Meningioma

Meningiomas are almost always benign, slow-growing brain tumors that arise from arachnoid cap cells of the arachnoid villi. As meningiomas may remain asymptomatic for long periods of time, they are often an incidental finding. Tumor compression can lead to a wide variety of neurological symptoms (i.e., headaches, seizures, paresthesias) that are generally specific to the structure(s) being compromised. Contrast imaging typically shows an enhanced round tumor with well-defined margins that often resembles a snowball. Management depends on the location and grade of the tumor, as well as patient-specific factors such as age, comorbidities, and accompanying symptoms. Treatment generally consists of surgical intervention, radiotherapy, or a combination of both. In some cases (e.g., asymptomatic elderly patients, or those with slow-growing meningiomas), a "watch and wait" approach with regular tumor monitoring may be safer than invasive therapy.

Meningiomas are a diverse group of brain tumors that arise from the arachnoid layer (specifically the arachnoid cap cells) and can therefore occur in any part of the CNS with a meningeal covering.

• Most common benign primary brain tumor in adults ^[1][2]
• Sex: ♀ > ♂ (2:1) ^[3]
• Age: most common in patients > 65 years of age ^[4]

Epidemiological data refers to the US, unless otherwise specified.

• Mostly idiopathic ^[5]
• Exposure to ionizing radiation: radiotherapy for head and neck tumors, dental x-rays ^[6]
• Multiple meningiomas may develop in patients with neurofibromatosis type II. ^[7]

• General clinical features ^[6]
  • Mostly asymptomatic
  • General symptoms of CNS tumors (e.g., seizures and focal neurologic signs)

MRI (imaging modality of choice)

• Plain MRI findings ^[16]
  • Round, sharply demarcated space-occupying lesion with radiological features of an extra-axial tumor
  • Dural tail sign
  • T1: isointense or hypointense
  • T2: isointense or hyperintense
• Contrast MRI findings ^[16]
  • Significant homogenous enhancement of the meningioma
  • Sunburst or spoke-wheel appearance ^[17]
  • Spinal meningioma: ginkgo-leaf sign ^[18]
    • The enhanced but distorted spinal cord takes the shape of the leaf, while the stretched non-enhancing dentate ligament forms the "stem" of the leaf.
    • Seen on an axial view of the spinal cord after contrast enhancement
  • En plaque meningioma: a rare benign subtype that is characterized by diffuse carpet-like growth along the dural layer

CT scan ^[19]

• CT scans performed to investigate unexplained headaches or seizures are usually the first to pick up incidental meningiomas.
• Findings
  • Hyperdense or isodense well-demarcated extra-axial mass
  • Possible calcifications

Brain tumor biopsy ^[6]

• May be performed if the tumor is inoperable or imaging is inconclusive
• Most meningiomas are removed surgically without a prior biopsy. ^[20]

Gross findings

• Encapsulated, round, grayish-white tumor
• Firm to hard consistency
• Cross-sectional surface: gray, granular

Microscopic findings

• Mesenchymal origin (arachnoid cap cells)
• Whorls of meningothelial cells (onion peel arrangement) ^[21]
• Psammoma bodies ^[22]
• Increased vascularity ^[23]

WHO classification of meningiomas

• There are 15 histological subtypes of meningiomas.
• Most meningiomas are benign (WHO grade I) tumors.

• Surgical resection: first-line treatment ^[22]
  • Preoperative embolization in the case of highly vascular tumors ^[23]
  • Skull base meningiomas have a high recurrence risk . ^[24]
• Radiotherapy ^[22]
  • In the case of inoperable tumors
  • Postoperatively, if the tumor was incompletely resected
  • As an adjuvant therapy in the case of grade II and III meningiomas
  • Small tumors (usually < 3 cm): stereotactic radiosurgery (e.g., gamma knife) ^[25]
• Active surveillance: consider in a slow-growing asymptomatic tumor in an elderly patient ^[6]

• WHO grade I meningiomas: good prognosis, with a 5-year recurrence rate of 7–23% after resection ^[22][26]
• WHO grade II and III meningiomas: poor prognosis, with a 5-year recurrence rate of ∼ 50% and ∼ 75% respectively after resection ^[22][26]

• MIB-1 index: an indirect measure of the rate of tumor growth ^[28][29]
  • MIB-1 is a monoclonal antibody used to assay the antigen Ki-67 (a nuclear protein seen in proliferating cells).
  • MIB-1 index > 4% is associated with a higher meningioma recurrence rate.