Acoustic neuroma MRI: Difference between revisions

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'''
__NOTOC__
{{Acoustic neuroma}}
{{CMG}}{{AE}}{{Simrat}}
==Overview==
[[Gadolinium]]-enhanced [[Magnetic resonance imaging|MRI scan]] is the definitive [[diagnostic test]] for acoustic neuroma and can identify [[tumors]] as small as 1-2 millimeter in [[diameter]]. On [[brain]] [[Magnetic resonance imaging|MRI]], acoustic neuroma characterized by hypointense mass on T1-weighted [[Magnetic resonance imaging|MRI]], and hyperintense mass on T2-weighted [[Magnetic resonance imaging|MRI]].
==MRI==
*[[Gadolinium]]-enhanced [[magnetic resonance imaging|magnetic resonance imaging (MRI)]] is the preferred [[diagnostic test]] for identifying acoustic neuromas and can identify [[tumors]] as small as 1-2 millimeter in [[diameter]].<ref>{{Cite journal
| author = [[E. P. Lin]] & [[B. T. Crane]]
| title = The Management and Imaging of Vestibular Schwannomas
| journal = [[AJNR. American journal of neuroradiology]]
| volume = 38
| issue = 11
| pages = 2034–2043
| year = 2017
| month = November
| doi = 10.3174/ajnr.A5213
| pmid = 28546250
}}</ref><ref>{{Cite journal
| author = [[D. F. Wilson]], [[R. S. Hodgson]], [[M. F. Gustafson]], [[S. Hogue]] & [[L. Mills]]
| title = The sensitivity of auditory brainstem response testing in small acoustic neuromas
| journal = [[The Laryngoscope]]
| volume = 102
| issue = 9
| pages = 961–964
| year = 1992
| month = September
| doi = 10.1288/00005537-199209000-00001
| pmid = 1518359
}}</ref>


{| align="center" border="0" cellpadding="1" cellspacing="1"
{| style="border: 0px; font-size: 90%; margin: 3px; width: 600px" align="center"
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|+
! style="background: #4479BA; width: 200px;" | {{fontcolor|#FFF|MRI component}}
! style="background: #4479BA; width: 400px;" | {{fontcolor|#FFF|Features}}
|-
| style="padding: 5px 5px; background: #DCDCDC; font-weight: bold" |
:T1
| style="padding: 5px 5px; background: #F5F5F5;" |
*Slightly hypointense to the adjacent [[brain]] (63%)
*Isointense to the adjacent [[brain]] (37%)
*May contain hypointense [[Cyst|cystic]] areas
|-
| style="padding: 5px 5px; background: #DCDCDC;font-weight: bold" |
:T2
| style="padding: 5px 5px; background: #F5F5F5;" |
*[[Heterogeneous|Heterogeneously]] hyperintense to the adjacent [[brain]]
*[[Cyst|Cystic]] areas [[fluid]] intensity
*May have associated [[Tumor|peritumoral]] [[Arachnoid mater|arachnoid]] [[Cyst|cysts]]
|-
| style="padding: 5px 5px; background: #DCDCDC;font-weight: bold" |
:T1 C+ (Gd)
| style="padding: 5px 5px; background: #F5F5F5;" |
*[[Contrast medium|Contrast]] enhancement is vivid
*But [[heterogeneous]] in larger [[Tumor|tumors]]
|-
|-
| Acoustic neuromas are most frequently diagnosed by MRI scan in a patient with unilateral hearing loss. Important information to be determined from the MRI scan are distance the tumor extends laterally in the auditory canal, the extent to which the tumor expands in the cerebello-pontine angle, and whether or not the brain stem is contacted or distorted
|}
|}


'''
Post-op [[Magnetic resonance imaging|MRI]]: Linear enhancement may not indicate [[tumor]]. But if there is [[Nodule (medicine)|nodular]] enhancement, suspect [[tumor]] recurrence which will necessitate follow-up [[Magnetic resonance imaging|MRI]]).<ref name="radio">Acoustic Schwannoma. Radiopedia(2015) http://radiopaedia.org/articles/acoustic-schwannoma Accessed on October 2 2015</ref>
 
* <div>The definitive diagnostic test for patients with acoustic tumors is '''gadolinium-enhanced MRI.'''
 
** Well-performed scanning can demonstrate tumors as small as 1-2 mm in diameter. On the other hand, thin-cut CT scanning can miss tumors as large as 1.5 cm even when intravenous contrast enhancement is used.
** Gadolinium contrast is critical because nonenhanced MRI can miss small tumors.
** Fast-spin echo techniques do not require gadolinium enhancement and can be performed very rapidly and relatively inexpensively. However, such highly targeted techniques risk missing other important causes of unilateral sensory hearing loss, including intra-axial tumors, demyelinating disease, and infarcts.
** MRI is contraindicated in individuals with ferromagnetic implants.
</div>
* Fine-cut CT scanning of the internal auditory canal with contrast can rule out a medium-size or large tumor but cannot be relied upon to detect a tumor smaller than 1-1.5 cm.
* If suspicion is high and MRI is contraindicated, '''air-contrast cisternography''' has high sensitivity and can detect relatively small intracanalicular tumors.
 
'''
 
{| align="center" border="0" cellpadding="1" cellspacing="1"
|-
|
 
<font>'''<font>Entirely intracanalicular</font>'''</font>
 
Since these tumors are entirely within the bony canal, they pose no threat to the brain or cranial nerves other than VII and VIII, which are in the canal. Therefore, the crucial questions are how severely affected are the nerves already and how fast is the tumor growing. Since the nerve most susceptible to pressure is the auditory component of nerve VIII, a detailed hearing test and auditory evoked potentials should be performed. If useful hearing is present, it is advisable to remove the tumor or treat it with stereotactic radiation before it becomes larger. With microsurgery, the tumor can be completely removed with minimal risk and a reasonable chance of preserving hearing. Facial nerve and auditory monitoring are, of course, required. With stereotactic radiation therapy, no actual surgery is required but the tumor will still be present and will need to be followed indefinitely by MRI scans. The outcome for preservation of hearing is similar in both techniques.


If useful hearing is not present, it is reasonable to follow the tumor for one year with a repeat MRI scan to see if it is growing before making a decision regarding surgery, radiation, or more waiting. However, if knowing you have a tumor in your head and not doing something is unacceptable, it is appropriate to proceed with surgery or stereotactic radiation.
[[File:Intracanalicular_acoustic_schwannoma.jpg|thumb|none|200px|[[Magnetic resonance imaging|MRI]] showing Intracanalicular acoustic neuroma<ref>Image courtesy of Dr Frank Gaillard. [http://www.radiopaedia.org Radiopaedia] (original file [http://radiopaedia.org/cases/intracanalicular-acoustic-schwannoma here]).[http://radiopaedia.org/licence Creative Commons BY-SA-NC</ref>]]
[[File:Intrameatal vestibularis schwannoma.jpg|thumb|none|200px|[[Magnetic resonance imaging|MRI]] showing [[Internal auditory meatus|Intrameatal]] vestibular schwannoma<ref>Image courtesy of  Dr. Roberto Schubert [http://www.radiopaedia.org Radiopaedia] (original file [http://radiopaedia.org/cases/intrameatal-vestibularis-schwannoma here]).[http://radiopaedia.org/licence Creative Commons BY-SA-NC</ref>]]


<font>'''<font>Intracranial extension without brainstem distortion</font>'''</font>
==References==
 
{{reflist|2}}
These tumors have already demonstrated their propensity to grow, but are not yet life-threatening. They should be surgically removed if the general health of the patient permits; otherwise, they should be treated with stereotactic radiation. The surgical approach depends on the status of the hearing and the preference of the surgeon, but the primary objective other than total removal of the tumor should be to preserve the facial nerve. This requires facial nerve monitoring during the course of the operation. If useful hearing is still present, an effort should be made to preserve it by intraoperative auditory monitoring and selecting a surgical approach which does not damage the cochlea.
 
<font>'''<font>Intracranial extension with brainstem distortion</font>'''</font>
 
Large tumors which distort the brain stem are potentially life-threatening and should be surgically removed as soon as possible. The goal should be total removal, but great care must be taken to ensure that neither the brain stem nor its blood supply are injured in the process. Preservation of the facial nerve also remains important, and it may be necessary to leave a portion of tumor capsule to protect the brain stem, blood vessels or facial nerve. The possibility of preserving any hearing with large tumors is minimal
|}


'''
{{WH}}
{{WS}}
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Latest revision as of 18:00, 26 April 2019

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2]

Overview

Gadolinium-enhanced MRI scan is the definitive diagnostic test for acoustic neuroma and can identify tumors as small as 1-2 millimeter in diameter. On brain MRI, acoustic neuroma characterized by hypointense mass on T1-weighted MRI, and hyperintense mass on T2-weighted MRI.

MRI
MRI component Features
T1
  • Slightly hypointense to the adjacent brain (63%)
  • Isointense to the adjacent brain (37%)
  • May contain hypointense cystic areas
T2
T1 C+ (Gd)

Post-op MRI: Linear enhancement may not indicate tumor. But if there is nodular enhancement, suspect tumor recurrence which will necessitate follow-up MRI).[3]

MRI showing Intracanalicular acoustic neuroma[4]
MRI showing Intrameatal vestibular schwannoma[5]

References

  1. ↑ E. P. Lin & B. T. Crane (2017). "The Management and Imaging of Vestibular Schwannomas". AJNR. American journal of neuroradiology. 38 (11): 2034–2043. doi:10.3174/ajnr.A5213. PMID 28546250. Unknown parameter |month= ignored (help)
  2. ↑ D. F. Wilson, R. S. Hodgson, M. F. Gustafson, S. Hogue & L. Mills (1992). "The sensitivity of auditory brainstem response testing in small acoustic neuromas". The Laryngoscope. 102 (9): 961–964. doi:10.1288/00005537-199209000-00001. PMID 1518359. Unknown parameter |month= ignored (help)
  3. ↑ Acoustic Schwannoma. Radiopedia(2015) http://radiopaedia.org/articles/acoustic-schwannoma Accessed on October 2 2015
  4. ↑ Image courtesy of Dr Frank Gaillard. Radiopaedia (original file here).[http://radiopaedia.org/licence Creative Commons BY-SA-NC
  5. ↑ Image courtesy of Dr. Roberto Schubert Radiopaedia (original file here).[http://radiopaedia.org/licence Creative Commons BY-SA-NC

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