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Neuroradiology Case of the Week
Case 263
Brady Huang, MD and P-L Westesson, MD, PhD, DDS
Clinical
Presentation: Patient is a
49-year-old female with headaches and mild hearing loss in the left ear.
Imaging Findings:
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Figure 1: Axial FIESTA image at the level of the IAC's show a 4mm lesion in the fundus of the left internal auditory canal (IAC), just at the cochlear aperture. This lesion is isointense to the cranial nerves entering the IAC.
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Figure 2: Axial thin T1-weighted image shows that the lesion is slightly hyperintense to gray matter.
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| Figure 3. Axial fat-suppressed T1-weighted image after contrast administration shows that the lesion strongly enhances. |
Diagnosis: Intracanalicular acoustic schwannoma
Discussion: Please see Neuroradiology Case of the Week # 213 regarding the previous discussion on acoustic schwannomas, imaging characteristics, and clinical issues. In summary acoustic schwannomas are benign tumors arising from Schwann cells that encircle the vestibulocochlear nerve. They may arise within the IAC or present as a cerebellopontine angel (CPA)-IAC mass.
With the advent of 3T imaging, high-resolution images of the brain may be obtained. With respect to acoustic schwannomas, two negative prognostic findings are important to consider for hearing preservation: size greater than 2 cm and involvement of the IAC fundus and/or cochlear aperture. If hearing is already lost or greatly diminished, surgical removal will not restore hearing. Also it is important to look for a "labrythine tail" in order to differentiate acoustic schwannomas from facial nerve schwannomas as these two entities may mimic each other [1].
As shown in this case, 3T can improve MR imaging in many domains. The higher SNR at 3T allows for higher pixel matrix, thinner slices, and reducing averaging resulting in shorter scan times [2]. Slice thickness can be reduced to 3 mm and below, without substantial loss of SNR. Azmi and Schulder also showed that images obtained at 3T were accurate as stereotactic data sets, when compared to CT and 1.5T MR imaging [3].
References:
- Harnsberger, R. Diagnostic Imaging: Head and Neck. Amirsys 2004.
- Runge VM, Case RS, Sonnier HL. Advances in clinical 3-tesla neuroimaging. Invest Radiol. 2006 Feb;41(2):63-7. [Medline]
- Azmi H, Schulder M. Stereotactic accuracy of a 3-tesla magnetic resonance unit. Stereotact Funct Neurosurg. 2003;80(1-4):140-5. [Medline]
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