Meningioma

What is a meningioma?

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 treatment.

Meninges

The entire brain and spinal cord are covered by a specialized type of tissue called meninges. The meninges are made up of multiple layers and each layer serves a different purpose. The thickest layer is found closest to the skull and vertebral bones and it is called the dura mater (dura, for short). The dura helps to protect the brain and spinal cord by serving as a barrier and sealing in the fluid (cerebral spinal fluid) that surrounds both organs. The dura is covered by specialized meningothelial cells.

Symptoms of meningioma

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.

What causes meningioma?

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.

Your biopsy report for meningioma

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.

Your pathology report after the tumour has been removed

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.

World Health Organization (WHO) Grading

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

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:

• Meningothelial
• Fibrous (fibroblastic)
• Transitional (mixed)
• Psammomatous
• Angiomatous
• Microcystic
• Secretory
• Lymphoplasmacyte-rich
• Metaplastic

Grade II

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:

• Brain invasion: The meningioma tumour cells have broken through the meninges (brain covering) and entered the brain tissue. This is a sign that the tumour may be more aggressive.
• Increased mitotic activity: A tumour cell that is in the process of dividing to create new tumour cells is called a mitotic figure. Tumour cells undergo a process called mitosis to create new tumour cells.
• Increased cellularity: This means that there are more tumour cells than would be typically expected for a meningioma.
• Small cells with a high nuclear-to-cytoplasmic ratio: The nucleus is the part of the cell that contains genetic material or DNA. The cytoplasm is the body of the cell that surrounds the nucleus. Small cells have less cytoplasm which makes the nucleus look bigger than normal.
• Prominent nucleoli: The nucleolus is a large piece of genetic material found inside the nucleus of some cells. A cell that is preparing to divide may have a large, easy to see nucleolus. These are often seen in more aggressive tumours. If more than one is seen they are called nucleoli.
• Sheeting: An abnormal pattern of growth where the tumour cells are arranged in a back-to-back and side-to-side fashion.
• Necrosis: Necrosis is a form of cell death. Necrosis is more common in fast-growing tumours. Necrosis can also be seen after treatment such as radiation or chemotherapy.

Grade III

Grade III meningiomas are aggressive tumours that behave like a malignant tumour (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.

Immunohistochemistry

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:

• Embryonic membrane antigen (EMA) – Positive.
• Vimentin – Positive.
• Somatostatin receptor 2A – Positive.
• E-cadherin – Positive.
• Progesterone receptor (PR) – Positive.

Depending on the type of meningioma, your pathologist may order additional immunohistochemical tests and these will be described in your report.

by Kristopher D. Langdon MD PhD FRCPC (updated July 20, 2021)