Vestibular schwannoma

Changed by Antonio Rodrigues de Aguiar Neto, 18 Jul 2019
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Acoustic neuromas, also known as vestibular schwannomas, are relatively common tumours that arise from the vestibulocochlear nerve (CN VIII) and represent ~80% of cerebellopontine angle masses. Bilateral acoustic schwannomas are strongly suggestive of neurofibromatosis type 2 (NF2).

On imaging, they classically present as a solid nodular mass with an intracanalicular component that often results in widening of the porus acusticus. They usually show intense contrast enhancement and, when larger, cystic degeneration can be present. Haemorrhagic areas may also be seen, but calcification is typically not present.

Epidemiology

Acoustic neuromas account for 7-8% of all primary intracranial tumours 2 and 75-90% of cerebellopontine angle masses 1,2,8. The vast majority (95%) of solitary lesions are sporadic. Bilateral vestibular schwannomas are highly suggestive of neurofibromatosis type 2 (NF2), although bilateral tumours are encountered in the familial form of acoustic schwannomas in the absence of other stigmata of NF2 5.

Vestibular schwannomas (VSs) usually occur between the fourth to sixth decades of life, with a median age of 50 years 11. VSs developing in individuals with NF II tend to be present earlier, with a peak incidence around the third decade of life.

Although rare, acoustic neuromas can occur in children.

Clinical presentation

The typical presentation is with adult-onset sensorineural hearing loss or non-pulsatile tinnitus. In some patients, this goes unnoticed, and presentation is delayed until the lesion is much larger and presents with symptoms related to mass effect. Possibilities include cerebellar and brainstem symptoms (e.g. cranial nerve dysfunction other than vestibulocochlear), or hydrocephalus due to the effacement of the fourth ventricle. 

Pathology

Acoustic neuromas are benign tumours (WHO grade 1), which usually arise from the intracanalicular segment of the vestibular portion of the vestibulocochlear nerve (CN VIII) 2,4, near the transition point between glial and Schwann cells (Obersteiner-Redlich zone) 8. In over 90% of cases, these tumours arise from the inferior division of the vestibular nerve 8.

They are well-circumscribed encapsulated masses which, unlike neuromas, arise from but are separate from nerve fibres 7, which they usually splay and displace rather than engulf.

They can display two types of growth pattern:

  • Antoni A
    • elongated cells with cytoplasmic processes arranged in fascicles 7
    • little stromal matrix
    • Verocay bodies: nuclear-free zones of processes lying between regions of nuclear palisading
  • Antoni B
    • loose meshwork of cells
    • less densely cellular
    • microcysts and myxoid change

Immunohistochemical staining is usually positive for S-100 protein 11.

Etiology
  • neurofibromatosis type 2 (defect on Chromosome 22) – bilateral acoustic neuromas
  • Exposure to high-dose radiation 

Radiographic features

Location
  • most have an intracanalicular component, often widening the porus acusticus (trumpeted IAM sign) (up to 90%) 5
    • a small "CSF cap" typically remains separating intracanalicular tumour from the cochlea; however, grow laterally through the cochlea (transmodiolar) or vestibule (transmacular) into the middle ear may occasionally occur
    • involvement of the IAC fundus is associated with decreased rates of hearing preservation
    • extracanalicular extension may result in an "ice cream cone" appearance, presumably representing tumour growth inwards along a path of least resistance
  • a minority are purely extracanalicular, merely abutting the porus acusticus (~20%) 1,5
  • rarely, small tumours may be confined to the labyrinth (see intralabyrinthine schwannoma) 4
Tumour consistency
  • small tumours tend to be solid, but larger tumour commonly demonstrate cystic degeneration 2
  • may have haemorrhagic areas
  • typically without calcification
CT

May show erosion and widening of the internal acoustic canal. The density of these tumours on non-contrast imaging is variable, and often they are hard to see, especially on account of beam hardening and streak artefact from the adjacent petrous temporal bone.

Contrast enhancement is present but can be underwhelming, especially in larger lesions with cystic components. Many cysts are loculations of CSF adjacent to a vestibular schwannoma, others represent cystic degeneration within schwannomas.

MRI
  • T1
    • slightly hypointense to the adjacent brain (63%) 2
    • isointense to the adjacent brain (37%) 2
    • may contain hypointense cystic areas
  • T2
    • heterogeneously hyperintense to adjacent brain 5
    • fluid intensity cystic areas
    • may have associated peritumoral arachnoid cysts 3
  • T1 C+ (Gd)
    • contrast enhancement is intense
    • however, heterogeneous in larger tumours
Post-operational MRI

Linear enhancement may not indicate a tumour, but if there is a nodular enhancement, suspect tumour recurrence (requires follow-up MRI).

Radiology report

The report shall describe the components intracanalicular, extrameatal, or intrameatal and extrameatal, and cross-sectional measurements should be specific for each component 11.

Treatment and prognosis

There is variability in the rate of growth of these tumours, and as such, the decision to treat requires consideration of the patient's age and co-morbidities. The options include 6 :

  • observation and follow-up
  • stereotactic radiosurgery
  • microsurgery: number of approaches are possible, including 8:
    • retrosigmoid (transmeatal) (suboccipital)
      • able to preserve hearing
      • can be used for large tumours
      • limited view of the internal auditory canal
      • has a greater chance of residual tumour (in the lateral aspect of internal auditory canal)
    • middle cranial fossa
      • best for small intracanalicular tumours
      • able to preserve hearing
    • translabyrinthine
      • careful skeletonisation of the facial nerve required (i.e. intraoperative facial nerve monitoring by needle electromyography with continuous stimulation)
      • loss of hearing guaranteed

Overall tumour recurrence is low, ranging between 1 and 9% 8.

History and etymology

The tumor was first described in 1777 by Eduard Sandifort, an anatomist from the Netherlands 12.

The first case in which a patient survived surgical resection of a vestibular schwannoma was in 1894, which procedure was performed by Sir Charles Balance, a British surgeon 12.

Differential diagnosis

The most frequent differentials to be considered are:

  • meningioma
    • usually more homogeneous in appearance: significant signal heterogeneity with cystic or haemorrhagic areas is more typical of vestibular schwannoma than meningiomas (although cystic meningiomas do occur)
    • meningiomas tend to have a broad dural base
    • usually lack the trumpeted internal acoustic meatus sign
    • large meningiomas often located asymmetrically relative to the IAC
    • calcification more common
  • epidermoid
    • no enhancing component
    • very high signal on DWI
    • does not widen the internal auditory canal
  • metastasis
    • uncommon
    • usually does not remodel the internal auditory canal, as metastases are usually present for only a short time
  • ependymoma
    • centred on the fourth ventricle
    • does not extend into the internal auditory canal
    • usually younger patients

Practical points

What the surgeon wants to know

In addition to general remarks about the size and location of the tumour, significant findings that influence surgical management include 8:

See also

  • -<p><strong>Acoustic neuromas</strong>, also known as <strong>vestibular schwannomas</strong>, are relatively common tumours that arise from the <a href="/articles/vestibulocochlear-nerve">vestibulocochlear nerve (CN VIII)</a> and represent ~80% of <a href="/articles/cerebellopontine-angle-mass">cerebellopontine angle masses</a>. Bilateral acoustic schwannomas are strongly suggestive of <a href="/articles/neurofibromatosis-type-2-3">neurofibromatosis type 2 (NF2)</a>.</p><p>On imaging, they classically present as a solid nodular mass with an intracanalicular component that often results in widening of the <a href="/articles/porus-acusticus-internus">porus acusticus</a>. They usually show intense contrast enhancement and, when larger, cystic degeneration can be present. Haemorrhagic areas may also be seen, but calcification is typically not present.</p><h4>Epidemiology</h4><p>Acoustic neuromas account for 7-8% of all primary intracranial tumours <sup>2</sup> and 75-90% of cerebellopontine angle masses <sup>1,2,8</sup>. The vast majority (95%) of solitary lesions are sporadic. Bilateral vestibular schwannomas are highly suggestive of <a href="/articles/neurofibromatosis-type-2-3">neurofibromatosis type 2 (NF2)</a>, although bilateral tumours are encountered in the familial form of acoustic schwannomas in the absence of other stigmata of NF2 <sup>5</sup>.</p><h4>Clinical presentation</h4><p>The typical presentation is with adult-onset <a href="/articles/sensorineural-hearing-loss-snhl">sensorineural hearing loss</a> or non-pulsatile <a href="/articles/tinnitus">tinnitus</a>. In some patients, this goes unnoticed, and presentation is delayed until the lesion is much larger and presents with symptoms related to mass effect. Possibilities include cerebellar and brainstem symptoms (e.g. cranial nerve dysfunction other than vestibulocochlear), or <a href="/articles/hydrocephalus">hydrocephalus</a> due to the effacement of the fourth ventricle. </p><h4>Pathology</h4><p>Acoustic neuromas are benign tumours (WHO grade 1), which usually arise from the intracanalicular segment of the vestibular portion of the <a href="/articles/vestibulocochlear-nerve">vestibulocochlear nerve (CN VIII)</a> <sup>2,4</sup>, near the transition point between glial and Schwann cells (<a href="/articles/obersteiner-redlich-zone">Obersteiner-Redlich zone</a>) <sup>8</sup>. In over 90% of cases, these tumours arise from the inferior division of the vestibular nerve <sup>8</sup>.</p><p>They are well-circumscribed encapsulated masses which, unlike neuromas, arise from but are separate from nerve fibres <sup>7</sup>, which they usually splay and displace rather than engulf.</p><p>They can display two types of growth pattern:</p><ul>
  • +<p><strong>Acoustic neuromas</strong>, also known as <strong>vestibular schwannomas</strong>, are relatively common tumours that arise from the <a href="/articles/vestibulocochlear-nerve">vestibulocochlear nerve (CN VIII)</a> and represent ~80% of <a href="/articles/cerebellopontine-angle-mass">cerebellopontine angle masses</a>. Bilateral acoustic schwannomas are strongly suggestive of <a href="/articles/neurofibromatosis-type-2-3">neurofibromatosis type 2 (NF2)</a>.</p><p>On imaging, they classically present as a solid nodular mass with an intracanalicular component that often results in widening of the <a href="/articles/porus-acusticus-internus">porus acusticus</a>. They usually show intense contrast enhancement and, when larger, cystic degeneration can be present. Haemorrhagic areas may also be seen, but calcification is typically not present.</p><h4>Epidemiology</h4><p>Acoustic neuromas account for 7-8% of all primary intracranial tumours <sup>2</sup> and 75-90% of cerebellopontine angle masses <sup>1,2,8</sup>. The vast majority (95%) of solitary lesions are sporadic. Bilateral vestibular schwannomas are highly suggestive of <a href="/articles/neurofibromatosis-type-2-3">neurofibromatosis type 2 (NF2)</a>, although bilateral tumours are encountered in the familial form of acoustic schwannomas in the absence of other stigmata of NF2 <sup>5</sup>.</p><p>Vestibular schwannomas (VSs) usually occur between the fourth to sixth decades of life, with a median age of 50 years <sup>11</sup>. VSs developing in individuals with NF II tend to be present earlier, with a peak incidence around the third decade of life.</p><p>Although rare, acoustic neuromas can occur in children.</p><h4>Clinical presentation</h4><p>The typical presentation is with adult-onset <a href="/articles/sensorineural-hearing-loss-snhl">sensorineural hearing loss</a> or non-pulsatile <a href="/articles/tinnitus">tinnitus</a>. In some patients, this goes unnoticed, and presentation is delayed until the lesion is much larger and presents with symptoms related to mass effect. Possibilities include cerebellar and brainstem symptoms (e.g. cranial nerve dysfunction other than vestibulocochlear), or <a href="/articles/hydrocephalus">hydrocephalus</a> due to the effacement of the fourth ventricle. </p><h4>Pathology</h4><p>Acoustic neuromas are benign tumours (WHO grade 1), which usually arise from the intracanalicular segment of the vestibular portion of the <a href="/articles/vestibulocochlear-nerve">vestibulocochlear nerve (CN VIII)</a> <sup>2,4</sup>, near the transition point between glial and Schwann cells (<a href="/articles/obersteiner-redlich-zone">Obersteiner-Redlich zone</a>) <sup>8</sup>. In over 90% of cases, these tumours arise from the inferior division of the vestibular nerve <sup>8</sup>.</p><p>They are well-circumscribed encapsulated masses which, unlike neuromas, arise from but are separate from nerve fibres <sup>7</sup>, which they usually splay and displace rather than engulf.</p><p>They can display two types of growth pattern:</p><ul>
  • +</ul><p>Immunohistochemical staining is usually positive for S-100 protein <sup>11</sup>.</p><h5>Etiology</h5><ul>
  • +<li>neurofibromatosis type 2 (defect on Chromosome 22) – bilateral acoustic neuromas</li>
  • +<li>Exposure to high-dose radiation </li>
  • +<li>involvement of the IAC fundus is associated with decreased rates of hearing preservation</li>
  • -</ul><h5>CT</h5><p>May show erosion and widening of the <a href="/articles/internal-acoustic-canal">internal acoustic canal</a>. The density of these tumours on non-contrast imaging is variable, and often they are hard to see, especially on account of beam hardening and streak artefact from the adjacent petrous temporal bone.</p><p>Contrast enhancement is present but can be underwhelming, especially in larger lesions with cystic components.</p><h5>MRI</h5><ul>
  • +</ul><h5>CT</h5><p>May show erosion and widening of the <a href="/articles/internal-acoustic-canal">internal acoustic canal</a>. The density of these tumours on non-contrast imaging is variable, and often they are hard to see, especially on account of beam hardening and streak artefact from the adjacent petrous temporal bone.</p><p>Contrast enhancement is present but can be underwhelming, especially in larger lesions with cystic components. Many cysts are loculations of CSF adjacent to a vestibular schwannoma, others represent cystic degeneration within schwannomas.</p><h5>MRI</h5><ul>
  • -</ul><h6>Post-operational MRI</h6><p>Linear enhancement may not indicate a tumour, but if there is a nodular enhancement, suspect tumour recurrence (requires follow-up MRI).</p><h4>Treatment and prognosis</h4><p>There is variability in the rate of growth of these tumours, and as such, the decision to treat requires consideration of the patient's age and co-morbidities. The options include <sup>6 </sup>:</p><ul>
  • +</ul><h6>Post-operational MRI</h6><p>Linear enhancement may not indicate a tumour, but if there is a nodular enhancement, suspect tumour recurrence (requires follow-up MRI).</p><h4>Radiology report</h4><p>The report shall describe the components intracanalicular, extrameatal, or intrameatal and extrameatal, and cross-sectional measurements should be specific for each component <sup>11</sup>.</p><h4>Treatment and prognosis</h4><p>There is variability in the rate of growth of these tumours, and as such, the decision to treat requires consideration of the patient's age and co-morbidities. The options include <sup>6 </sup>:</p><ul>
  • -</ul><p>Overall tumour recurrence is low, ranging between 1 and 9% <sup>8</sup>.</p><h4>Differential diagnosis</h4><p>The most frequent differentials to be considered are:</p><ul>
  • +</ul><p>Overall tumour recurrence is low, ranging between 1 and 9% <sup>8</sup>.</p><h4>History and etymology</h4><p>The tumor was first described in 1777 by Eduard Sandifort, an anatomist from the Netherlands <sup>12</sup>.</p><p>The first case in which a patient survived surgical resection of a vestibular schwannoma was in 1894, which procedure was performed by Sir Charles Balance, a British surgeon <sup>12</sup>.</p><h4>Differential diagnosis</h4><p>The most frequent differentials to be considered are:</p><ul>
  • +<li>large meningiomas often located asymmetrically relative to the IAC</li>

References changed:

  • 11. Lin E & Crane B. The Management and Imaging of Vestibular Schwannomas. AJNR Am J Neuroradiol. 2017;38(11):2034-43. <a href="https://doi.org/10.3174/ajnr.A5213">doi:10.3174/ajnr.A5213</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/28546250">Pubmed</a>
  • 11. Lin E & Crane B. The Management and Imaging of Vestibular Schwannomas. AJNR Am J Neuroradiol. 2017;38(11):2034-43. <a href="https://doi.org/10.3174/ajnr.A5213">doi:10.3174/ajnr.A5213</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/28546250">Pubmed</a>
  • 12. Silk P, Lane J, Driscoll C. Surgical Approaches to Vestibular Schwannomas: What the Radiologist Needs to Know. Radiographics. 2009;29(7):1955-70. <a href="https://doi.org/10.1148/rg.297095713">doi:10.1148/rg.297095713</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/19926756">Pubmed</a>
  • 12. Silk P, Lane J, Driscoll C. Surgical Approaches to Vestibular Schwannomas: What the Radiologist Needs to Know. Radiographics. 2009;29(7):1955-70. <a href="https://doi.org/10.1148/rg.297095713">doi:10.1148/rg.297095713</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/19926756">Pubmed</a>
  • E.P. Lin, B.T. Crane. The Management and Imaging of Vestibular Schwannomas. (2017) American Journal of Neuroradiology. 38 (11): 2034. <a href="https://doi.org/10.3174/ajnr.A5213">doi:10.3174/ajnr.A5213</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/28546250">Pubmed</a> <span class="ref_v4"></span>
  • Portia S. Silk, John I. Lane, Colin L. Driscoll. Surgical Approaches to Vestibular Schwannomas: What the Radiologist Needs to Know1. (2009) RadioGraphics. 29 (7): 1955-70. <a href="https://doi.org/10.1148/rg.297095713">doi:10.1148/rg.297095713</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/19926756">Pubmed</a> <span class="ref_v4"></span>
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