Revision 203 for 'Meningioma'

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Meningioma

Meningiomas are extra-axial tumors and represent the most common tumor of the meninges. They are a non-glial neoplasm that originates from the meningocytes or arachnoid cap cells of the meninges. They are typically benign with a low recurrence rate but rarely can be malignant.

Typical meningiomas appear as dural based masses isointense to grey matter on both T1 and T2 weighted imaging, and demonstrate vivid contrast enhancement on both MRI and CT. There are, however, many variants some of which can vary dramatically in their imaging appearance.

A broad division of meningiomas is into primary intradural (which may or may not have secondary extradural extension) and primary extradural 18.  They can also be classified according to location (e.g. spinal, intraosseous, intraventricular etc.), by histological variants (e.g. clear cell, rhabdoid etc.) and by etiology (e.g. radiation induced etc.). 

This article is a general discussion of meningioma focusing on primary intradural meningiomas and the imaging findings of intracranial disease.

For spinal disease refer to spinal meningioma.

Epidemiology

Meningiomas are more common in women, with a ratio of 2:1 intracranially and 4:1 in the spine. Atypical and malignant meningiomas are slightly more common in males. They are uncommon in patients before the age of 40 and should raise suspicion of neurofibromatosis type 2 (NF2) when found in young patients.

Clinical presentation

Many small meningiomas are found incidentally and are entirely asymptomatic. Often they cause concern as they are mistakenly deemed to be the cause of vague symptoms, most frequently headaches. Larger tumors or those with adjacent edema or abutting particularly sensitive structures can present with a variety of symptoms. Most common presentations include 8:

  • headache: 36%
  • paresis: 22%
  • change in mental status: 21%
  • focal neurological deficits

Meningiomas may also become clinically apparent due to complications dependent on location including:

  • convexity/parasagittal: seizures and hemiparesis
  • basisphenoid: visual field defect
  • cavernous sinus: cranial nerve deficit(s)
  • frontal: anosmia (although often become very large before becoming symptomatic)
  • dural venous sinus invasion/dural venous sinus thrombosis (usually this occurs gradually and even occlusion is asymptomatic, with collateral veins having time to enlarge)
  • intraosseous extension: may be hyperostotic or osteolytic and may result in local mass effect (e.g. proptosis)

Pathology

Meningiomas are thought to arise from meningocytes or arachnoid cap cells, which themselves arise from pluripotential mesenchymal progenitor cells, which accounts for sometimes unusual location of primary extradural tumors 18-19

Although the majority of tumors are sporadic, they are also seen in the setting of previous cranial irradiation and of course in patients with neurofibromatosis type II (NF2) (Merlin gene on Chromosome 22). Additionally meningiomas demonstrate estrogen and progesterone sensitivity and may grow during pregnancy.

Grading

Grading of meningiomas follows the WHO classification for CNS tumors 7, 11:

  • grade I: 'benign" (70%)
    • transitional (mixed) (40%)
    • meningothelial (17%)
    • fibrobrous (7%)
    • microcystic
    • psammomatous
    • angiomatous *
    • secretory subtypes
    • metaplastic
    • lymphoplasmacyte-rich
  • grade II: "atypical" (30%)
    • clear cell
    • chordoid
    • atypical by histological criteria (29%) 11
      • 4 to 19 mitoses per ten high-power fields
      • infiltration into brain parenchyma **
      • 3 or more of the following 5 histologic features: necrosis, sheet-like growth, small cell change, increased cellularity, prominent nucleoli
  • grade III: "anaplastic" or "malignant" (~1%)
    • rhabdoid
    • papillary
    • anaplastic by histological criteria 11
      • obvious malignant features similar to those seen in melanoma, carcinoma, or high grade sarcoma
      • 20 or more mitosis per ten high-power fields

* Hemangiopericytomas were, until 1993, considered angiomatous meningiomas, but are not classified as a separate entity; "Other neoplasms related to the meninges" according to WHO 2007 classification of CNS tumors

** It is important to note, when reading older literature, that in the WHO 2007 classification, infiltration into brain parenchyma of another wise "benign" grade I tumor was sufficient to designate it a grade II tumor. As such, incidence of grade II tumors increased to ~30% 11.

Macroscopic

In general, there are two main macroscopic forms easily recognized on image studies:

  • globose: rounded, well defined dural masses, likened to the appearance of a fried egg seen in profile (the most common presentation)
  • en plaque: extensive regions of dural thickening
Variants
Radiographic features

Meningiomas are located anywhere that meninges are found, and in some places where only rest cells are presumed to be located. Locations include:

Edema may be present associated to some meningiomas and the underlying mechanisms for this is related to:

  • venous stasis/occlusion/thrombosis
  • compressive ischemia
  • aggressive growth/invasion
  • parasitisation or pial vessels
  • vascular endothelial growth factor (VEGF) producing lesion
Plain radiography

Plain films no longer have a role in the diagnosis or management of meningiomas. Historically a number of features were observed, including:

  • enlarged meningeal artery grooves
  • hyperostosis or lytic regions
  • calcification
CT

CT is often the first modality employed to investigate neurological signs or symptoms, and often is the modality which detects an incidental lesion:

  • Non-contrast CT
    • 60% slightly hyperdense to normal brain, the rest are more isodense
    • 20-30% have some calcification 8
  • Post-contrast CT
    • 72% brightly and homogeneously contrast enhance 8
    • malignant or cystic variants demonstrate more heterogeneity / less intense enhancement {ref needed}
  • hyperostosis
    • typical for meningiomas that abut the base of the skull
    • need to distinguish reactive hyperostosis from:
  • enlargement of the paranasal sinuses (pneumosinus dilatans) has also been suggested to be associated with anterior cranial fossa meningiomas 20
  • lytic / destructive regions are seen particularly in higher grade tumors, but should make one suspect alternative pathology (e.g. hemangiopericytoma or metastasis) {ref needed}
MRI

As is the case with most other intracranial pathology, MRI is the investigation of choice for the diagnosis and characterization of meningiomas. When appearance and location is typical, the diagnosis can be made with a very high degree of certainty. In many instances however the appearances are atypical.

Meningiomas typically appear as extra-axial masses with a broad dural base. They are usually homogeneous and well circumscribed, although many variants are encountered.

Signal characteristics of typical meningiomas include:

  • T1
    • isointense to grey matter: ~60-90% 3,8, 13
    • somewhat hypointense: 10-40% compared to grey matter
  • T1 C+ (Gd): usually intense and homogeneous enhancement
  • T2
    • isointense to grey matter: ~50% 3,8,13
    • hyperintense: 35-40%
      • usually correlates with soft texture and hypervascular tumors 13
      • very hyperintense lesions may represent the microcystic variant 12
    • hypointense to grey matter: 10-15% compared to grey matter and usually correlates with harder texture and more fibrous and calcified contents
  • DWI: atypical and malignant subtypes may show greater than expected restricted diffusion although recent work suggests that this is not useful in prospectively predicting histological grade 15-16
  • MR spectroscopy: Usually it does not play a significant role in diagnosis but can help distinguish meningiomas from mimics. Features include:
    • increase in alanine (1.3-1.5 ppm)
    • increased glutamine/glutamate
    • increased choline (Cho): cellular tumor
    • absent or significantly reduced N-acetylaspartate (NAA): non-neuronal origin
    • absent or significantly reduced creatine (Cr)
  • MR perfusion: it has good correlation between volume transfer constant (k-trans) and histological grade

Helpful signs include

  • CSF vascular cleft sign, which is not specific for meningioma, but helps establish the mass to be extra-axial; loss of this can be seen in grade II and grade III which may suggest brain parenchyma invasion
  • dural tail seen in 60-72% 2 (note that a dural tail is also seen in other processes)
  • sunburst or spokewheel appearance of the vessels

Meningiomas typically narrow arteries which they encase. This is a useful sign to distinguish a meningioma from a pituitary macroadenoma which will not.

Edema can be seen and correlates with size, rapid growth, location (convexity and parasagittal > elsewhere), and invasion in the case of malignant meningiomas.

Angiography (DSA)
  • mother-in-law sign: "comes early, stays late, very dense", tumor blush
  • dual blood supply from both
    • pial (ICA) supplies periphery
    • meningeal vessels (ECA) supplies core
  • spoke wheel appearance
  • dense venous filling
  • preoperative embolization: especially skull base, particles are favored; 7-9 days prior to surgery

    Treatment and prognosis

    Treatment is usually with surgical excision. If only incomplete resection is possible (especially at the base of skull) then external-beam radiation therapy can be used 8.

    The Simpson grade correlated the degree of surgical resection completeness with with symptomatic recurrence.

    Recurrence rate varies with grade and length of follow-up 8, 21

    • grade I = 7-25%
    • grade II = 29-52%
    • grade III = 50-94%

    Metastatic disease is rare, but has been reported 8.

    History and etymology

    The term "meningioma" was first introduced by Harvey Cushing, neurosurgeon, in 1922 9.

    Differential diagnosis

    The differential diagnosis largely depends on location, and generally includes other dural masses:

    In the setting of hyperostosis consider:

    In the setting of lucent intraosseous meningioma the differential is essentially that of a solitary lucent lesion of the skull.

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