by Kristopher D. Langdon MD PhD FRCPC
June 7, 2023
A meningioma is a tumour that starts in the meninges, a thin layer of tissue that covers the outside of the brain and spinal cord. The tumour is made up of specialized meningothelial cells that are normally attached to a part of the meninges called the dura. A meningioma can develop in any location where the dura is normally found.
Most meningiomas are slow-growing and behave like non-cancerous tumours. However, as a result of the pressure they put on the brain and spinal cord, they can be life-threatening. Faster-growing meningiomas are less common and may require different treatments.
As it grows the tumour usually pushes the inside layers of the meninges towards the brain and spinal cord. Although most meningiomas do not grow directly into the brain or spinal cord, the pressure it puts on the brain or spinal cord can cause serious neurological symptoms. The symptoms experienced will depend on the area of the brain or spinal cord affected by the tumour.
Most patients diagnosed with meningioma are over 60 years of age and they are twice as common in females compared to males. For this reason, some doctors believe that female hormones such as progesterone may play a role in the development of meningioma.
Prior radiation to the head, especially when received at a young age, increases the chances of developing a meningioma at a later age. Patients with the genetic syndrome neurofibromatosis type 2 (NF2) are also at an increased risk for developing multiple meningiomas. For most patients with meningioma, the cause remains unknown.
A biopsy is a surgical procedure that removes a small piece of tissue for examination by a pathologist. The purpose of a biopsy is to establish a diagnosis. A test called immunohistochemistry may be performed to confirm the diagnosis. Your doctors will use this information to plan treatment such as surgery or radiation therapy.
After the tumour has been removed completely, it will be sent to a pathologist who will prepare another pathology report. This report will confirm or revise the original diagnosis. If additional immunohistochemical or molecular tests are performed, the results will be described in this report.
Pathologists use the term grade to describe how different the tumour cells in a meningioma look and behave compared to normal meningothelial cells. In order to determine the tumour grade, pathologists use guidelines created by the World Health Organization (WHO). According to the WHO guidelines, a meningioma can be given a grade of I, II, or III. The grade is important because it predicts how aggressive the tumour is likely to be. Specifically, higher-grade meningiomas are more likely to grow back after treatment and may be more difficult to treat.
There are different types of meningioma based on how the tumour cells look when examined under the microscope. The tumour type is important because it is used to determine tumour grade. Other features such as the size and shape of the tumour cells, the number of dividing tumour cells, and the presence of tumour cells spreading into the brain are also used to determine the grade. These features are described in more detail below.
Grade I meningiomas behave like non-cancerous tumours. These tumours are usually discovered because they press against the brain or spinal cord and cause neurological symptoms for the patient. Some tumours are discovered incidentally when imaging is performed for another reason.
Unless your pathologist sees other concerning features (see below), the following types of meningioma are usually considered grade I:
The behaviour of a grade II meningioma depends on how the tumour looks when examined under the microscope. The behaviour can range from benign to aggressive. Chordoid and clear cell type meningiomas are both considered grade II.
A meningioma can also be classified as grade II if it shows any of the following features:
Grade III meningiomas are aggressive tumours that behave like malignant tumours (cancer). Papillary and rhabdoid-type tumours are considered grade III meningiomas. A meningioma can also be considered grade III if tumour cells dividing to create new tumour cells are easily found. This process is called mitosis and the dividing tumour cell is called a mitotic figure.
Your pathologist may perform a test called immunohistochemistry on a sample from your tumour. This test allows your pathologist to see the proteins being made by the tumour cells. If the tumour cells are making a protein, the result will be described as positive or reactive. If the cells are not making the protein, the result will be described as negative or non-reactive.
Meningiomas typically show the following results:
Depending on the type of meningioma, your pathologist may order additional immunohistochemical tests and these will be described in your report.