What are meningiomas?

What Are Meningiomas

Meningiomas are the most common primary intracranial tumors in adults, arising from arachnoid cells of the meninges (the coverings of the brain and spinal cord), accounting for approximately 40% of all primary central nervous system tumors. 1

Origin and Cellular Basis

• Meningiomas develop from arachnoid cells present in the meninges and can therefore occur in any location where meninges or ectopic meninges exist, including unusual anatomical sites such as the nasal cavity, paranasal sinuses, middle ear, orbit, and even the mediastinum. 1
• These are extraaxial neoplasms, meaning they arise outside the brain parenchyma itself but can compress adjacent brain structures. 2

Epidemiology and Demographics

• In adults, meningiomas show a female predominance (3:2 ratio), typically presenting between the third and sixth decades of life, with women affected more than twice as often as men. 1, 3, 4
• In children and young people, there is a male predominance, which contrasts sharply with the adult pattern, with two age peaks: an infantile type (median age 2-3 years) and presentation in the second decade of life. 1
• Meningiomas constitute approximately 15-20% of all intracranial tumors in most series. 3, 4, 2

Tumor Behavior and Grading

• Most meningiomas are benign: 75-80% are classified as CNS WHO grade 1 according to the 5th edition of the WHO Classification of CNS Tumors, representing slow-growing tumors with good prognosis. 1, 3
• 20-25% show higher-risk features: 15-20% are CNS WHO grade 2 (atypical) and 1-5% are grade 3 (malignant), with histopathological or molecular features indicating higher risk of recurrence. 1
• Some meningiomas display aggressive clinical behavior leading to increased patient morbidity and mortality despite being histologically benign. 3

Common Locations

• Up to 90% of pediatric meningiomas are supratentorial or intraventricular in location, with the most common site being the convexity of the cerebral hemispheres. 1
• In adults, typical locations include the cerebral convexity, parasagittal region, sphenoid wing, and skull base. 2
• Less common locations include the posterior fossa, spinal epidural regions, intraventricular spaces, and occasionally completely intraparenchymal without obvious dural attachment. 1

Clinical Presentation

• Headache is the most common presenting symptom, occurring in the majority of patients, typically diffuse and progressive over days to weeks. 5, 6
• Seizures occur in up to 30% of patients, representing focal cortical irritation. 5, 6
• Neurological deficits depend on tumor location and can include motor deficits, visual disturbances (blurred vision, diplopia), personality changes, and cognitive decline. 5, 6
• Signs of increased intracranial pressure include papilledema, nausea, vomiting, and drowsiness, particularly with superior sagittal sinus involvement. 6
• Many meningiomas are now discovered incidentally on neuroimaging performed for other reasons, especially radiation-induced meningiomas in childhood that are found on surveillance scans. 1

Risk Factors and Associated Conditions

• Radiation exposure: Meningiomas can develop after high-dose cranial irradiation for other malignancies (leukemia, astrocytoma, medulloblastoma, retinoblastoma), often occurring in the second decade of life after early childhood radiation. 1, 5
• Neurofibromatosis type 2 (NF-2): 20-40% of pediatric meningiomas develop in patients with NF-2, even when other clinical manifestations are not evident, with higher risk of spinal canal and optic nerve sheath involvement. 1, 5
• Gorlin syndrome (multiple basal cell carcinoma syndrome) is associated with meningiomas, especially in patients who received cranial radiotherapy. 1
• Other genetic syndromes: Rubinstein-Taybi syndrome and rare familial meningioma cases without underlying genetic syndrome have been described. 1

Molecular Characteristics

• The initial cytogenetic event is thought to involve loss of genetic material on the long arm of chromosome 22 (22q12), near the NF-2 gene. 1
• Pediatric meningiomas frequently show 1p and 14q deletions, which are associated with higher risk of tumor recurrence. 1
• Radiation-induced meningiomas infrequently show NF-2 gene abnormalities but often exhibit complex structural and numerical chromosomal abnormalities consistent with radiation-induced DNA damage. 1
• Multiple recurring molecular aberrations have been identified including alterations in NF2, AKT1, SMO, SMARCE1, PIK3CA, CDKN2A/B, and others, though none have reached "ready for clinical use" classification for targeted therapy selection. 1

Diagnostic Features

• MRI with contrast is the gold standard, revealing homogeneous dural-based enhancement with a characteristic "dural tail" sign. 7
• CT scan provides complementary information, particularly for detecting calcifications present in up to 50% of cases. 7
• Typical imaging shows a homogeneous, hemispheric, markedly enhancing extraaxial mass, though atypical features like ring enhancement, large meningeal cysts, and metaplastic changes can be misleading. 2

Treatment Principles

• Surgical resection remains the treatment of choice, with complete resection including dural attachment being optimal when feasible. 1, 7, 3
• Postoperative radiotherapy may be considered based on extent of resection and histological grade. 1
• Stereotactic radiosurgery or fractionated radiotherapy is used for recurrent, surgically inaccessible, or partially excised tumors, particularly atypical or malignant variants. 7, 3
• For progressive or recurrent meningioma after surgery and radiotherapy, additional treatment options are limited due to lack of proven efficacy, with no established systemic therapy standards. 1

Prognosis

• Most benign meningiomas have good long-term prognosis after treatment with appropriate surgical resection. 3
• Recurrence rates are higher with subtotal resection, necessitating adjuvant radiation therapy and long-term surveillance. 7
• Multiple meningiomas (occurring in 1-10% of patients, though recent data suggest higher incidence) should be regarded as a chronic disease where cure is seldom possible and disease control is the management goal. 8