Difference Between Meningioma and Glioma
Meningiomas and gliomas are two types of commonly-occurring primary brain tumour. While they can present with similar symptoms, such as headaches, impaired vision and psychological symptoms, they are fundamentally different.
What is a Meningioma?
Meningiomas are tumours that originate in the meninges. The meninges are the protective layers surrounding the brain and the spinal cord. They are fairly common, accounting for 13 - 30% of primary brain tumour cases [1, 2]. They are common in middle- to late-aged adults, and occur more commonly in women [3].
The presentation of meningiomas depends on their location. As meningiomas don't grow in the brain directly, they cause symptoms by compressing the brain. The most common symptoms include headaches, reported in approximately 67% of cases. More symptoms include seizures (reported in 40% of cases) and visual impairment (reported in 38% of cases) [4]. Additionally, patients can experience feeling of pressure inside their head, other neurological deficits or psychiatric symptoms including mood swings, memory disturbance and psychosis [5].
How are Meningiomas Diagnosed?
Meningiomas are primarily diagnosed using imaging - magnetic resonance is the most common method used [6]. The meningioma's characteristic features are visible (including shape, contour, and location) on MRI, allowing for a definitive diagnosis in some cases. Sometimes, a biopsy and subsequent histological evaluation is used for diagnosis [6]. Following imaging, the tumours can be classified, with 90% being classified as benign, 2% as malignant, and 6% as atypical [7, 8].
How are Meningiomas Treated?
As most meningiomas are benign (they do not spread), observation is the preferred management option. However, the largest disadvantage of the observation approach is that histological evaluation is impossible without a biopsy.
Alternatively, the primary course of treatment is surgical removal (resection), which is often curative [3]. The extent of the surgery, and the approach is determined based on the imaging study obtained at the diagnosis. However, if the surrounding anatomy complicates surgery and the tumour cannot be resected, radiotherapy to the tumour site is indicated to shrink the tumour and/or kill the cancer cells that could be left behind [9].
For meningiomas, a variety of radiosurgery tools have been developed, including the Leksell Gamma knife, or Cyberknife [8]. These tools allow for a very precise delivery of radiation to the specified area of the brain. If the tumour is impossible to operate on, has metastasised, or doesn't respond to other treatments, systemic chemotherapy may be considered [7].
Meningioma Prognosis
Consequently, the prognosis for meningioma is generally good, especially with the benign tumours that were removed surgically [4]. However, incompletely resected tumours, or those classified as malignant or atypical, may be more complicated and therefore have worse prognosis [8].
The prognosis also depends on the patient's age, as well as the characteristics of the tumour. Additionally, the presence of neurological and psychiatric symptoms usually worsens prognosis [5].
What is a Glioma?
Gliomas are a type of brain tumour that originates from the glial cells. The glial cells themselves are support cells of the nervous system and provide protection and support to the neurons in the brain.
There are multiple types of glial cells, including astrocytes, oligodendrocytes, microglia and ependymal cells. All of these cells can undergo malignant transformation, becoming a subtype of glioma (consequently named include astrocytic gliomas, oligodendrocytic gliomas, ependymomas after the cell of origin).
Additonally, gliomas can be of the mixed cell population type [6]. As the glial cells are the most abundant type of cell in the brain, gliomas are a very common type of brain tumour, accounting for 81% of intracranial tumours [10].
Symptoms of a Glioma
As with all brain tumours, the symptoms and presentation vary based on the location of the tumour.
The most common symptom is a headache, which occurs in 30 to 50% of people. Other symptoms include blurred vision, hearing loss, speech impairment or seizures. Additionally, 20 to 40% of patients experience a change in personality with a glioma.
Gliomas can also present with a variety of nonspecific symptoms, including nausea and vomiting, fatigue, muscle weakness, and loss of appetite [11]. Additionally, advanced and metastatic gliomas can present with motor disorders, such as inability to move on one side (hemiparesis) [6].
How are Gliomas Diagnosed?
Gliomas are diagnosed primarily by imaging, with MRI being the gold standard of diagnosis. As gliomas are aggressive and infiltrate surrounding tissues, histological and molecular characterisation is important to develop a treatment plan [10].
Therefore, imaging is followed by histological examination following a biopsy or surgical resection. This involves taking a sample of the tumour, cutting it into very thin slices and examined under the microscope after staining with specialised dyes that allow visualisation of certain molecules or structures [12, 6].
How are Gliomas Treated?
Consequently, the treatment of glioma largely depends on the outcome of the histological and molecular evaluation.
Surgery is an option, which can be curative for low-grading gliomas. If a tumour cannot be removed, radiotherapy to the tumour site is indicated.
However, gliomas are often very aggressive and infiltrate surrounding tissue. Therefore, more intense therapeutic approach is often required, including postoperative radiotherapy to the site of the tumour, as well as chemotherapy.
The standard of care includes nitrosourea-based chemotherapies, such as carmustine, a combination of procarbazine, lomustine and vincristine, or a combination of thioguanine, procarbazine, lomustine and hydroxycarbamide (hydroxyurea) [6].
Prognosis of Gliomas
Unfortunately, due to their aggressiveness, the prognosis for gliomas is generally poor. Following surgery, gliomas often tend to relapse (come back), and the five-year survival rate is only 6.1% [9]. Prognosis depends on age, the grade and location of the tumour, and pre- and post-operative performance of the patient [13].
Glioma vs Meningioma: A Comparison
From a pathophysiology standpoint, the tumours originate from different cells. Meningiomas originate from the meninges - the protective layers of the brain and spinal cord. Gliomas originate from the glial cells, which are cells located around the neurons and have supportive and protective functions [14].
Genetically, the tumours harbour different mutations and this can be used to to distinguigh between the two tumours. For example, in a case of a glioblastoma occuring with a meningioma at the same location, mutations in the isocitrate dehydrogenase genes and TERT promoters were used to distinghush between the two tumours in a case study [15].
On imaging, the tumours present differently. Meningiomas appear well-defined with clear margins, and appear homogeneous with contrast. On the other hand, gliomas look more diverse, showing irregular margins, appear more heterogeneous, and contain regions of edema (swelling) [16].
Conclusion
While both meningiomas and gliomas are common brain tumours which can present with similar symptoms, they are different in the cells of origin, genetic characteristics, and imaging findings and prognosis.
