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Videonystagmography (VNG) – examination of the labyrinth

What does the procedure look like and what diagnosis can be made?

 

After a medical interview, the patient is seated on the ENT chair. Using an atomizer, the doctor administers anesthesia (lidocaine) to the nasal cavities, similar as when using a nasal spray. The purpose of the anesthesia is not to relieve pain as much as to eliminate gag reflex, which is common when any foreign object (in this case – a fiberscope) reaches the throat.

During the examination, the doctor uses one hand to manage the fibrescope, occasionally enabling the NBI filter to inspect the mucous membrane of the nasal cavities. Throughout the procedure, everything is explained to the patient, and the patient can take a look inside their nasal cavities, if they wish to do so.

Our patients can get the full scope of diagnostic tests: microbiological (bacteriological and mycological), allergological, histopathological, as well as for tumour markers.

 

What is videonystagmography (VNG)? 

 

Videonystagmography (VNG) in MML is a modern, essential method of diagnosing disorders of the labyrinth. Developed in 1989 in France, videonystagmography is one of few tests that enable separate evaluation of both labyrinths. During the test, the patient is asked to put on special glasses, resembling goggles used for skiing, that tightly cover the eyes and block infrared radiation.

 

A ray of infrared light is then sent to the eye, reflecting from it depending on the position of the eyeball, reaching the sensors in the glasses. The camera is connected to a computer, which gathers the data and presents it in the form of graphs for the doctor to analyze.

 

Thanks to its specific technique and the ability to comprehensively assess the vestibular system, videonystagmography is a fundamental test for diagnosing balance disorders and vertigo. The labirynth registers vertical and horizontal head movements and sends the information to the corresponding areas of the brain, which then passes it on to the muscles in the eyeballs, allowing automatic control of these muscles. When artificially stimulating a healthy labirynth, warm or cold water is administered to the ear canal, causing nystagmys (involuntary eye movements). When a labyrinth is damaged, this action is restricted. Furthermore, irritating the labyrinths can trigger symptoms such as dizziness, nausea, and sometimes even vomiting.

 

The process 

VNG test usually starts from observing spontaneous nystagmus, so it checks if nystagmus appears with no stimulants. Next are usually positional tests, examining the occurrence of nystagmus depending on the position of the body and the head of the patient. The most important trial during a VNG test is the caloric test, when air or water of varying temperature is administered to the outer ear canal using a calorizer. It causes a patient to experience nystagmus and dizziness.

 

The VNG test consists of various tests, essential to a full diagnosis of labyrinth disorders. These are:

  • spontaneous nystagmus tests
  • gaze nystagmus tests
  • saccade movements tests
  • shutter and linear tracking tests
  • optokinetic response (OKR) test
  • tests of quick change of body and head position
  • caloric reflex tests
  • rotary tests

 

What is the labyrinth? 

 

The inner ear, responsible for the senses of hearing and balance, because it reacts to changes in position of the body. It can be described as the organ of balance and spatial orientation. It is located in the petrous part of the temporal bone.

 

We distinguish the membranous labyrinth and surrounding it bony labyrinth. The membranous labyrinth consists of structures responsible not only for maintaining balance, but also for processing auditory stimuli. In a healthy organism, when resting, the impulses from the left and right labyrinths are balanced. During a movement, imbalance arises in the vestibule. When the imbalance is caused by a real trigger, the reflex is correct. However, in case of a one-sided, partial, or full labyrinth damage, an imbalance appears in the vestibular, causing a sensation of false movement – what we call dizziness.

 

Symptoms of labyrinth disorders

the primary symptoms of labyrinth disorders are:

  • dizziness, vertigo
  • trouble keeping balance
  • hearing loss
  • nystagmus
  • nausea and vomiting
  • tinnitus

 

Labyrinth disorders

 

Disorders of the labyrinth must not be ignored, because untreated, they can lead to serious complications, such as: hearing loss, deafness, and balance disorders.

 

One of the most known labyrinth disorders is Meniere’s disease. It is caused by accumulation and rising pressure of endolymph, leading to development of idiomatic hydrocele.

 

Probably the lightest type of labyrinth disease is motion sickness, especially common in children. It is caused by conflicting signals being sent to the brain by the labyrinth and eyes.

 

A much more serious and dangerous disease is tumour of the sternocerebellar angle – a type of cancer of the cochlear atrium nerve. In the early stages of this disease, the symptoms are similar to most labyrinth disorders, therefore it is crucial to take action as soon as the symptoms appear.

 

Another known labyrinth disease is otosclerosis. It attacks the bony labyrinth, causing hearing loss. Transformation of the structure of the bony labyrinth restricts movement of the stapes, leading to progressive conductive hearing loss. There are often genetic predispositions for this disease.

 

Problems with the labyrinth related to the inflammation of the middle ear are often caused by bacteria, while inflammation of the vestibulocochlear nerve is caused by viruses such as herpes, mumps, influenza, measles, chickenpox and zoster.

 

Labyrinth disorders may also appear along other diseases such as:

  • stroke
  • brain tumours
  • Addison-Biermer’s disease
  • low blood pressure
  • alcohol and drug poisoning

 

Treating the labyrinth

It is difficult to define whether the damaged labyrinth is treatable, as it depends on the type and severity of the damage. Treatment of labyrinth disorders often has to be carried  out in a hospital, where antibiotics can be administered intravenously. Sometimes it is also necessary to perform an ear drainage and in some cases, a surgical intervention.

 

How to prepare for a VNG test?

The test is recommended to patients of 7 years old or older, as it needs cooperation and conscious participation from the patient.

  • it is necessary to refrain from drinking coffee and alcohol for 24 to 48 hours before the procedure, and not eat any meals for about 4 hours before the test.
  • the ear canals must be thoroughly cleaned of ear wax
  • all makeup must be removed, especially eye makeup
  • patients wearing glasses or hearing aids on a daily basis should have it with them during the procedure
  • for the results to be as accurate as possible, the doctor may suggest to withdraw some pharmaceuticals, especially sedatives and some vertigo medication.
  • the procedure usually takes 1 to 1,5 hour. Afterwards, the patient should not be driving and sometimes, especially with elderly and more sensitive patients, it is recommended that they ask for someone to assist them, as there is a possibility of unpleasant symptoms arising.

 

Contraindications for videonystagmography

Videonystagmography is a non-invasive and safe procedure, therefore there aren’t many contraindications to performing it. If there are, they are usually linked with its technical aspects.

For example, VNG is difficult to perform for people who blink very often, therefore it can exclude patients with allergic conjunctivitis.

Some elements of the test where observation is necessary, can’t be done on blind patients. The calorimetric test should not be performed in case of a damaged tympanum, as it may worsen the damage.

Pouring water into the ear canals is not recommended when inflammation of the middle or outer ear occurs. With these diseases, it is safer to use air applicators of varied temperature.

 

Is the VNG test painful?

The VNG test is painless. However, in some parts of the test the patient may experience dizziness, nausea and discomfort. The procedure can be stopped at any moment, and the patient should communicate with the doctor and inform them of their state.

 

Price of a VNG test in Warsaw

VNG tests are not funded by the National Health Fund, but they are offered by many clinics in Warsaw. The price for a VNG test usually ranges from 100 to 250 złoty.