Meningiomas are the most common intracranial tumors, making up more than a third of all primary central nervous system (CNS) tumors. The term "meningioma" was first introduced and described in 1922 by Harvey Cushing, a renowned American neurosurgeon. Meningiomas are tumors that grow from the meninges; meninges are the three-layered protective covering of the brain and spinal cord. It is well known that adult females are affected by meningiomas far more frequently than adult males. Meningiomas primarily occur in elderly patients, aged above 65 years. These tumors are exceedingly rare in children. The characteristic and most frequent chromosomal aberration in meningiomas is monosomy 22.
As meningiomas commonly are slow-growing tumors, they often do not cause noticeable symptoms until they are quite large. Some meningiomas may remain asymptomatic for a patient's lifetime or be detected unexpectedly when a patient has a brain scan for unrelated symptoms. When symptomatic, meningiomas present with a wide variety of symptoms, arising from compression of adjacent structures, direct invasion or reactive changes in the brain, or due to obstruction of cerebrospinal fluid (CSF) pathways or vessels.
Signs and symptoms of a meningioma typically begin gradually and may be very subtle at first. Depending on the location of the tumor in the brain, signs and symptoms may include changes in vision, such as double vision or blurriness, headaches, especially those that are worse in the morning, hearing loss or ringing in the ears, memory loss, loss of smell, seizures, weakness in the arms or legs, language difficulty, change in personality or behavior, progressive focal neurologic deficit, confusion, drowsiness, muscle weakness, nausea or vomiting.
Diagnosis is based on various parameters which include eliciting a detailed clinical medical history, followed by personal and family medical history after which a thorough complete physical examination is performed. In addition to which a detailed neurological examination including checks for mental status and memory, cranial nerve function, muscle strength, coordination, reflexes, and response to pain is evaluated.
Imaging scans such as computerized tomography (CT) or magnetic resonance imaging (MRI) are evaluated to help determine the size, location, and type of tumor. In some cases, angiograms of the blood vessels may be necessary. Positron emission tomography (PET) imaging has been used as a diagnostic tool to help delineate healthy tissue from meningiomas. Histological confirmation and verification help to rule out metastasis.
The management protocol for meningiomas is highly individualized and includes a combination of observation, surgical resection, radiotherapy, and rarely chemotherapy.
The “wait-and-see” observation approach is a common strategy used for patients with incidentally diagnosed meningiomas that are small (tumor diameter ≤3 cm) and asymptomatic. These patients are observed and followed with MRI scans until they become symptomatic or until the tumors are considered large enough to treat in order to prevent future symptoms.
Surgical resection is the primary choice for symptomatic, observation failure meningiomas, or large tumors that are anticipated to cause symptoms soon. Gross total resection (GTR) can cure the majority (70–80%) of patients. The goal for surgery is GTR which is dependent on multiple factors.
Technology has improved the surgeon’s ability to precisely locate the tumor, define the tumor’s borders, avoid injury to vital brain areas, and confirm the amount of tumor removal while in the operating room. These include image-guided surgery (IGS), brain mapping functional MRI (fMRI), keyhole and endoscopic surgery, and interoperative MRI or CT.
Radiation therapy uses high-energy X-rays to kill cancer cells and abnormal brain cells and shrink the tumors. The goal of radiation treatment is to maximize the dose to abnormal tumor cells and minimize exposure to normal healthy cells. Indications for radiotherapy include incomplete tumor removal, inoperable tumors, malignant meningioma, and sometimes the patient’s choice. Also, radiation therapy may be an option if the tumor cannot be treated effectively through surgery. Radiation therapy options for meningiomas include stereotactic radiosurgery, fractionated radiotherapy, proton beam therapy, and intensity-modulated radiation therapy (IMRT).
Patients who develop recurrent or progressive meningiomas that no longer respond to surgery or radiotherapy are treated with salvage systemic therapy. Systemic therapies include Hydroxyurea - a chemotherapy drug taken orally that inhibits tumor cell DNA replication. Alpha interferon injections are also a biologic therapy that inhibits tumor blood vessel growth.
Thus meningiomas with complicated histology or in compromising locations have proved to be a challenge in treating and predicting prognostic outcomes. However, ongoing research is currently underway on various molecularly targeted approaches for the treatment of meningiomas.