymal infiltration, and tissue destruction. Headache, the most common symptom, is related to the mass effect and occurs in approximately 35% of patients.
Intracranial hypertension can be caused by tumor growth, edema in the brain, or blockage of cerebrospinal fluid (CSF) flow, leading to symptoms such as headache, nausea, vomiting, blurred vision, balance problems, changes in personality or behavior, seizures, and drowsiness.
There are three main groups of symptoms to watch for:
- Headache with alarms: Not every common headache raises suspicion of CNS tumors, only when it presents some alarm sign. These alarms are usually the onset of a new headache (for those who have never experienced this type of headache), a change in the headache pattern (for those who already had headaches before), worsening intensity (when it becomes stronger over time), increased frequency (when the headache occurs more often), or when the pain is fixed (it always appears in the same place);
- Epilepsy or other seizures: Especially when the patient has a seizure for the first time;
- Loss of neurological functions: These are called focal deficits – when there is loss of strength or sensation in the limbs, loss of vision or hearing, changes in speech or intellectual ability (comprehension, reasoning, writing, calculation, recognition of people), changes in behavior (apathy, agitation, or aggressiveness) compared to the person’s normal pattern.
The appearance of one or more of these alterations should always be reported to the doctor and investigated appropriately.
Diagnosis of central nervous system tumor
The patient’s medical history, physical examination, and neurological examination with abnormalities are the starting point for suspecting CNS tumors. Upon clinical suspicion, complementary tests are performed to search for CNS neoplasms. The first tests are imaging exams:
- Magnetic resonance imaging (MRI) – a diagnostic method that uses electromagnetic waves to form images. MRI produces images that allow determination of the size and location of a tumor, as well as the presence of metastases; and
- Computed tomography (CT) – an imaging diagnostic technique that uses X-rays to visualize small slices of body regions. It can be used in some cases where MRI is not a good option, such as for overweight patients or those with claustrophobia. CT also provides better detailing of the bony structures near the tumor.
Lumbar puncture is used to diagnose cancer cells in the cerebrospinal fluid (CSF), which bathes the spinal cord and brain. The procedure involves aspiration of CSF through a needle, for subsequent examination. This test can help evaluate the cerebrospinal dissemination of some types of CNS tumors, such as medulloblastoma.
Blood and urine tests can also be performed. Although laboratory tests are rarely part of the diagnosis of brain and spinal cord tumors, they may be performed to check the functioning of other organs, such as the liver and kidneys, especially if surgery and chemotherapy are planned.
Treatment for CNS tumors
Treatment for CNS tumors is complex and involves a multidisciplinary team of different healthcare professionals.
It typically starts with a neurosurgeon for tumor removal or tissue biopsy. The next steps and progression depend on the specific type of tumor, as indicated in the pathology report, involving a medical oncologist for chemotherapy planning and a radiation oncologist for radiation therapy planning.
Surgery for brain and spinal cord tumors can be done to obtain a biopsy sample, remove the tumor (or as much of it as possible), or help prevent or treat symptoms or potential complications of the tumor.
Learn about the treatment options for CNS tumors below.
Surgery for tumor removal
Most often, it is the first step in treating a brain or spinal cord tumor, and is indicated as long as it is safe and does not affect normal brain function.
The goals of surgery are:
- Diagnosis, providing tissue for histological and molecular analysis for proper tumor classification;
- Reduce mass effect, preserving the patient’s neurological function;
- Promote cytoreduction, that is, reduce the size of the tumor; and
- Treat hydrocephalus, if present.
Advancements in neuroanesthesia, microneurosurgical techniques, and instrumentation have decreased the risk of surgery. When therapeutic intervention is considered appropriate, surgery remains the initial therapy for almost all patients with brain tumors and can be curative for most benign tumors, including meningiomas.
Due to the infiltrative nature of most primary brain tumors, relief of mass effect and volume reduction result in symptomatic improvement and allow for the safe administration of adjuvant treatment with radiotherapy, with or without chemotherapy.
Radiotherapy
Radiotherapy is an essential component in the treatment of many patients with brain tumors. It can be curative for some patients and can prolong survival in the vast majority of cases where it is applied.
It can be used in different situations:
- After surgery, to kill any remaining tumor cells;
- As the primary treatment if surgery is not a good option; and
- In combination with chemotherapy; and
- In some cases where the disease recurs.
Chemotherapy
They are cancer-fighting drugs that can be administered intravenously or orally, entering the bloodstream and reaching almost all areas of the body. They help in the complementary treatment of CNS tumors associated with surgery, radiotherapy, or, in some cases, when used alone.
Targeted drugs
As researchers have learned more about how tumor-causing cells function or how they help tumor cells grow, new drugs have been developed that specifically target these changes. These are targeted drugs that, by preferentially attacking the molecular characteristics present in tumor cells, are generally less aggressive to normal cells and more effective against the tumor.
These drugs do not yet play a major role in the treatment of brain or spinal cord tumors, but some of them may be useful for certain types of tumors.
Currently, it is known that multimodal therapy with surgery, radiotherapy, and chemotherapy clearly reduces morbidity, prolongs survival, and can be curative in some patients. Given the limitations of current therapies, efforts to improve outcomes based on the identification of molecular targets present in the tumor are growing.
