Perilymphatic Fistula

Etiology

Labyrinthine fistulas can be a consequence of a congenital otologic disorder, acquired by physical injury or from an iatrogenic cause. The most common causes are head injuries from trauma, labor, coughing, sneezing, pathologies that lead to increased intracranial pressure, blast injuries, diving, and flying barotrauma. Unique causes that have been reported included lightning strikes, airbag trauma, and acoustic trauma from the sirens of fire engines and other loud modalities.[2] Sneezing specifically has been seen to cause an increase in the cerebrospinal fluid pressure leading to rupture of the round window membrane resulting in such types of fistulas.

Cholesteatomas caused by chronic otitis media are another cause of perilymphatic fistulas. The reported incidence of cholesteatoma-induced perilymphatic fistula varies from 4% to 15%.[3] Cholesteatomas are known to erode bone, leading to a number of complications, including fistulas. The lateral semicircular canal is most often involved. However, the other semicircular canals can be involved as well. Furthermore, although rare, complications involving the cochlea may be involved as well.[4] Cochlear fistulas often have fistulas in other parts of the labyrinth.[4]

Epidemiology

Labyrinthine fistulas are rare, and the prevalence/incidence generally has not been well reported. The incidence of cholesteatoma-induced fistulas from chronic otitis media has been reported to be between 4% to 15%.[3]

Pathophysiology

The exact mechanism and pathophysiology are not well defined. In animal models, it was associated with air bubbles that lead to profound sensorineural hearing loss by the disruptions of the propagation of the acoustic waves traveling in the basilar membrane.[5] 

The pneumolabyrinth itself may cause severe irritation leading to severe rotational vertigo. Because the labyrinth is connected to the cochlea, fistula formation can lead to sensorineural loss and vertigo. Additionally, those fistulas that arise with cholesteatoma can cause erosion of the endochondral bone that overlies the labyrinth leading to fistulas.[6] Perilymphatic fistulas caused by physical exertion like weightlifting, coughing, or sneezing are thought to occur due to increased cerebrospinal fluid pressure that is then transferred to the labyrinth by the cochlear aqueduct or internal auditory canal.[7]

History and Physical

A careful history and physical is necessary, as a labyrinthine fistula can easily be missed or misdiagnosed. A labyrinthine fistula should be suspected in patients that sustain a temporal bone fracture or membranous labyrinthine rupture from head trauma, which includes implosive (Valsalva, blowing nose) and explosive (increased intracranial pressure from sneezing, coughing, weight lifting, and blast injuries). The primary symptoms of a traumatic labyrinthine fistula are sensorineural hearing loss and dizziness following the trauma.[7] Hearing loss is often sudden or progressive and can manifest days after a trauma. Dizziness often presents as disequilibrium, severe vertigo, or positional dizziness.[7] 

A labyrinthine fistula should also be suspected if a patient has vestibular disturbances and/or hearing loss after a stapedectomy. The artificial prosthesis can become dislodged, leading to perilymph leakage. Finally, a labyrinthine fistula should be suspected in those who have chronic otitis media. Cholesteatomas often form in these individuals, which can lead to erosion of the petrous bone that surrounds the labyrinth causing a fistula. Barotrauma is a possible cause, such as from diving or flying.[2] Perilymphatic fistula should be suspected in those that complain of dizziness and sudden or progressive sensorineural hearing loss after barotrauma.[7] 

Important exam findings include the positive fistula test, where air is insufflated in the ear, causing nystagmus. A cholesteatoma may also be seen with the otoscopic evaluation.

Another important exam finding is Tullio’s phenomenon, where dizziness occurs after introduction to sound. The patient may have a hearing loss that may be sensorineural, conductive, or a combination of the two.[5] Because of the variability of hearing loss, a tuning fork may be of limited use.

The Fukuda/Unterberger test determines postural instability from vestibular hypofunction.[2] A patient is asked to walk forward with their eyes closed and then abruptly turn with one foot and stop. The test is positive if the patient is unable to stabilize their balance after stopping. Generally, 64% of patients had a history of vertigo, 15% of patients were found to have profound sensorineural hearing loss, and 97% of patients had radiological findings suggestive of fistula.[4]

Evaluation

Diagnosing labyrinthine fistulas can be difficult. Diagnostic criteria are not well established. There are criteria suggested by the Intractable Hearing Loss Research Committee of the Ministry of Health and Welfare (revised 2016).[1] These include:

1. Symptoms - Tinnitus, aural fullness, hearing impairment, and vestibular symptoms that are associated with pre-existing or coexisting middle ear or inner ear disease/surgery
2. Lab findings - Biochemical tests, microscopic/endoscopic inspection
3. References - Cochlin-tomoprotein detection test, beta2 transferrin, idiopathic
4. Differential diagnosis - other known causes of inner ear diseases
5. Definite diagnosis - Perilymph-specific protein detection, explorative tympanotomy (ET)

A complete assessment of auditory acuity, including auditory brainstem response (ABR), emission testing, and pure tone audiometry should be done to assess hearing loss.[8] A computed tomography (CT) scan is the most reliable method for the diagnosis of labyrinthine fistulas preoperatively. Pneumolabyrinth seen on a CT scan confirms the diagnosis and indicates the need for urgent surgical intervention.[5] However, when the pneumolabyrinth is small, visualization on CT can be challenging. Therefore, getting coronal views of the temporal bone to the superior semicircular canals would aid in the diagnosis.[5] Definitive diagnosis can only be achieved with exploratory tympanotomy (ET).

Treatment / Management

There is currently no consensus on optimal surgical management of labyrinthine fistulas.[3] Goto et al. came to the conclusion that urgent tympanotomy was not required due to poor results with hearing recovery.[7] Seltzer and Mccabe, however, found that hearing improvement was possible after many years of having symptoms in patients that had a perilymphatic repair.[7] This suggests that early surgical intervention may be important for eventual hearing recovery. Corticosteroids given intravenously during surgery have been associated with the improvement of postoperative hearing. Obliteration of the mastoid also has been shown to improve postoperative dizziness in some patients.[3]

Because of a lack of definitive diagnostic criteria, conservative management is preferred initially with head elevation, bed rest, and avoiding activities that would increase intracranial pressure and straining. If symptoms persist or are recurrent, exploratory tympanotomy is the next step. Surgery has been shown to often improve dizziness and vertigo, but rarely improved hearing loss with increased risk of iatrogenic sensorineural hearing loss.[3][7]

Management of labyrinthine fistulas induced by cholesteatomas includes complete removal of the cholesteatoma matrix from the fistula and subsequent closure of the fistula.[3] Resurfacing of the horizontal semicircular canal is preferred to "plugging" as this leads to canal function loss with increased risk of hearing loss. Similar to other causes of perilymphatic fistulas, surgical treatment does seem to have better outcomes with vestibular symptoms rather than auditory symptoms.

Differential Diagnosis

Differential diagnoses include:

• Meniere syndrome (primary endolymphatic hydrops) - Meniere's disease is much more common than perilymphatic fistula and can present with all the symptoms of perilymphatic fistula.
• Secondary endolymphatic hydrops - can occur from head trauma, allergies, or underlying issues such as an autoimmune disorder.[9][3]
• Acoustic neuromas
• Hemorrhagic stroke
• Superior semicircular canal dehiscence

Prognosis

Surgical intervention has been shown to improve symptoms of vertigo and dizziness the most. If hearing loss is present, surgical intervention may or may not improve hearing function.[7] There is, however, some evidence showing that prognosis and improvement of symptoms are based on the severity of inciting events and the severity of symptoms at the onset.[7] The more severe the symptoms or inciting events, the less likely spontaneous healing or surgical intervention, will be of benefit. Improvement in hearing from perilymphatic fistulas was reported to only be around 9% to 17% from the data collected by Goto et al. and Black et al.[7]

Complications

The most common complications of a labyrinthine fistula are hearing loss and vertigo. Complications are also seen in post-surgical fistula repairs. These include tympanic membrane ruptures, postoperative hearing loss, and chorda tympani injuries.[10] Postoperative hearing loss and chorda tympani injury have resolved in some patients after a few months.[11] 

Superior canal dehiscence syndrome can also arise as a complication, which is believed to be a variant of the fistula, but not caused by a true fistula (rather a communication between the superior bony canal and middle cranial fossa), may cause some unique phenomena, such as hearing one’s own voice, heartbeat, and eye movements. Pressure changes induced by performing a Valsalva maneuver with pinched nostrils (or otherwise straining) may provoke nystagmus and/or oscillopsia and vertigo.