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Findings: Image #1 is a T1 weighted axial image through the internal auditory canals demonstrating bilateral 8th nerve masses with extension into the porous acousticus of the internal auditory canal bilaterally.
Image #2 is a post contrast-enhanced T1 weighted axial image through the same region demonstrating diffuse homogeneous enhancement of these masses. Again, there is demonstration of the masses extending into the porous acousticus.
Diagnosis: Bilateral acoustic neuromas in a patient with neurofibromatosis Type II.
Discussion: Acoustic neuromas are benign tumors arising from cranial nerve 8. These are usually located within the internal auditory canal in the region of the cerebellar pontine angle. The vestibular nerve is the most common site of origin of this lesion. Enlargement of the acoustic neuromas in the internal auditory canal may result in progressive neuro sensory loss as well as tinnitus secondary to compression of the cochlear and vestibular nerves. In addition, patients may present with vertigo. The imaging characteristics of acoustic neuromas may be variable, but they generally present as enlargement of the 8th cranial nerve, often with extension into the porous acousticus of the internal auditory canal. The lesions most characteristically demonstrate diffuse and homogeneous enhancement on post Gadolinium enhanced scans. In general, MRI has a greater sensitivity in the detection of acoustic neuromas than does computed tomography. As the tumor enlarges, it may cause distortion of the posterior fossa as well as brain stem herniation and compression of the fourth ventricle. Rarely, acoustic neuromas may be cystic. Bilateral acoustic neuromas are a common finding in patients with neurofibromatosis Type II. In one recent study, MR images in 10 of 11 patients with neurofibromatosis Type II demonstrated bilaterally enlarged seventh and eighth nerve complexes which eventually proved to be acoustic neuromas. Other intracranial abnormalities which are associated with neurofibromatosis Type II include meningiomas as well as ependymomas and occasionally neuromas involving the other cranial nerves.
References:
Shigeki Aoki. Neurofibromatosis Types I and II: Cranial MR Findings.
Radiology. 1989;172:527-534.
Haaga JR. Computed Tomography and Magnetic Resonance Imaging of the Whole Body.
Mosby, St. Louis; 1994:451-452.
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