Meningioma

Meningioma is the most common type of extra-axial neoplasm and account for 14 - 20% of all intracranial neoplasms ⁴. They originate from the arachnoid cap cells of the meninges.

Demographics and clinical presentation

Meningiomas are more common in women, with a ratio of 2:1 intracranially and 4:1 in the spine. They are uncommon in patients before the age of 40 and should raise suspicion of NF2 when found in young patients.

Most common presentations include ⁸:

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

Pathology and classification

Although the majority of tumours are sporadic, they are also seen in the setting of previous cranial irradiation and of course in patients with NF2 (Merlin gene Chromosome 22). Additionally meningiomas demonstrate oestrogen sensitivity and may grow during pregnancy. 

They are also divided histologically into ^3,8:

1. meningothelial
2. fibroblastic : abundant reticulum and 'stout' collagen
3. transitional : whorl formation
4. syncytial : poorly formed polygonal cells arranged in lobules
5. angioblastic : now classified separately as a haemangiopericytoma
6. clear cell meningioma:  high rate of local recurrence ⁶
7. psammomatous
8. microcystic
9. secretory
10. chordoid
11. lymphoplasmacyte-rich
12. metaplastic
13. papillary: high rate of local recurrence ⁸
14. mixed type

Macroscopic

• 2 forms : Globose and en plaque
• rounded, well defined dural mass
• surface typically encapsulated with thin fibrous tissue

Microscopic

• arise from meningothelial arachnoid cells
• histologic subtypes
  • transitional
  • fibroblastic
  • syncytial
  • psammomatous (see case 8)
  • secretory
  • microcytic
  • papillary and rhabdoid have a propensity to recur
• hemangiopericytoma (CNS) : previously angioblastic subtype

Variants

• intraosseous meningioma : sclerotic or lucent
• degeneration into : (rare)
  • cystic meningioma
  • osteoblastic meningioma
  • chondromatoud meningioma
  • sarcomatous degeneration
  • fatty degeneration
• intraventricular meningiomas
• atypical meningiomas (WHO II) : have increased mitotic rate, only make up approximately 7.2% of all meningiomas ⁴, but have a greater tendency to recur. They generally have more restricted diffusion on DWI.
• malignant meningiomas (WHO III) : uncommon accounting for only 2.4% of all meningiomas ⁴, and demonstrate intraparenchymal invasion, rapid growth, and a high mitotic rate or sarcomatous degeneration. Like atypical meningiomas they too demonstrate restricted diffusion on DWI. They are thought to originally be standard meningiomas which undergo malignant degeneration. The papillary sub type appears to do so more frequently than others.
• radiation induced meningiomas : more frequently multiple, and typically occur 35 years or so after radiotherapy. Meningiomas are a much more frequent complication of radiotherapy compared to sarcomas or gliomas.
• clear cell meningioma: Have up to a 60% recurrence rate and occur in younger patients ⁶

Grading

Generally follows the WHO classification for CNS tumours ⁷:

• WHO I : meningioma
• WHO II : atypical meningioma
• WHO III : malignant meningioma

There is also a Simpson grade for meningiomas.

Site

• 85 - 90% supratentorial ⁸
  • 45% parasagittal, convexities
  • 15 - 20% sphenoid ridge
  • 10% olfactory groove / planum sphenoidale (case 6)
  • 5 - 10% juxtasellar
• 5 - 10% infratentorial
• < 5% miscellaneous intracranial
  • intraventricular
  • optic nerve
  • pineal gland
  • intraspinal - especially thoracic
• <1% "extra dural"
  • sinonasal cavity - most common
  • intraosseous and may involve scalp
  • parotid gland
  • skin

Radiographic features

Plain film 

• enlarged menigeal artery grooves
• hyperostosis or lytic regions
• calcification

CT

• 60% slightly hyperdense to normal brain
• 20 - 30% have some calcification ⁸
• 72% brightly and homogenously contrast enhance ⁸, less frequent in malignant or cystic variants
• hyperostosis
  • typical for meningiomas that abut the base of skull
  • need to distinguish reactive hyperostosis from skull vault invasion (eventually involves the outer table too)
  lytic regions

MRI

• T1 :
  • iso intense : ~ 60 - 65% ^3,8
  • hypo intense : ~ 35 - 40% compared to grey matter
  • enhancement : usually intense and homogenous
• T1 C+ (GAD) : usually intense and homogenous enhancement
• T2
  • iso intense : ~50% ^3,8
  • hyper intense : ~35-40%
  • hypo intense : ~10-15% compared to grey matter
• CSF cleft sign
• dural tail seen in 60 - 72% ² (note that a dural tail is also seen in other processes)

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

Oedema can be seen and correlates with:

• size
• rapid growth
• location (convexity and parasagittal > elsewhere)
• invasion in the case of malignant meningiomas

The underlying mechansims for the oedema may relate to:

• venous stasis / occlusion / thrombosis
• compressive ischaemia
• aggressive growth / invasion
• parasitisation or pial vessles

MRS

Usually MRS does not play a significant role in diagnosis. Nonetheless certain features are present:

• increase in alanine (1.3 - 1.5ppm)
• absent N-acetylaspartate
• no glutamine

 MRI Perfusion

• good correlation between volume transfer constant (k-trans) and histological grade

Angiography

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

Differential diagnoses

The differential diagnosis largely depends on location:

• cerebellopontine angle
  • acoustic schwannoma
• parasellar region
  • pituitary macroadenoma
  • craniopharyngioma
• elsewhere
  • haemangiopericytoma
  • granuloma
    • sarcoidosis
    • tuberculosis
  • idiopathic hypertrophic pachymeningitis
  • extramedullary haematopoeisis
  • chondrosarcoma
  • chordoma

In the setting of hyperostosis:

• Paget disease
• fibrous dysplasia

In the setting of lucent intraossous meningioma : solitary lucent lesion of the skull

Complications

• depends on location:
  • sinus invasion / thrombosis
  • vascularity
  • intracranial oedema : secondary to compressive ischaemia, venous stasis, aggressive growth, parasitzation of pial vessels
  • intraosseous extension : may be hyperostotic or osteolytic

Treatment and prognosis

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

Recurrence rate varies with grade and length of followup ⁸

• WHO I - meningioma : 6.9%
• WHO II - atypical meningioma : 34.6%
• WHO III - malignant meningioma : 72.7%

• 5 year followup : 5%
• 10 year followup : 5%
• 32 year followup : 5%

Metastatic disease is rare, but has been reported ⁸.