Schwannoma
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Schwannomas, less commonly called neurinomas or neurilemmomas, are benign tumours of Schwann cell origin and are the most common tumour of peripheral nerves, including cranial nerves.
This article provides a general overview of schwannomas. For a discussion of schwannomas located at specific sites, please refer to the relevant articles listed below.
Epidemiology
The vast majority of schwannomas are sporadic, with a peak presentation in the 5th to 6th decades. There is no sex predilection 9.
When they occur in patients with neurofibromatosis type 2 (NF2), schwannomas usually present by the 3rd decade 4.
Associations
Most schwannomas are solitary (90%) 2,9 and sporadic, however, there is an association with neurofibromatosis type 2 (NF2) (abnormality of chromosome 22). Multiple schwannomas are characteristic of neurofibromatosis type 2. Approximately 18% of solitary schwannomas occur in patients with neurofibromatosis type 2 4.
There is also schwannomatosis, which consists ofmultiple schwannomas without the concomitant involvement of cranial nerve VIII.
Clinical presentation
Presentation depends on the location of the tumour (see below) but generally, symptoms are due to local mass effect or dysfunction of the nerve they arise from.
Pathology
Location
-
intracranial schwannomas
- cranial nerves: although almost any cranial nerve may be involved, except olfactory nerves and optic nerves which lack sheaths composed of Schwann cells, by far the most commonly involved nerve is the vestibulocochlear nerve (CN VIII)
- non-cranial nerve or intracerebral (very rare)
- intraorbital schwannoma: commonly arise from supraorbital and supratrochlear nerves in the upper anterior orbital cavity 10
-
spinal schwannoma
- arising from spinal nerve roots
- trunk
- intercostal nerves: see intercostal nerve schwannoma
- posterior mediastinum
- retroperitoneum
- gastrointestinal schwannoma
- limbs
- especially flexor surfaces (specifically ulnar and peroneal nerves)
Macroscopic appearance
Schwannomas are benign encapsulated neoplasms of Schwann cells (WHO grade 1 9). They arise eccentrically from their parent nerve, with the nerve fibres splayed along their surface (as distinct to neurofibromas which arise within the nerve).
Microscopic appearance
Conventional schwannomas are composed of spindle cells that demonstrate two growth patterns: Antoni type A and Antoni type B 7-9.
Antoni type A pattern: elongated cells are thickly bundled and organised in fascicles. Palisades are occasionally observed; when they are prominent they constitute Verocay bodies. The cells also have fusiform nuclei and eosinophilic cytoplasm. Antoni type A is a strongly Periodic acid-Schiff (PAS) positive and immunoperoxidase assay for laminin 10.
Antoni type B pattern cells are less compact and are prone to cystic degeneration, and haphazardly distributed cells with distinct cytoplasmic margins in a loose myxoid matrix 10.
Subtypes
Several schwannoma subtypes are recognised 6,8,9:
-
ancient schwannoma
- degenerative changes with hyalinization, ischaemic change, and atypical appearing nuclei
- cellular schwannoma
- predominantly composed of Antoni type A tissue
- no Verocay bodies
- most commonly found arising from large nerves, brachial and lumbosacral plexus and thus often in a paravertebral location
- epithelioid schwannoma
- usually sporadic but may be associated with schwannomatosis
- microcystic/reticular schwannoma
- rarest subtype
- typically arise from viscera, especially the gastrointestinal tract 9
-
plexiform schwannoma
- usually arise from skin or subcutaneous tissues
- usually diagnosed at birth or childhood
- usually sporadic, but rarely associated with neurofibromatosis type 2
- should not be confused with plexiform neurofibromas
- associated with neurofibromatosis type 1
- may undergo malignant change
- neuroblastoma type 10
- schwannoma with neuromelanin accumulation
- not a distinct subtype
- not to be confused with PRKAR1A-associated malignant melanotic nerve sheath tumour (a.k.a. melanotic schwannoma) seen in patients with Carney complex 9
Radiographic features
General imaging features of schwannomas include:
- well-circumscribed masses which displace adjacent structures without direct invasion
- cystic and fatty degeneration is common 4
- the larger a schwannoma, the more likely it is to show heterogeneity because of cystic degeneration or haemorrhage 3
- haemorrhage occurs in 5% of cases 3
- calcification is rare
CT
CT is not as sensitive or specific for the diagnosis of schwannoma as MRI but is often the first investigation obtained. It is particularly useful in assessing bony changes adjacent to the tumour.
Imaging features include:
- low to intermediate attenuation
- intense contrast enhancement
- small tumours typically demonstrate homogeneous enhancement
- larger tumours may show heterogeneous enhancement
- adjacent bone remodelling with smooth corticated edges
MRI
Schwannomas have fairly predictable signal characteristics 7:
- T1: isointense or hypointense
- T1 C+ (Gd): intense enhancement
-
T2: heterogeneously hyperintense (Antoni type A: relatively low; Antoni type B: high)
- cystic degenerative areas may be present, especially in larger tumours
- T2*: larger tumours often have areas of haemosiderin
Several signs can also be useful:
- split-fat sign: the thin peripheral rim of fat best seen on planes along the long axis of the lesion in non-fat-suppressed sequences
-
target sign
- peripheral high T2 signal
- central low signal
- rarely seen intracranially 7
- fascicular sign: multiple small ring-like structures
Treatment and prognosis
Schwannomas are slow-growing lesions. Surgery is the treatment of choice. As schwannomas do not infiltrate the parent nerve, they can usually be separated from it. Recurrence is unusual after complete resection. They rarely undergo malignant change.
-<p><strong>Schwannomas</strong>, less commonly called <strong>neurinomas </strong>or <strong>neurilemmomas</strong>, are benign tumours of Schwann cell origin and are the most common tumour of peripheral nerves, including cranial nerves. </p><p>This article provides a general overview of schwannomas. For a discussion of schwannomas located at specific sites, please refer to the relevant articles listed below.</p><h4>Epidemiology</h4><p>The vast majority of schwannomas are sporadic, with a peak presentation in the 5<sup>th </sup>to 6<sup>th</sup> decades. There is no sex predilection <sup>9</sup>.</p><p>When they occur in patients with <a href="/articles/neurofibromatosis-type-2-3">neurofibromatosis type 2 (NF2)</a>, schwannomas usually present by the 3<sup>rd</sup> decade <sup>4</sup>. </p><h5>Associations</h5><p>Most schwannomas are solitary (90%) <sup>2,9</sup> and sporadic, however, there is an association with <a href="/articles/neurofibromatosis-type-2-3">neurofibromatosis type 2 (NF2)</a> (abnormality of chromosome 22). Multiple schwannomas are characteristic of neurofibromatosis type 2. Approximately 18% of solitary schwannomas occur in patients with neurofibromatosis type 2 <sup>4</sup>.</p><p>There is also <a href="/articles/schwannomatosis">schwannomatosis</a>, which consists of<strong> </strong>multiple schwannomas without the concomitant involvement of cranial nerve VIII.</p><h4>Clinical presentation</h4><p>Presentation depends on the location of the tumour (see below) but generally, symptoms are due to local mass effect or dysfunction of the nerve they arise from. </p><h4>Pathology</h4><h5>Location</h5><ul>-<li>-<a href="/articles/intracranial-schwannoma">intracranial schwannomas</a><ul>-<li>cranial nerves: although almost any cranial nerve may be involved, except olfactory nerves and optic nerves which lack sheaths composed of Schwann cells, by far the most commonly involved nerve is the <a href="/articles/vestibulocochlear-nerve">vestibulocochlear nerve (CN VIII)</a> </li>-<li>non-cranial nerve or intracerebral (very rare) </li>-</ul>-</li>-<li>intraorbital schwannoma: commonly arise from supraorbital and supratrochlear nerves in the upper anterior orbital cavity <sup>10</sup>-</li>-<li>-<a href="/articles/spinal-schwannoma">spinal schwannoma</a><ul><li>arising from <a href="/articles/spinal-schwannoma">spinal nerve roots</a>-</li></ul>-</li>-<li>trunk<ul>-<li>-<a href="/articles/intercostal-nerve">intercostal nerves</a>: see <a href="/articles/intercostal-nerve-neurilemmoma">intercostal nerve schwannoma</a>-</li>-<li>posterior mediastinum</li>-<li>retroperitoneum</li>-<li><a href="/articles/gastrointestinal-schwannoma">gastrointestinal schwannoma</a></li>-</ul>-</li>-<li>limbs<ul><li>especially flexor surfaces (specifically ulnar and peroneal nerves)</li></ul>-</li>-</ul><h5>Macroscopic appearance</h5><p>Schwannomas are benign encapsulated neoplasms of Schwann cells (WHO grade 1 <sup>9</sup>). They arise eccentrically from their parent nerve, with the nerve fibres splayed along their surface (as distinct to <a href="/articles/neurofibroma">neurofibromas</a> which arise within the nerve).</p><h5>Microscopic appearance</h5><p>Conventional schwannomas are composed of spindle cells that demonstrate two growth patterns: Antoni type A and Antoni type B <sup>7-9</sup>.</p><p>Antoni type A pattern: elongated cells are thickly bundled and organised in fascicles. Palisades are occasionally observed; when they are prominent they constitute <a href="/articles/verocay-bodies">Verocay bodies</a>. The cells also have fusiform nuclei and eosinophilic cytoplasm. Antoni type A is a strongly Periodic acid-Schiff (PAS) positive and immunoperoxidase assay for laminin <sup>10</sup>.</p><p>Antoni type B pattern cells are less compact and are prone to cystic degeneration, and haphazardly distributed cells with distinct cytoplasmic margins in a loose myxoid matrix <sup>10</sup>.</p><h5>Subtypes</h5><p>Several schwannoma subtypes are recognised <sup>6,8,9</sup>:</p><ul>-<li>-<a href="/articles/ancient-schwannoma">ancient schwannoma</a><ul><li>degenerative changes with hyalinization, ischaemic change, and atypical appearing nuclei</li></ul>-</li>-<li>cellular schwannoma<ul>-<li>predominantly composed of Antoni type A tissue</li>-<li>no Verocay bodies</li>-<li>most commonly found arising from large nerves, brachial and lumbosacral plexus and thus often in a paravertebral location</li>-</ul>-</li>-<li>epithelioid schwannoma<ul><li>usually sporadic but may be associated with schwannomatosis</li></ul>-</li>-<li>microcystic/reticular schwannoma<ul>-<li>rarest subtype</li>-<li>typically arise from viscera, especially the gastrointestinal tract <sup>9</sup>-</li>-</ul>-</li>-<li>-<a href="/articles/plexiform-schwannoma">plexiform schwannoma</a><ul>-<li>usually arise from skin or subcutaneous tissues</li>-<li>usually diagnosed at birth or childhood</li>-<li>usually sporadic, but rarely associated with <a title="Neurofibromatosis type 2" href="/articles/neurofibromatosis-type-2-3">neurofibromatosis type 2</a>-</li>-<li>should not be confused with <a href="/articles/plexiform-neurofibroma">plexiform neurofibromas</a><ul>-<li>associated with <a href="/articles/neurofibromatosis-type-1">neurofibromatosis type 1</a>-</li>-<li>may undergo malignant change</li>-</ul>-</li>-</ul>-</li>-<li>neuroblastoma type <sup>10</sup>-</li>-<li>schwannoma with neuromelanin accumulation<ul>-<li>not a distinct subtype</li>-<li>not to be confused with <a title="PRKAR1A-associated malignant melanotic nerve sheath tumor" href="/articles/prkar1a-associated-malignant-melanotic-nerve-sheath-tumor">PRKAR1A-associated malignant melanotic nerve sheath tumour</a> (a.k.a. melanotic schwannoma) seen in patients with <a href="/articles/carney-complex">Carney complex</a> <sup>9 </sup>-</li>-</ul>-</li>-</ul><h4>Radiographic features</h4><p>General imaging features of schwannomas include:</p><ul>-<li>well-circumscribed masses which displace adjacent structures without direct invasion</li>-<li>cystic and fatty degeneration is common <sup>4</sup>-</li>-<li>the larger a schwannoma, the more likely it is to show heterogeneity because of cystic degeneration or haemorrhage <sup>3</sup>-</li>-<li>haemorrhage occurs in 5% of cases <sup>3</sup>-</li>-<li>calcification is rare</li>-</ul><h5>CT</h5><p>CT is not as sensitive or specific for the diagnosis of schwannoma as MRI but is often the first investigation obtained. It is particularly useful in assessing bony changes adjacent to the tumour. </p><p>Imaging features include: </p><ul>-<li>low to intermediate attenuation</li>-<li>intense contrast enhancement<ul>-<li>small tumours typically demonstrate homogeneous enhancement</li>-<li>larger tumours may show heterogeneous enhancement</li>-</ul>-</li>-<li>adjacent bone remodelling with smooth corticated edges</li>-</ul><h5>MRI</h5><p>Schwannomas have fairly predictable signal characteristics <sup>7</sup>:</p><ul>-<li>-<strong>T1:</strong> isointense or hypointense</li>-<li>-<strong>T1 C+ (Gd):</strong> intense enhancement</li>-<li>-<strong>T2:</strong> heterogeneously hyperintense (Antoni type A: relatively low; Antoni type B: high)<ul><li>cystic degenerative areas may be present, especially in larger tumours</li></ul>-</li>-<li>-<strong>T2*:</strong> larger tumours often have areas of haemosiderin</li>-</ul><p>Several signs can also be useful:</p><ul>-<li>-<a href="/articles/split-fat-sign">split-fat sign</a>: the thin peripheral rim of fat best seen on planes along the long axis of the lesion in non-fat-suppressed sequences</li>-<li>-<a href="/articles/target-sign-disambiguation">target sign</a><ul>-<li>peripheral high T2 signal</li>-<li>central low signal</li>-<li>rarely seen intracranially <sup>7</sup>-</li>-</ul>-</li>-<li>-<a href="/articles/fascicular-sign">fascicular sign</a>: multiple small ring-like structures</li>- +<p><strong>Schwannomas</strong>, less commonly called <strong>neurinomas </strong>or <strong>neurilemmomas</strong>, are benign tumours of Schwann cell origin and are the most common tumour of peripheral nerves, including cranial nerves. </p><p>This article provides a general overview of schwannomas. For a discussion of schwannomas located at specific sites, please refer to the relevant articles listed below.</p><h4>Epidemiology</h4><p>The vast majority of schwannomas are sporadic, with a peak presentation in the 5<sup>th </sup>to 6<sup>th</sup> decades. There is no sex predilection <sup>9</sup>.</p><p>When they occur in patients with <a href="/articles/neurofibromatosis-type-2-3">neurofibromatosis type 2 (NF2)</a>, schwannomas usually present by the 3<sup>rd</sup> decade <sup>4</sup>. </p><h5>Associations</h5><p>Most schwannomas are solitary (90%) <sup>2,9</sup> and sporadic, however, there is an association with <a href="/articles/neurofibromatosis-type-2-3">neurofibromatosis type 2 (NF2)</a> (abnormality of chromosome 22). Multiple schwannomas are characteristic of neurofibromatosis type 2. Approximately 18% of solitary schwannomas occur in patients with neurofibromatosis type 2 <sup>4</sup>.</p><p>There is also <a href="/articles/schwannomatosis">schwannomatosis</a>, which consists of<strong> </strong>multiple schwannomas without the concomitant involvement of cranial nerve VIII.</p><h4>Clinical presentation</h4><p>Presentation depends on the location of the tumour (see below) but generally, symptoms are due to local mass effect or dysfunction of the nerve they arise from. </p><h4>Pathology</h4><h5>Location</h5><ul>
- +<li>
- +<a href="/articles/intracranial-schwannoma">intracranial schwannomas</a><ul>
- +<li>cranial nerves: although almost any cranial nerve may be involved, except olfactory nerves and optic nerves which lack sheaths composed of Schwann cells, by far the most commonly involved nerve is the <a href="/articles/vestibulocochlear-nerve">vestibulocochlear nerve (CN VIII)</a> </li>
- +<li>non-cranial nerve or intracerebral (very rare) </li>
- +</ul>
- +</li>
- +<li>intraorbital schwannoma: commonly arise from supraorbital and supratrochlear nerves in the upper anterior orbital cavity <sup>10</sup>
- +</li>
- +<li>
- +<a href="/articles/spinal-schwannoma">spinal schwannoma</a><ul><li>arising from <a href="/articles/spinal-schwannoma">spinal nerve roots</a>
- +</li></ul>
- +</li>
- +<li>trunk<ul>
- +<li>
- +<a href="/articles/intercostal-nerve">intercostal nerves</a>: see <a href="/articles/intercostal-nerve-neurilemmoma">intercostal nerve schwannoma</a>
- +</li>
- +<li>posterior mediastinum</li>
- +<li>retroperitoneum</li>
- +<li><a href="/articles/gastrointestinal-schwannoma">gastrointestinal schwannoma</a></li>
- +</ul>
- +</li>
- +<li>limbs<ul><li>especially flexor surfaces (specifically ulnar and peroneal nerves)</li></ul>
- +</li>
- +</ul><h5>Macroscopic appearance</h5><p>Schwannomas are benign encapsulated neoplasms of Schwann cells (WHO grade 1 <sup>9</sup>). They arise eccentrically from their parent nerve, with the nerve fibres splayed along their surface (as distinct to <a href="/articles/neurofibroma">neurofibromas</a> which arise within the nerve).</p><h5>Microscopic appearance</h5><p>Conventional schwannomas are composed of spindle cells that demonstrate two growth patterns: Antoni type A and Antoni type B <sup>7-9</sup>.</p><p>Antoni type A pattern: elongated cells are thickly bundled and organised in fascicles. Palisades are occasionally observed; when they are prominent they constitute <a href="/articles/verocay-bodies">Verocay bodies</a>. The cells also have fusiform nuclei and eosinophilic cytoplasm. Antoni type A is a strongly Periodic acid-Schiff (PAS) positive and immunoperoxidase assay for laminin <sup>10</sup>.</p><p>Antoni type B pattern cells are less compact and are prone to cystic degeneration, and haphazardly distributed cells with distinct cytoplasmic margins in a loose myxoid matrix <sup>10</sup>.</p><h5>Subtypes</h5><p>Several schwannoma subtypes are recognised <sup>6,8,9</sup>:</p><ul>
- +<li>
- +<a href="/articles/ancient-schwannoma">ancient schwannoma</a><ul><li>degenerative changes with hyalinization, ischaemic change, and atypical appearing nuclei</li></ul>
- +</li>
- +<li>cellular schwannoma<ul>
- +<li>predominantly composed of Antoni type A tissue</li>
- +<li>no Verocay bodies</li>
- +<li>most commonly found arising from large nerves, brachial and lumbosacral plexus and thus often in a paravertebral location</li>
- +</ul>
- +</li>
- +<li>epithelioid schwannoma<ul><li>usually sporadic but may be associated with schwannomatosis</li></ul>
- +</li>
- +<li>microcystic/reticular schwannoma<ul>
- +<li>rarest subtype</li>
- +<li>typically arise from viscera, especially the gastrointestinal tract <sup>9</sup>
- +</li>
- +</ul>
- +</li>
- +<li>
- +<a href="/articles/plexiform-schwannoma">plexiform schwannoma</a><ul>
- +<li>usually arise from skin or subcutaneous tissues</li>
- +<li>usually diagnosed at birth or childhood</li>
- +<li>usually sporadic, but rarely associated with <a title="Neurofibromatosis type 2" href="/articles/neurofibromatosis-type-2-3">neurofibromatosis type 2</a>
- +</li>
- +<li>should not be confused with <a href="/articles/plexiform-neurofibroma">plexiform neurofibromas</a><ul>
- +<li>associated with <a href="/articles/neurofibromatosis-type-1">neurofibromatosis type 1</a>
- +</li>
- +<li>may undergo malignant change</li>
- +</ul>
- +</li>
- +</ul>
- +</li>
- +<li>neuroblastoma type <sup>10</sup>
- +</li>
- +<li>schwannoma with neuromelanin accumulation<ul>
- +<li>not a distinct subtype</li>
- +<li>not to be confused with <a title="PRKAR1A-associated malignant melanotic nerve sheath tumor" href="/articles/prkar1a-associated-malignant-melanotic-nerve-sheath-tumor">PRKAR1A-associated malignant melanotic nerve sheath tumour</a> (a.k.a. melanotic schwannoma) seen in patients with <a href="/articles/carney-complex">Carney complex</a> <sup>9 </sup>
- +</li>
- +</ul>
- +</li>
- +</ul><h4>Radiographic features</h4><p>General imaging features of schwannomas include:</p><ul>
- +<li>well-circumscribed masses which displace adjacent structures without direct invasion</li>
- +<li>cystic and fatty degeneration is common <sup>4</sup>
- +</li>
- +<li>the larger a schwannoma, the more likely it is to show heterogeneity because of cystic degeneration or haemorrhage <sup>3</sup>
- +</li>
- +<li>haemorrhage occurs in 5% of cases <sup>3</sup>
- +</li>
- +<li>calcification is rare</li>
- +</ul><h5>CT</h5><p>CT is not as sensitive or specific for the diagnosis of schwannoma as MRI but is often the first investigation obtained. It is particularly useful in assessing bony changes adjacent to the tumour. </p><p>Imaging features include: </p><ul>
- +<li>low to intermediate attenuation</li>
- +<li>intense contrast enhancement<ul>
- +<li>small tumours typically demonstrate homogeneous enhancement</li>
- +<li>larger tumours may show heterogeneous enhancement</li>
- +</ul>
- +</li>
- +<li>adjacent bone remodelling with smooth corticated edges</li>
- +</ul><h5>MRI</h5><p>Schwannomas have fairly predictable signal characteristics <sup>7</sup>:</p><ul>
- +<li>
- +<strong>T1:</strong> isointense or hypointense</li>
- +<li>
- +<strong>T1 C+ (Gd):</strong> intense enhancement</li>
- +<li>
- +<strong>T2:</strong> heterogeneously hyperintense (Antoni type A: relatively low; Antoni type B: high)<ul><li>cystic degenerative areas may be present, especially in larger tumours</li></ul>
- +</li>
- +<li>
- +<strong>T2*:</strong> larger tumours often have areas of haemosiderin</li>
- +</ul><p>Several signs can also be useful:</p><ul>
- +<li>
- +<a href="/articles/split-fat-sign">split-fat sign</a>: the thin peripheral rim of fat best seen on planes along the long axis of the lesion in non-fat-suppressed sequences</li>
- +<li>
- +<a href="/articles/target-sign-disambiguation">target sign</a><ul>
- +<li>peripheral high T2 signal</li>
- +<li>central low signal</li>
- +<li>rarely seen intracranially <sup>7</sup>
- +</li>
- +</ul>
- +</li>
- +<li>
- +<a href="/articles/fascicular-sign">fascicular sign</a>: multiple small ring-like structures</li>
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Case 23: schwannoma - hand
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