Protocol
Based on the clinical evaluation, the optimal imaging modality is selected.
If there is a clinical suspicion for a central cause of the vertigo, such as a stroke or CPA tumor, an MRI of the tem- poral bone is the initial study of choice.
If there is high clinical suspicion of otospongiosis, perilymphatic fistula, or SSCD, a noncontrast CT of the temporal bone should be performed.
In those cases where the cause is unclear, an MRI is usually performed as the initial study.
Interpretation Clinical Background
The differential diagnosis of dizziness and vertigo includes Meniere disease, labyrinthitis, benign paroxysmal positional vertigo (BPPV), vestibular neuritis (vN), perilymphatic fis- tual (PLF), SSCD, migraine, stroke, Chiari I malformation, and CPA tumors.
Most patients referred to the otologist have true vertigo, which is defined as a false sense of motion. Many patients with true vertigo can be further categorized based on the temporal pattern of the vertigo (persistent or episodic) and the presence or absence of hearing loss, into Meniere disease (episodic vertigo with hearing loss), labyrinthitis (persistent vertigo with hearing loss), BPPV (episodic ver- tigo, no hearing loss), and vN (persistent vertigo, no hearing loss).
As with tinnitus, most often imaging is not indicated in the work-up of vertigo. When imaging is requested, the primary goal is to determine if there is a central cause for the vertigo.
Clinical Questions
• Can we rule out a central cause of the vertigo, such as stroke, tumor, or Chiari malformation, so that the cause of the vertigo can be attributed more definitively to the inner ear?
• Is there evidence of labyrinthitis?
Fig. 1.6 The use of three-dimensional time of flight magnetic reso- nance angiography (3D TOF MRA) to detect a dural arteriovenous fis- tula. A source image from a 3D TOF MRA shows abnormal arterialized flow in the right sigmoid notch (short arrow) and transverse sinus ipsi- lateral to the patient’s symptoms of pulsatile tinnitus and multiple transmastoid perforators likely arising from the occipital branch of the right external carotid artery. On the contralateral side, no flow-related signal is seen in the dural sinus.
• Is there evidence of bony erosion to suggest a perilym- phatic fistula?
• Is there evidence of SSCD?
Approach
Because the primary goal of imaging is usually to rule out a central cause for the vertigo, a medial-to-lateral (or deep-to-superficial) approach may be used.
• Check the cerebellum, brainstem, and supratentorium for evidence of infarct (especially the vestibular nuclei in the medulla), disorder of myelination, malformation such as a Chiari I, or evidence of neurodegeneration such as spinocerebellar ataxia. In children this component of the evaluation should include a search for evidence of neurodegenerative disorders, such as Friedreich ataxia, mitochondrial disorder, or inherited disorder of myeli- nation, such as Fabry disease.36
• Evaluate the vertebrobasilar system for evidence of stenosis and atherosclerosis that may suggest verte- brobasilar insufficiency.
• Check CN VIII, the IAC, and the CPA cistern for evidence of tumor. Abnormal enhancement of CN VIII may con- firm nerve pathology, such as neuritis or leptomeningeal disease.
• Evalute the membranous labyrinth for evidence of labyrinthitis. Look for either loss of signal on the CISS, 3D FIESTA, or DRIVE sequence or abnormal enhancement.
• Evaluate for SSCD or perilymphatic fistula if CT is available.
Report
On the right/left, no vestibular lesion is seen. CN VIII appears normal; there are no findings specific for inflammation. The cerebellum and brainstem appear normal. There are no find- ings to suggest a disorder of myelination. The vertebral and basilar arteries appear normal.
Impression: No evidence of vestibular lesion
Acknowledgment The authors would like to acknowledge the contribution of Dr. Barbara Hum in the section on tinnitus.
Chapter 1 Temporal Bone Imaging Technique
23
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The external ear, comprised of the pinna or auricle and the external auditory canal (EAC), has a different embry- ological origin than that of the middle and inner ears. This unique embryonic origin, in conjunction with the superfi- cial location of the pinna and EAC, results in a distinct pathology spectrum when compared with that involving the middle and inner ears. Despite the ease of visualization of these external structures by the otolaryngologist, the radiologist can assist with important information for surgical planning and aid in determining the type and extent of the pathology. Intracranial complications arising from disorders of the pinna and EAC can also be evaluated by the radiologist.