Atypical meningioma
- Radiopaedia Australia Pty Ltd and Radiopaedia Events Pty Ltd, Director, Founder and CEO (Radiopaedia) (ongoing)
- Biogen Australia Pty Ltd, Investigator-Initiated Research Grant for CAD software in multiple sclerosis: finished Oct 2021 (past)
Updates to Article Attributes
Atypical meningioma refers to a more aggressive form of meningioma and denotes a WHO grade 2 tumour (along with two histological variants, clear cell meningioma and chordoid meningioma). Atypical meningiomas account for 20-30% of all meningiomas 1,2.
It should be noted that epidemiology, clinical presentation, and radiographic features do not reliably distinguish grade 1 (benign) from grade 2 (atypical) meningiomas, and thus they are not unnecessarily repeated here. Generally, these tumours grow faster, have more heterogeneous/aggressive imaging appearances, and have a tendency to recur early.
Terminology
The use of the word "atypical" to denote a higher grade, refers to the histological appearances (see below). However, itThis is perhaps unfavourableunfortunate as it causescan cause confusion for many otheramong clinicians who are used to refer to something being 'atypical' to indicate thatwhen it doesn't look like the 'usual' garden-variety tumour/condition. One should therefore not confuse "atypical meningioma" with histological variants, many of which have unusual imaging and histological features but are nonetheless WHO grade 1 tumours (see meningioma article for further discussion of histological variants).
Pathology
Atypical (WHO grade 2) meningiomas are characterised histologically by 1,2:
- 4 to 19 mitoses per ten high-power fields
- 3 or more of the following 5 histologic features:
- necrosis
- sheet-like growth
- small cell change
- increased cellularity
- prominent nucleoli
- direct invasion of brain parenchyma
It is important to note when reading older literature, that it is only since the WHO 2016 classification, that infiltration into brain parenchymainvasion of an otherwise "benign" grade I1 tumour washas only been sufficient to designate it a grade II2 tumour in more recent WHO classifications 2. Furthermore, this feature remains somewhat controversial due to the lack of consistent sampling of the adjacent brain when samples are sent for histological assessment. In the 5th edition of the WHO classification (2021) this criteria explicitly requires tumour breaching the pia mater and not merely indenting the brain or extending along perivascular spaces 7.
Radiographic features
Generally, it is impossible to confidently distinguishdistinguish between benign (WHO grade 1) from atypical (WHO grade 2) and anaplastic (WHO grade 3) meningiomas with any confidence based on general morphology. The most reliable feature is the presence of lower apparent diffusion coefficient values (reflecting higher cellularity) 3,4.
Importantly, the presence of vasogenic oedema in adjacent brain parenchyma is not a predictor of atypical or anaplastic histology 3.
Brain invasion, although by definition denoting at least a grade II tumour, is also surprisingly difficult to predict on MRI.
Treatment and prognosis
First-line therapy is surgical resection, with radiotherapy (external beam or brachytherapy) often added both to complete and incomplete resections (see Simpson grade). Radiation has been shown to improve local control and prolongs overall survival 6.
No effective chemotherapeutic agents have been identified 5.
The five-year recurrence rate is significantly higher (41%) than that seen in grade 1 (benign) meningiomas (12%) 3.
-<p><strong>Atypical meningioma</strong> refers to a more aggressive form of <a href="/articles/meningioma">meningioma</a> and denotes a WHO grade 2 tumour (along with two histological variants, <a href="/articles/clear-cell-meningioma">clear cell meningioma</a> and <a href="/articles/chordoid-meningioma">chordoid meningioma</a>). Atypical meningiomas account for 20-30% of all meningiomas <sup>1,2</sup>. </p><p>It should be noted that epidemiology, clinical presentation, and radiographic features do not reliably distinguish grade 1 (benign) from grade 2 (atypical) <a href="/articles/meningioma">meningiomas</a>, and thus they are not unnecessarily repeated here. Generally, these tumours grow faster, have more heterogeneous/aggressive imaging appearances, and have a tendency to recur early. </p><h4>Terminology</h4><p>The use of the word "atypical" to denote a higher grade, refers to the histological appearances (see below). However, it is perhaps unfavourable as it causes confusion for many other clinicians who are used to refer to something being 'atypical' to indicate that it doesn't look like the 'usual' garden-variety tumour/condition. One should therefore not confuse "atypical meningioma" with histological variants, many of which have unusual imaging and histological features but are nonetheless WHO grade 1 tumours (see <a href="/articles/meningioma">meningioma</a> article for further discussion of histological variants). </p><h4>Pathology</h4><p>Atypical (WHO grade 2) meningiomas are characterised histologically by <sup>1,2</sup>: </p><ul>- +<p><strong>Atypical meningioma</strong> refers to a more aggressive form of <a href="/articles/meningioma">meningioma</a> and denotes a WHO grade 2 tumour (along with two histological variants, <a href="/articles/clear-cell-meningioma">clear cell meningioma</a> and <a href="/articles/chordoid-meningioma">chordoid meningioma</a>). Atypical meningiomas account for 20-30% of all meningiomas <sup>1,2</sup>. </p><p>It should be noted that epidemiology, clinical presentation, and radiographic features do not reliably distinguish grade 1 (benign) from grade 2 (atypical) <a href="/articles/meningioma">meningiomas</a>, and thus they are not unnecessarily repeated here. Generally, these tumours grow faster, have more heterogeneous/aggressive imaging appearances, and have a tendency to recur early. </p><h4>Terminology</h4><p>The use of the word "atypical" to denote a higher grade, refers to the histological appearances (see below). This is perhaps unfortunate as it can cause confusion among clinicians who are used to refer to something being 'atypical' when it doesn't look like the 'usual' garden-variety tumour/condition. One should therefore not confuse "atypical meningioma" with histological variants, many of which have unusual imaging and histological features but are nonetheless WHO grade 1 tumours (see <a href="/articles/meningioma">meningioma</a> article for further discussion of histological variants). </p><h4>Pathology</h4><p>Atypical (WHO grade 2) meningiomas are characterised histologically by <sup>1,2</sup>: </p><ul>
-</ul><p>It is important to note when reading older literature, that it is only since the WHO 2016 classification, that infiltration into brain parenchyma of an otherwise "benign" grade I tumour was sufficient to designate it a grade II tumour <sup>2</sup>.</p><h4>Radiographic features</h4><p>Generally, it is impossible to confidently distinguish benign (WHO grade 1) from atypical (WHO grade 2) and anaplastic (WHO grade 3) meningiomas based on general morphology. The most reliable feature is the presence of lower <a href="/articles/apparent-diffusion-coefficient-1">apparent diffusion coefficient</a> values (reflecting higher cellularity) <sup>3,4</sup>.</p><p>Importantly, the presence of vasogenic oedema in adjacent brain parenchyma is not a predictor of atypical or anaplastic histology <sup>3</sup>. </p><p>Brain invasion, although by definition denoting at least a grade II tumour, is also surprisingly difficult to predict on MRI. </p><h4>Treatment and prognosis</h4><p>First-line therapy is surgical resection, with radiotherapy (external beam or <a href="/articles/brachytherapy">brachytherapy</a>) often added both to complete and incomplete resections (see <a href="/articles/simpson-grade">Simpson grade</a>). Radiation has been shown to improve local control and prolongs overall survival <sup>6</sup>. </p><p>No effective chemotherapeutic agents have been identified <sup>5</sup>. </p><p>The five-year recurrence rate is significantly higher (41%) than that seen in grade 1 (benign) meningiomas (12%) <sup>3</sup>. </p>- +</ul><p>It is important to note when reading older literature, that brain invasion of an otherwise "benign" grade 1 tumour has only been sufficient to designate it a grade 2 tumour in more recent WHO classifications <sup>2</sup>. Furthermore, this feature remains somewhat controversial due to the lack of consistent sampling of the adjacent brain when samples are sent for histological assessment. In the 5<sup>th</sup> edition of the WHO classification (2021) this criteria explicitly requires tumour breaching the pia mater and not merely indenting the brain or extending along perivascular spaces <sup>7</sup>.</p><h4>Radiographic features</h4><p>Generally, it is impossible to distinguish between benign (WHO grade 1) from atypical (WHO grade 2) and anaplastic (WHO grade 3) meningiomas with any confidence based on general morphology. The most reliable feature is the presence of lower <a href="/articles/apparent-diffusion-coefficient-1">apparent diffusion coefficient</a> values (reflecting higher cellularity) <sup>3,4</sup>.</p><p>Importantly, the presence of vasogenic oedema in adjacent brain parenchyma is not a predictor of atypical or anaplastic histology <sup>3</sup>. </p><p>Brain invasion, although by definition denoting at least a grade II tumour, is also surprisingly difficult to predict on MRI. </p><h4>Treatment and prognosis</h4><p>First-line therapy is surgical resection, with radiotherapy (external beam or <a href="/articles/brachytherapy">brachytherapy</a>) often added both to complete and incomplete resections (see <a href="/articles/simpson-grade">Simpson grade</a>). Radiation has been shown to improve local control and prolongs overall survival <sup>6</sup>. </p><p>No effective chemotherapeutic agents have been identified <sup>5</sup>. </p><p>The five-year recurrence rate is significantly higher (41%) than that seen in grade 1 (benign) meningiomas (12%) <sup>3</sup>. </p>
References changed:
- 7. Sahm F, Perry A, von Deimling A, Claus EB, Mawrin C, Brastianos PK, Santagata S, Meningioma. In: WHO Classification of Tumours Editorial Board. Central nervous system tumours. Lyon (France): International Agency for Research on Cancer; 2021. (WHO classification of tumours series, 5th ed.; vol. 6). <a href="https://publications.iarc.fr/601.">https://publications.iarc.fr/601</a>
Unable to process the form. Check for errors and try again.