DIFFERENTIAL DIAGNOSIS OF PERIPHERAL VESTIBULAR DISORDERS

Differential Diagnosis of Peripheral Vestibular Disorders

PART 5: Perilymphatic Fistula

Perilymphatic fistula (PLF) is the abnormal opening of the bony capsule or round/oval window membranes of the inner ear. Symptoms are variable but can include episodic vertigo, fluctuating and progressive hearing loss, tinnitus, and aural fullness. The most common causes of PLF are trauma, surgery, cholesteatoma and congenital abnormalities. The diagnosis of PLF can be very challenging even for the most experienced neuro-otologist and may still be in doubt even after surgical exploration. Initial treatment is usually bed rest with head elevation for acute PLF in hopes of spontaneous healing. For chronic PLF, surgical exploration with repair is usually indicated.

Classification

The presentation for a PLF may be varied depending on the cause of the PLF. PLF can be classified by its cause:

iatrogenic (usually post-stapedectomy)
traumatic
erosive
congenital
spontaneous.

For traumatic PLF, the trauma may be direct, implosive or explosive. Direct trauma would include blunt and penetrating injuries to the temporal bone. Implosive trauma is any trauma that would cause deflection of the round or oval windows inward and result in a subsequent membrane disruption. An example of this would be an open hand slap to the ear, water skiing accidents, barotrauma from scuba diving, and violent nose-blowing. Explosive trauma is seen when internal pressure results in outward disruption of the round or oval window membranes. This can be seen with forms of Valsalva such as physical exertion as in weight lifting, violent coughing/vomiting, blunt abdominal/thoracic trauma and childbirth. A classic presentation for this would be a weight lifter who, while straining at the bench press, notes a sudden pop in his ear followed by hearing loss and vertigo.

Those patients with congenital inner ear abnormalities or who have undergone stapes surgery are at particular risk of developing a PLF under these scenarios. Another classification of PLF is the spontaneous variety – those without any antecedent trauma or predisposing factors. The spontaneous PLF is a controversial entity and probably represents patient who had some inciting event that has been forgotten or not correlated with their vestibular symptoms.

The usual location for a PLF is the round or oval window and usually they are the result of trauma. But, erosive processes can result in PLF of the bony otic capsule. The most common clinical entity that causes an erosive PLF is cholesteatoma and the most common place for it to erode into is the horizontal semicircular canal. Other erosive processes that can cause PLF are syphilis and tumors.

A recently described variation of PLF is superior semicircular canal dehiscence. Some patients with symptoms of PLF have been noted on high resolution CT scan to have an absence of bone covering the superior aspect of the superior semicircular canal. Clinical experience with this entity is limited at this time but repair of the defect appears to be curative.

Pathophysiology

The pathophysiology of PLF is poorly understood. The leading theory to explain the symptoms is the double membrane break theory. This theory proposes that in order for hearing loss and vertigo to result from a PLF, there must be a concomitant break of an inner ear membrane. It is generally accepted that mechanisms to explain audiovestibular dysfunction attributed to PLF include direct damage to the end organ, disruption of the fluid hydrodynamics of the inner ear, and electrolyte abnormalities caused by the mixture of perilymph and endolymph. A secondary endolymphatic hydrops due to the relative excess of endolymph has been demonstrated in experimental PLF and also air in the inner ear may contribute to the possible pathophysiology of audiovestibular impairment of PLF.

Diagnosis

The patient’s history is the most important key in making the diagnosis of PLF. The hallmark of PLF is its variability of symptoms; none of which are pathognomonic. The patient may have auditory symptoms but no vestibular symptoms or vestibular symptoms but no auditory symptoms. Most commonly, however, there is usually evidence of both auditory and vestibular dysfunction. The auditory symptoms include fluctuating hearing loss, progressive hearing loss, and no hearing loss. Tinnitus may be present.

The vestibular symptoms may be described as episodic vertigo with or without nausea/vomiting, positional vertigo, intermittent dysequilibrium or chronic disequilibrium. The vertiginous spells, when present, may last as long as several hours or be as short as a few seconds. Worsening of vestibular symptoms with physical straining is an important historical finding. Tullio’s phenomenon is the finding of sound induced nystagmus/vertigo and has been noted with PLF. Probably the most helpful part of the history is whether there has been a predisposing factor (i.e. prior ear surgery, congenital inner ear abnormality) or an inciting traumatic event. There is no constellation of symptoms which is diagnostic for PLF and this may be a difficult entity to distinguish from other vestibular disorders, particularly Meniere’s disease.

Characteristic Clinical Presentation:

Inciting event – trauma, straining, erosive process (cholesteatoma, syphilis, tumor)
Chronic disequilibrium, episodic vertigo
Auditory symptoms – hearing loss, fluctuating hearing, progressive hearing loss, tinnitus
Exacerbation of dizziness with physical exertion

General physical examination is usually normal in PLF patients. Otoscopy should be carefully performed in order to evaluate the possibility of recent trauma, prior surgery, or evidence of cholesteatoma. Pneumatic otoscopy has been used to perform the office "fistula test". While varying positive and negative pressure to the ear canal with the pneumatic otoscope, the patient’s eyes are examined for nystagmus and he is asked to relay any symptoms of vertigo/disequilibrium. An abnormal test indicative of a PLF occurs when nystagmus is noted.

The subjective sensation of dizziness noted by the patient is usually a less accurate indicator of PLF. The sensitivity of the fistula test can be improved by more objective means of evaluating the physiologic response. This can be done with ENG monitoring of the eyes while the pressure is applied to the ear or postural sway can be measured on computerized dynamic platform posturography (CDPP) while pressure is applied. However, even with such objective monitoring, there is still a fair false positive and false negative rate for the fistula test.

Audiometry may demonstrate normal hearing or a unilateral hearing loss. Unfortunately, there is no characteristic hearing loss associated with PLF. ENG testing may show reduced caloric function in the affected ear, positional nystagmus, spontaneous nystagmus, or it may be completely normal. There is no completely accurate diagnostic test for PLF, but work up should include a search for other possible causes. The differential diagnosis includes Meniere’s disease and all the entities included in the Meniere’s differential. Tests generally used to exclude other etiologies are radiographic imaging (especially MRI), syphilis serology, chemistry panel, thyroid panel and an autoimmune panel.

Initial treatment of an acute traumatic PLF is strict bed rest for 4-7 days with head elevation and avoidance of straining for an additional 6 weeks. Treatment of chronic round or oval window PLF generally requires middle ear exploration with repair of the defect. PLF associated with erosive processes such as cholesteatoma and tumors requires more involved treatment of the underlying process with appropriate repair of the defect.

Return to Top

Return to Table of Contents