Chapter 16 Imaging the Dizzy Patient
Overview of imaging options
I.
In General, Who Benefits from Imaging?
a. When central etiology of dizziness or vertigo is suspected
b. Metabolic or peripheral causes of dizziness do not require imaging
c. Reserved for atypical clinical features
i. Cranial nerve palsies
ii. Facial numbness
iii. Posterior fossa tumors
iv. Vascular disease
v. Demyelination
II.
III.
IV.
What Information Should Be Provided to the Radiologist
a. For best patient care-Team approach
i. Neurotologist/neurologist
ii. Neuroradiologist- prescribes the correct imaging procedure and writes report addressing
relevant issues
iii. Otologist informs neuoradiologist of pertinent history and physical findings before
imaging
Which Imaging Modalities Are Available for the Workup of the Dizzy Patient?
a. CT- Computed Tomography
b. MR- Magnetic Resonance Imaging
c. Catheter angiograph-invasive
d. Angiography
e. PET- Positron Emission Tomography
f. SPECT- Single Photon Emission Computed Topography
g.
What Are the Advantages and Disadvantages of CT?
a. Advantages:
i. Reliably displays small anatomic parts well
ii. Modality of choice in evaluating the temporal bone
iii. Depicts cerebral tissue moderately well
iv. Calcified lesions are well seen (i.e., meningiomas)
v. Rapid scanning speed
vi.
b. Disadvantages
i. Falters when attempting to differentiate soft tissues with similar densities-gray and white
matter
ii. Plaques of Multiple Sclerosis are poorly seen
iii. Usually limited to axial and sometimes coronal display
iv. Changing the plane requires moving the patient
v. Procedure can be difficult for frail, elderly patients with arthritis in the cervical spine
vi. Beam hardening, a technical artifact, obscures the anatomy
vii. Intraveneous iodinated contrast material improves conspicuity of brain lesions but there
is a risk of anaphylaxis and renal impairment
V.
Which Patients Should Be Studied with CT?
a. Studies bony anatomy- patients with suspected lesions in the temporal bone
b. Can depict a large cochlear aqueduct, dehiscent carotid canal, dehiscent jugular fossa, ectopic
carotid artery canal, otosclerosis, fractures extending into the labyrinth, and bony dysplasias.
cholesteotoma
c. Conductive hearing loss accompanied by vertigo
VI.
What are the Advantages and Disadvantages of MR Imaging?
a. Advantages:
i. Exploits the properties of the atomic nucleus
ii. Resolve subtle differences in the water content of tissues, such as gray and white matter
iii. Portrays anatomy in slice format- multiple planes of orientation without repositioning
patient
iv. Beam hardening artifacts do not occur
v. Modality of choice for studying the posterior fossa anatomy
vi. Angiographic of large intracranial and extracranial vessels
vii. Does not require contrast material
viii. Can add screening information about the vertebrobasilar arterial system and carotid
bifurcations
ix. Venous system can be displayed
b. Disadvantages
i. Lacks spatial resolution of CT
ii. Patients with ferromagnetic or electrical medical appliances are excluded because of
potential appliance motion, dislodgement and malfunction
iii. Reported deaths from aneurysm clip motion
iv. Fails to image calcifications and cortical bone
v. More time to complete than CT
vi. Anxiety and claustrophobia prompted by machine
vii. MR angiography is inferior to catheter angiography
VII.
Which Patients Should Be Studied with MR Imaging?
a. Patients with vertigo when a central lesion is suspected- abnormal findings on vestibular testing
b. Preferred modality for evaluating retrocochlear causes of vertigo and dizziness
c. High resolution scans can image internal auditory canal, labyrinth, and vestibular aqueduct,
small intracanalicular solitary vestibular schwannomas, and labyrinthitis
d. Detects cerebral infarction,
e. MR angiography can define basilar artery stenosis
f. Hydrocephalus, mass lesions,
g. Diagnosing atherosclerotic stenosis and vascular compression of nerves
VIII.
What Are the Advantages and Disadvantages of Catheter Angiography?
a. Invasive test-femoral artery is cannulated with a catheter and iodinated contrast material is
injected into arteries of the neck and head
b. Reference standard for all modalities examining the blood vessels
IX.
Which Patients Should Be Studied with Catheter Angiography?
a. Reserved for patients with vertigo and high probability of being arterial
b. Used to determine the degree of vascularity of a lesion with previously documented pathology
SPECIFIC GUIDELINES AND A STEP-BY-STEP APPROACH
X.
What If I Suspect That My Patient Has a Retrocochlear Problem as a Solitary Vestibular
Scwannoma?
a. Solitary vestibular schwannomas present with sensorineural hearing loss in more than 70% of
patients
b. MRI should be first imaging test
XI.
What If I Suspect That My Patient Has a Vascular Problem Such as Vertebrobasilar Insufficiency?
a. Vascular causes for vertigo are common in elderly patients
b. Suspected in patients with risk factors for cerebrovascular disease, sudden recurrent episodes of
vertigo lasting days or weeks, subjective feelings of lightheadedness after neck extension, and no
accompanying hearing loss or vertigo
c. Acute symptoms
i. CT scan
ii. MR is also recommended in the acute setting
iii. Catheter angiography also used in the evaluation of acute vertebrobasilar vascular disease
d. Chronic symptoms
i. MR recommended for chronic vertebrovasilar ischemia
ii. Vascular loops
XII.
What If I Suspect That My Patient Has Some Other Central Problems Such as Multiple Sclerosis?
a. Approximately 10% of patients with MS develop vertigo- initial presenting symptom
b. MR is the preferred modality for screening for demyelination
XIII.
What if I Suspect That My Patient Has a Labyrinthine Problem Such as Labyrinthitis?
a. Chronic labyrinthitis, acute labyrinthitis, and congenital anomalies may be detected with MRI
XIV. What If I Suspect That My Patient Has Vertigo Caused by a Complication of Cholesteatoma?
a. High resolution CT imaging of the temporal bone is recommended
b. Both axial and coronal planes should be performed
XV.
What If I Suspect That My Patient Has Meniere’s Disease? Should I Ever Request Imaging
a. Meniere’s disease does not typically need confirmation with imaging
b. MR scanning is recommended for excluding labyrinthine pathology such as small vestibular
schwannoma
c. MR can identify congenital and acquired abnormalities such as enlargement of the
endolymphatic sac and cystic malformed lateral semicircular canals