Laboratory Studies

No laboratory studies are relevant to the diagnosis of perilymphatic fistula (PLF). A possible future role for beta2-transferrin assay is discussed in Intraoperative details.

A stable perilymph specific protein, Cochlin-tomoprotein has been characterized at the Nippon Medical School in Tokyo. Western blot assays revealed that Cochlin-tomoprotein is present in all perilymph samples and reliably absent in nonperilymph samples (specifically 98.2%).^{[17, 18]}

Imaging Studies

Obtain gadolinium-enhanced MRI scans in all individuals with unilateral otologic symptoms to exclude acoustic neuroma or other structural lesions of the cerebellar pontine angle or neuraxis.

The incidence of perilymphatic fistula (PLF) is much higher in individuals with congenital deformities of the otic capsule. Consequently, a nonenhanced fine-cut CT scan of the temporal bones can be helpful, especially in children. A child with progressive or sudden sensorineural hearing loss in an ear that is incompletely developed has a much higher risk of perilymphatic fistula (PLF) than a child with normal inner ear radiographic morphology.

A retrospective study by Venkatasamy et al indicated that assessment with a combination of CT scanning and MRI can quickly and accurately diagnose perilymphatic fistula (PLF), with the combined modalities having a sensitivity of over 80%. Using CT scanning/MRI, fluid filling of the window niches was reportedly the most reliable sign of the condition, with, for the round and oval windows, sensitivity being 83-100% and 66-83%, respectively, and specificity being 60% and 91-100%, respectively.^[19]

Audiography

Obtain an audiogram in all patients with otologic symptomatology. Sensorineural hearing loss is a regular feature of perilymphatic fistula (PLF), but any pattern of sensorineural hearing loss can result from perilymphatic fistula (PLF). Because it is otherwise relatively uncommon, low-frequency hearing loss is perhaps a bit more suggestive of perilymphatic fistula (PLF); however, mid-frequency, high-frequency, and flat losses are also consistent with the diagnosis. Fluctuating hearing loss is common with perilymphatic fistula (PLF), as it is with Ménière’s disease.

Some authors have reported a conductive loss in patients with perilymphatic fistula (PLF), but this probably represents a small percentage of patients.

Electrocochleography

ECoG is a method of measuring intracochlear electrical potential changes associated with hearing. Three separate responses can be obtained, as follows:

The cochlear microphonic is a stimulus-related alternating current (AC) potential that closely mimics the stimulus and therefore is difficult to separate from stimulus artifact. The technique used to produce standard electrocochleographic tracings eliminates the cochlear microphonic from the ECoG tracing.
The summating potential (SP) is a stimulus-related direct current (DC) potential that reflects the time-related displacement of the cochlear partition. The SP has been shown to be sensitive to inner ear fluid imbalance, particularly in Ménière disease and perilymphatic fistula (PLF).
The action potential is an AC potential that represents the compound action potential of the fiber's eighth nerve that discharges synchronously in response to a stimulus. The initial portion of the action potential also is known as wave I of the ABR.

The two methods of recording ECoG are transtympanic and extratympanic.

Transtympanic: A needle electrode passed through the tympanic membrane that rests on the promontory provides the largest and most easily readable tracings because it is a near-field potential. Fewer signals need to be averaged to obtain an interpretable response, and the potentials are much longer than in other methods of ECoG. Acceptance of transtympanic ECoG has been limited because it can be painful and because a physician's presence is required to pass the electrode through the tympanic membrane.
Extratympanic: Extratympanic ECoG is comfortable and noninvasive, and it can be performed in a nonmedical setting. However, the size of the reported potentials is significantly smaller than with transtympanic ECoG, and, consequently, the reported potentials are more difficult to identify and interpret.

ECoG is useful in the diagnosis of both Ménière disease and PLF. Both conditions produce an elevated SP/AP ratio. Increase in the SP/AP ratio appears to result because of enlargement of the SP component in patients with Ménière disease. The mechanism by which it increases in perilymphatic fistula (PLF) is controversial. Some authors believe that the increase in SP/AP ratio in patients with perilymphatic fistula (PLF) may be the consequence of a decrease in the AP.

Several guinea pig studies have shown consistent increases in the SP/AP ratio in guinea pigs with artificially induced perilymphatic fistulas (PLFs). Gibson has demonstrated an increase in the SP/AP ratio during stapedectomy.^[20]The creation of a control hole in the footplate is not sufficient to produce a change in the SP/AP ratio; a change is noted only after some perilymph has been removed from the vestibule. Meyerhoff and Yellin have demonstrated that in individuals with surgically proven perilymphatic fistulas (PLFs) who have elevated SP/AP ratios preoperatively, the SP/AP ratio reliably returns to normal after surgical repair of the fistula.^[21]

Fistula test

Fistula testing has been shown to yield positive results in patients with perilymphatic fistula (PLF). The application of positive pressure to a tympanic membrane in an ear with a fistula is known to possibly produce nystagmus. The production of nystagmus secondary to positive pressure is referred to as a positive fistula test result. The definition actually requires the presence of documentable nystagmus. The reproduction of symptomatology secondary to positive pressure may have diagnostic importance but does not constitute a positive fistula test.

An objective record of fistula testing can be made using the electronystagmogram (ENG) and the impedance bridge. To accomplish this, the emittance probe is placed into first one ear and then the other. The pressure in the external auditory canal is varied between +200 and -200 mm of mercury. The ENG has been examined for induced nystagmus. Each ear is tested separately. A positive fistula result is identified by the production of nystagmus associated with a change in pressure on the tympanic membrane. In some cases, the nystagmus can be seen to change direction as the pressure changes from positive to negative. One would expect that the patient's subjective symptoms of vertigo, with or without nausea, would be induced during the presence of nystagmoid eye movements in a positive test result. The results of the ENG fistula test then can be compared to platform fistula test results.

Dynamic platform posturography

This test can be used to generate a sensitive test for perilymphatic fistula (PLF). In dynamic platform posturography, pressure is applied to the external auditory canal. The increase or decrease in pressure is transmitted to the tympanic membrane middle ear space and, if a fistula is present, to the inner ear. When perilymphatic fistula (PLF) is present, abnormal sway is generated by these pressure changes. Using the acoustic impedance bridge to quantify changes in external auditory canal pressure and the dynamic platform posturography to quantify anterior, posterior, and lateral sway in response to such pressure changes, a sensitive assessment for perilymphatic fistula (PLF) can be developed. Several studies have demonstrated that patients with positive results from platform fistula testing have a high likelihood of having perilymphatic fistula (PLF).

Vestibular-evoked myogenic potential (VEMP) testing

VEMP testing is a newer diagnostic tool to evaluate patients with vestibular disorders. During VEMP testing, a suprathreshold sound is administered to the test ear. Relaxation potentials of the ipsilateral sternocleidomastoid muscle are measured and quantified. In individuals with normal hearing and vestibular function, the VEMP threshold to sounds is from 90-105 dB HL. In patients with superior canal dehiscence or perilymphatic fistula, the thresholds may be decreased to as low as 70 dB HL. Decreased VEMP thresholds with a history and symptoms suggestive of a perilymphatic fistula can provide further evidence of the presence of a fistula.^[22]

Diagnostic Procedures

Poe et al performed middle ear endoscopy in 20 patients with suggested perilymphatic fistula (PLF).^[23]They failed to demonstrate fistulas in any patient but placed autologous blood patches in 8 patients around the round and oval windows. No change in hearing was noted postoperatively, but 3-4 patients with preoperative vertigo had relief of symptoms, and 2-3 patients with preoperative positive fistula test results had negative test results postoperatively.

The most troublesome difficulty described by Poe was obscured vision of the oval window and round window niche, secondary to mucosal adhesions. The average human ear contains only 0.07 mL (70 mcL) of perilymph; therefore, even relatively rapid leaks are, in absolute terms, quite small. Even with magnification, leaks involving only 5-10% of the perilymph are difficult to see in an operative field because local anesthetics have been injected, irrigating fluids have been used, and a minimal amount of bleeding may be present.

Garg and Djalilian reported resolution of symptoms in two of three patients with presumed traumatic perilymphatic fistulas after intratympanic injection of blood into the middle ear space.^[24]

Treatment & Management

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Author

Joe Walter Kutz, Jr, MD, FACS Associate Professor, Associate Residency Director, Neurotology Fellowship Director, Department of Otolaryngology–Head and Neck Surgery, University of Texas Southwestern Medical Center at Dallas, Southwestern Medical School

Joe Walter Kutz, Jr, MD, FACS is a member of the following medical societies: Alpha Omega Alpha, American Academy of Otolaryngology-Head and Neck Surgery, American Neurotology Society, Otosclerosis Study Group, Texas Medical Association, Triological Society

Disclosure: Received income in an amount equal to or greater than $250 from: Alcon; Medtronic; Eloxx; Acclarent.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Gerard J Gianoli, MD Clinical Associate Professor, Departments of Otolaryngology-Head and Neck Surgery and Pediatrics, Tulane University School of Medicine; President, The Ear and Balance Institute; Board of Directors, Ponchartrain Surgery Center

Gerard J Gianoli, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American College of Surgeons, American Neurotology Society, American Otological Society, Society of University Otolaryngologists-Head and Neck Surgeons, Triological Society

Disclosure: Nothing to disclose.

Chief Editor

Arlen D Meyers, MD, MBA Professor of Otolaryngology, Dentistry, and Engineering, University of Colorado School of Medicine

Arlen D Meyers, MD, MBA is a member of the following medical societies: American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, American Head and Neck Society

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Cerescan; Ryte; Neosoma; MI10<br/>Received income in an amount equal to or greater than $250 from: Neosoma; Cyberionix (CYBX)<br/>Received ownership interest from Cerescan for consulting for: Neosoma, MI10.

Additional Contributors

Michael E Hoffer, MD Director, Spatial Orientation Center, Department of Otolaryngology, Naval Medical Center of San Diego

Michael E Hoffer, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery

Disclosure: Received royalty from American biloogical group for other.

Peter S Roland, MD Professor, Department of Neurological Surgery, Professor and Chairman, Department of Otolaryngology-Head and Neck Surgery, Director, Clinical Center for Auditory, Vestibular, and Facial Nerve Disorders, Chief of Pediatric Otology, University of Texas Southwestern Medical Center; Chief of Pediatric Otology, Children’s Medical Center of Dallas; President of Medical Staff, Parkland Memorial Hospital; Adjunct Professor of Communicative Disorders, School of Behavioral and Brain Sciences, Chief of Medical Service, Callier Center for Communicative Disorders, University of Texas School of Human Development

Peter S Roland, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Otolaryngic Allergy, American Academy of Otolaryngology-Head and Neck Surgery, American Auditory Society, American Neurotology Society, American Otological Society, North American Skull Base Society, Society of University Otolaryngologists-Head and Neck Surgeons, The Triological Society

Disclosure: Received honoraria from Alcon Labs for consulting; Received honoraria from Advanced Bionics for board membership; Received honoraria from Cochlear Corp for board membership; Received travel grants from Med El Corp for consulting.