Olfactory groove meningioma
50 years old female.
Meningiomas are the most common extra-axial tumours of the central nervous system and account for 14-20% of all intracranial neoplasms 4. They are a non-glial neoplasm that originates from the arachnoid cap cells of the meninges.
This article is a general discussion of meningiomas, and focuses on the imaging findings of intracranial disease. For spinal disease refer to spinal meningioma.
Meningiomas are more common in women, with a ratio of 2:1 intracranially and 4:1 inthe spine. They are uncommon in patients before the age of 40 and should raise suspicion of neurofibromatosis type 2 (NF2) when found in young patients.
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%
• focal neurological deficits
Meningiomas may also become clinically apparent due to complications dependent on location including:
• 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)
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 demonstrateoestrogen sensitivity and may grow during pregnancy.
They are also divided histologically into 3,8:
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 - high rate of local recurrence 6
8. microcystic 12
13. papillary : has a high rate of local recurrence 8
14. mixed type
In general there are two main macroscopic forms: globose and en plaque.
Globose are rounded, well defined dural masses, likened to the appearance of a fried egg seen in profile.
En plaque meningiomas on the other hand are extensive regions of dural thickening.
• arise from meningothelial arachnoid cells
• histological sub types include
o papillary and rhabdoid : have a propensity to recur
• haemangiopericytoma (CNS) : previously angioblastic sub type
• intraosseous meningioma : sclerotic or lucent
• degeneration into : (rare)
o cystic meningioma
o osteoblastic meningioma
o chondromatoid meningioma
o meningioma with sarcomatous degeneration
o meningioma with fatty degeneration
• intraventricular meningioma
• atypical meningioma (WHO II) - have an increased mitotic rate, only make up approximately 7% of all meningiomas 4, but have a greater tendency to recur. They generally have more restricted diffusion on DWI.
• malignant meningioma (WHO III)
o uncommon accounting for only 2.4% of all meningiomas 4, and demonstrateintraparenchymal invasion, rapid growth, and a high mitotic rate or sarcomatous degeneration.
o like atypical meningiomas they too demonstrate restricted diffusion on DWI.
o they are thought to originally be standard meningiomas which undergo malignant degeneration.
o the papillary sub type appears to do so more frequently than others.
• radiation induced meningioma :
o more frequently multiple, and typically occur ~ 35 years after radiotherapy.
o 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
• microcystic meningioma : rare, and are typically very high on T2 weighted imagingand are more commonly associated with atypical features and adjacent brainoedema 12
Generally follows the WHO classification for CNS tumours 7,11:
• WHO I - meningioma : ~ 88-95 %
• WHO II - atypical meningioma (atypical, clear cell, chordoid) : ~ 5-6 %
• WHO III - malignant meningioma (rhabdoid, anaplastic, papillary) : ~ 1 %
• WHO IV - meningioma with sarcomatous degeneration : extremely rare 11
There is also a Simpson grade for meningiomas.
Meningiomas are located anywhere that meninges are found, and in some places where only rest cells are presumed to be located. Locations include:
• 85-90% supratentorial 8
o 45% parasagittal, convexities
o 15-20% sphenoid ridge
o 10% olfactory groove / planum sphenoidale
o 5-10% juxtasellar
• 5-10% infratentorial
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