Dizziness

What are dizziness and vertigo? How are they different?

Nearly everyone has felt lightheaded, faint, "woozy," or unsteady at some point. In fact, nearly half of all people have at least on such an episode by the time they are 40 years of age.

Vertigo is the sensation of spinning or whirring of one's local environment in addition to unsteadiness. Dizziness is the feeling of imbalance or lightheadedness without the accompanying sensation of spinning of one's surroundings.

When episodes of dizziness or vertigo become persistent or recurrent, the individual should consult one's physician.

What causes dizziness and vertigo?

The sense of balance is maintained by various brain processes involving nerve signals coming from the ears (also known as the vestibular system), eyes, muscles, and skin. Dizziness and vertigo can occur when the function of this delicate system is disrupted. For example, an inner ear infection may produce vertigo. Problems with blood circulation, allergies, or neurological conditions may also produce symptoms.

Most causes of dizziness and vertigo are minor and easily diagnosed and treated in the doctor's office. Occasionally, a patient may require more detailed evaluation and a referral to a neuroimaging specialist—the neuroradiologist. A neuroradiologist is a physician who has extensive special training in all facets of imaging of the brain, and he or she coordinates and interprets findings from tests such as computed tomography (CT) and magnetic resonance imaging (MRI). Imaging enables the neuroradiologist to noninvasively see various parts of the brain, its coverings, and its blood vessels. Imaging provides a powerful tool that supplements other laboratory tests.

Who benefits from imaging?

Physicians sometimes classify the causes of vertigo and dizziness into peripheral and central types. Peripheral conditions include conditions that affect the inner ears, such as infection or traumatic injury. Central conditions involve the brain. Patients in whom a central cause of dizziness or vertigo is suspected may benefit from imaging, whereas patients with peripheral causes of dizziness usually do not require imaging.

What can imaging show?

Imaging can reveal the presence of narrowed blood vessels that may restrict blood flow and result in poor circulation. These findings are sometimes seen in patients with high blood pressure, diabetes, or high blood cholesterol levels. In these conditions, the brain does not receive enough blood, and vertigo or dizziness may result. Rarer conditions, such as growths or tumors that press on the brain and nerves and multiple sclerosis, are readily evaluated with imaging.

What information should the patient tell the neuroradiologist before imaging?

A team approach among the referring physician, the neuroradiologist, and the informed patient provides the best care. The patient and the referring physician should inform the neuroradiologist of the background of the symptoms and physical findings prior to imaging. Indicating the side (left or right) on which any symptom occurs is extremely important and helpful. The neuroradiologist should also be told of any previous imaging studies performed at other institutions because the previous imaging examinations may provide insight into the patient's condition and allow the physicians to better monitor changes in the patient's condition.

The neuroradiologist can then prescribe the correct imaging procedure and provide a complete report about the findings and relevant issues.

What imaging modalities can be used to evaluate dizziness?

CT and MRI have now emerged as the best methods for evaluating the balance system. These modalities display the bony and soft tissue anatomy. Catheter angiography also portrays the vascular anatomy. Although strides have been made in the use of positron emission tomography (PET) and single photon emission computed tomography (SPECT), these techniques are often unavailable in a community hospital, and they are not widely used in the evaluation of a patient with dizziness.

What are the advantages and disadvantages of CT?

CT nicely displays the bones that surround the middle and inner ear. Tiny bones and other middle ear structures are exceptionally well depicted. CT also depicts brain tissue moderately well, or as well as it shows the blood. A certain type of benign tumor, known as a meningioma, is also well depicted with CT.

The administration of an intravenous iodinated contrast material improves the detection of many brain conditions. Recently developed nonionic agents are usually well tolerated by most patients.

Another major advantage of CT in the patient with dizziness is the rapid scanning speed. An entire brain examination may require less than a minute. A new technique known as CT angiography (CTA) displays blood vessels with exceptional detail.

Who should be studied with CT?

CT is best for examining bony structures. Therefore patients with suspected conditions in the bone that surround the middle and inner ears usually benefit from CT. For example, CT can reveal bony birth defects that had been silent until the onset of dizziness or vertigo. CT also demonstrates the complications of infection and a condition known as cholesteatoma that may destroy some of the structures in the ear.

What are the advantages and disadvantages of MRI?

In MRI, a powerful magnetic field and radio waves work together to produce images. MRI may also involve the use of intravenous contrast material to more clearly show abnormalities. MRI has become the study of choice for examinations of the brain.

Patients with various metal-containing (ferromagnetic) internal devices or electrical medical appliances (eg, cerebral aneurysm clips, dorsal column stimulators, certain heart valves, cardiac pacemakers, cochlear implants, ocular metallic foreign bodies, and stapes prostheses) should consult their physician prior to undergoing an MRI. The magnetic field can potentially cause the appliance to move, to become dislodged, and/or to malfunction, and patient injury can result.

MRI also requires more time to complete than CT. Therefore, if patients cannot remain still for this time, the motion may blur the images. Elderly, restless, or critically ill patients may have difficulty tolerating prolonged periods within the MRI machine when they are required to remain motionless.

Patients who have experienced claustrophobia in the past may have a similar problem with MRI. A mild, orally administered sedative may be helpful, if the patient does not have a contraindicating medical condition or if he or she is not planning to operate a motor vehicle after the examination. These patients should contact their physician prior to the procedure. Low-field-strength machines, so called "open" MRI units, have become popular in recent years. These machines are less confining. However, the anatomical detail of the images produced by these machines may be insufficient for the diagnosis of subtle abnormalities.

MRI can also depict large intracranial and extracranial vessels. Like CTA, MR angiography (MRA) can add significant information.

Who should be examined with MRI?

MRI is very useful in patients with a suspected central cause for vertigo or dizziness. Patients with vertigo and abnormal findings on vestibular testing may also have abnormal MRI findings. Because brain tissue is better seen with MRI than with CT, MRI is now preferred for demonstration of the cerebral hemispheres, the brain stem, and the cerebellum. MRI also superbly demonstrates tumors and multiple sclerosis.

MRI also depicts findings of stroke (also known as an infarct). Newly developed diffusion-weighted MRI can be used to detect a stroke within hours of its onset. MRA can also show blood vessel narrowing, which may contribute to symptoms. Information derived from images of the blood vessels can be used in diagnosing atherosclerotic stenosis (hardening of the arteries) and compression of nerves due to tortuous blood vessels. High-resolution imagery is used to examine the brain in detail for those rare patients who present with epilepsy and dizziness or unsteadiness.

What are the advantages and disadvantages of catheter angiography?

The trained neuroradiologist may recommend catheter angiography if a more detailed study of the blood vessel is desired. Catheter angiography is a special test in which a thin tube called a catheter is placed into the major leg artery at the groin with the patient under local anesthesia. The catheter is carefully guided through the circulation into the arteries of the neck. Iodinated contrast material, which shows up on X-rays, is injected, and images are made. The risk of stroke as a result of catheter angiography is small (0.3% in modern imaging departments supervised by skilled neuroradiologists). The patient's activity is limited for several hours after the examination to prevent hematoma formation and bruising at the puncture site.

Catheter angiography can also be used as a therapeutic tool. Angioplasty, balloon occlusion, therapeutic drug infusion, arterial stent placement, and vascular obliteration can be performed for a variety of indications such as aneurysm and tumor. Occasionally, therapeutic angiography can replace surgery. Although catheter therapy is not always recommended, it may have a limited application in a patient with dizziness.

Who should be studied with catheter angiography?

Catheter angiography should be reserved for patients in whom vertigo is likely to be caused by a problem in the blood vessels that restricts blood flow or causes pressure on one of the balance centers of the brain. Such conditions include clots in major arteries, blood-vessel malformations, blood-vessel inflammation (known as vasculitis), blood-vessel dilatation (known as aneurysm), vessels that compress nerves, and arterial injury (known as dissection).

Summary

The neuroradiologist applies modern imaging of the brain to effectively supplement the clinical examination of the patient with dizziness or vertigo. CT, MRI, and catheter angiography reveal detailed anatomical information about the body's balance system. Consultation with the neuroradiologist ensures that the appropriate test is performed and that the correct diagnosis is made.

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