Meningioma

Meningiomas are extra-axial tumours and represent the most common tumour of the meninges. They are a non-glial neoplasm that originates from the meningocytes or arachnoid cap cells of the meninges, and are located anywhere that meninges are found, and in some places where only rest cells are presumed to be located. Although they usually easily diagnosed, and are typically benign with a low rate of recurrence following surgery, there are a large number of histological variants with variable imaging features and in some instances more aggressive biological behaviour.

A broad division of meningiomas is into primary intradural (which may or may not have secondary extradural extension) and primary extradural (rare) 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 aetiology (e.g. radiation induced etc.).

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. Some of the aforementioned variants can, however, vary dramatically in their imaging appearance.

This article is a general discussion of meningioma focusing on typical primary intradural meningiomas and the imaging findings of intracranial disease. For spinal and primary extradural tumours refer to spinal meningioma and primary extradural meningioma articles respectively. Many of the  histological variants are also discussed separately.

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 tumours or those with adjacent oedema 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%

Meningiomas may also become clinically apparent due to mass effect their location:

Occasionally transosseous or intraosseous involvement with prominent hyperostosis may result in local mass effect (e.g. proptosis).

It should be noted that although dural venous sinus invasion and occlusion is not infrequent, as this usually this occurs very gradually most are asymptomatic, as collateral veins have had time to enlarge.

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 tumours 18-19.

Although the majority of tumours 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 oestrogen and progesterone sensitivity and may grow during pregnancy.

Grading

Grading of meningiomas follows the WHO classification for CNS tumours  and includes both usual histological features ( e.g. mitotic index) as well as a number of histological subtypes, some of which have been associated with more aggressive behaviour 7, 11, 23:

* Haemangiopericytomas were, until 1993, considered angiomatous meningiomas, but in the 2007 WHO classification of CNS tumours they were classified as a separate entity under "Other neoplasms related to the meninges". This again changed in 2016 when the classification was updated. Haemangiopericytomas and solitary fibrous tumours of the dura are considered different manifestations of the same disease, listed under "mesenchymal, non-meningothelial tumours" as a single entry. 

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

Macroscopic

In general, there are two main macroscopic forms easily recognised 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

The cut surface reflects the various histologies encountered, ranging from very soft to extremely firm in fibrous or calcified tumours. They are usually light tan in colouring, although again this will depend on histological subtypes.

Radiographic features

In addition to histological variants, many of which have 'atypical' imaging appearances, a number of 'special examples' of meningiomas are best discussed separately. These include:

The remainder of this section focuses on more typical imaging appearances of run-of-the-mill meningiomas.

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
  • displacement of calcified pineal gland/choroid plexus due to mass effect
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 (5%) 23
    • 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 tumours, but should make one suspect alternative pathology (e.g. haemangiopericytoma or metastasis) {ref needed}
MRI

As is the case with most other intracranial pathology, MRI is the investigation of choice for the diagnosis and characterisation of meningiomas. When appearance and location is typical, the diagnosis can be made with a very high degree of certainty. In some instances, however, the appearances are atypical and careful interpretation is needed to make a correct preoperative diagnosis.

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

Signal characteristics of typical meningiomas include:

  • T1
    • usually isointense to grey matter (60-90%) 3,8, 13
    • hypointense to grey matter (10-40%): particularly fibrous, psammomatous variants
  • T1 C+ (Gd): usually intense and homogeneous enhancement
  • T2
    • usually isointense to grey matter (~50%) 3,8,13
    • hyperintense to grey matter (35-40%)
    • hypointense to grey matter (10-15%): compared to grey matter and usually correlates with harder texture and more fibrous and calcified contents
  • DWI/ADC: 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 tumour
    • absent or significantly reduced N-acetylaspartate (NAA): non-neuronal origin
    • absent or significantly reduced creatine (Cr)
  • MR perfusion:  good correlation between volume transfer constant (k-trans) and histological grade {ref needed}
Helpful imaging signs

A number of helpful imaging signs have been described, including:

  • 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
  • arterial narrowing
    • typically seen in meningiomas which encase arteries
    • useful sign in parasellar tumours, in distinguishing a meningioma from a pituitary macroadenoma; the later typically does not narrow vessels
Oedema

More than half of the meningiomas demonstrate variable amount of vasogenic oedema in adjacent brain parenchyma 24. Correlation between age, gender, tumour size, rapid growth, location (convexity and parasagittal > elsewhere), histologic type, and invasion in the case of malignant meningiomas has been suggested in literature but not yet confirmed. Although in general the presence of severe adjacent oedema considered more compatible with aggressive meningiomas, in some histologically benign types such as secretory type, oedema can be disproportionately larger than the small tumour size.

The underlying mechanism is most likely multifactorial however it has been shown that there is a strong association between the presence and severity of the peritumoral vasogenic oedema (i.e. oedema index) and expression of the vascular endothelial growth factor (VEGF) or expression of CEA and CK 17,25.

List of some of the proposed underlying mechanisms are:

  • venous stasis/occlusion/thrombosis
  • compressive ischaemia
  • aggressive growth/invasion
  • parasitisation of pial vessels
  • histologic subtype: secretory meningioma  25
  • vascular endothelial growth factor (VEGF): produced within the meningioma and enters the adjacent parenchyma
  • expression of CEA and CK
Angiography (DSA)

Catheter angiography is rarely now of diagnostic use, but rather is performed for preoperative embolisation to reduce intraoperative blood loss and alleviate resection of the tumour. This is especially useful for skull base tumours, or those thought to be particularly vascular (e.g. microcystic variants or those with very large vessels). Particles are favoured typically 7-9 days prior to surgery although there are not free of complication particularly one study showed high prevalence of complications associated with particles smaller than 45–150 μm, so risks and benefits should be thoroughly assessed 26.

Meningiomas can have dual blood supply. The majority of tumours are predominantly supplied by meningeal vessels; these are responsible for the sunburst or spokewheel pattern observed on MRI/DSA. Some tumours also have significant pial supply to the periphery of the tumour. {ref needed}

A well known angiographic sign of meningiomas is the mother-in-law sign, in which the tumour contrast blush "comes early, stays late, and is very dense".

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 9,23.

Differential diagnosis

The differential diagnosis generally includes other dural masses as well as some location specific entities.

The main dural masses to consider include:

Specific location differentials include:

In the setting of hyperostosis consider:


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Article Information

rID: 1659
Section: Pathology
Synonyms or Alternate Spellings:
  • Meningiomas
  • Meningioma - general
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    Figure 1: gross pathology
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    Case 1: with trancalvarial spread
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    Figure 2: histology - meningothelial meningioma on smear
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    Case 2: cerebellopontine angle meningioma
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    Figure 3: histology - psammomatous meninigoma
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    Case 3: cystic meningioma
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    Case 4: radiation induced meningiomas
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    Case 5: intraventricular meningioma
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    Case 6: malignant meningioma
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    Case 7: clival meningioma
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    Case 8: with bony invasion
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    Case 9: with spokewheel appearance
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    Case 10: psammomatous meningioma
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    Case 11: calcified meningioma
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    Case 12: falcine meningioma
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    Case 13: pineal region meningioma
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    Case 14: meningioma of craniovertebral junction
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    Case 15: planum sphenoidale meningioma
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    Case 16: clinoid meningioma
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    Case 17: CPA meningioma
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    Case 18: typical sphenoid wing
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    Case 19: olfactory meningioma
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    Case 20: planum sphenoidale meningioma
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    Case 21: suprasellar meningioma
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    Case 22: tuberculum sellae meningioma
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    Case 23: sphenoid ridge meningioma
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    Case 24: psammomatous type
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    Case 25: anaplastic meningioma
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    Case 26: posterior fossa
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    Case 27: showing restricted diffusion
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    Case 28: hypodense
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    Case 29: sphenoid wing meningioma
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     Case 30: CPA meningioma
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    Case 31: olfactory groove meningioma
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    Case 32: fibroblastic type
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    Case 33: atypical meningioma
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    Case 34: meningioma with sigmoid SVT
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    Case 35: invasion into the superior sagittal sinus
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    Case 36: posterior falcine
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    Case 37: posterior fossa atypical meningioma
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    Case 38: with midline shift
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    Case 39: multiple meningiomas
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    Case 40: malignant meningioma
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    Case 41: atypical meningioma
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    Case 42: with cavernous sinus involvement
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    Case 43: causing proptosis
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    Case 44: convexity parietal meningioma
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    Case 45: suprasellar meningioma
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    Case 47: sphenoid wing
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    Case 46: malignant meningioma
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    Case 48: CPA meningioma
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