Perilymph Fistula
Timothy C. Hain, MD
Content last edited: 3/21/2002
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Figure 1. Anatomy of the inner and middle ear. A fistula is an abnormal connection between the air-filled middle ear and the fluid filled inner ear. The two weakest points are membranes located at the stapes footplate (the "oval window"), #4 here, and just below, a small niche called the "round window".
There can also be fistulae at other points, but they require erosion of bone.
A dehiscence is similar to a fistula, but not as severe as there is generally no active leakage. Bone is missing, uncovering a membrane.
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What is a Perilymph Fistula?
- Round window
- Oval Window
- Otic capsule
- Superior canal dehiscence syndrome
- Cholesteatoma
- Fenestration
- Temporal bone fracture
- Micro-fissure
A perilymph fistula (PLF) is a an abnormal opening between the air-filled middle ear and the fluid-filled inner ear. In most instances it is a tear or defect in one or both of the small, thin membranes between the middle and inner ears. These membranes are called the "oval window" and the "round window." Figure 2 illustrates a round-window fistula.
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Figure 2. Round window fistula. An opening in the round window allows perilymph to leak out into the middle ear. In this artist's depiction, for clarity, bone is not shown between the middle and inner ears. While it is difficult to be sure, it seems likely that in most cases there is only a small oozing of fluid between the perilymphatic space and the air-filled middle ear. |
Another possible location for a fistula is in the bone of the ear (the otic capsule). This is a rare condition where the bone between the ear and brain area is missing or thin, causing symptoms very similar to that of a round or oval window fistula. The most common type is located just above the superior semicircular canal (see figure 1) and is called the superior canal dehiscence syndrome (Minor et al, 1998; Minor 2000). Roughly 2% of persons at autopsy are found to have thinning of bone in this location, which is thought to predispose them to this syndrome (Carey et al, 2000). Eye movements in this syndrome align with the superior canal (Cremer et al, 2000).
Another type of bony fistula is the situation after a surgery is done called fenestration (previously done for otosclerosis; this procedure is no longer used). This is a less severe situation than the oval or round window fistuale, as inner ear fluid is generally not in direct communication with an air-filled cavity, but a membrane is present which maintains a seal. In the first case, the roof of the superior canal is missing. In the second, there is an opening between the lateral semicircular canal and an artificially created cavity in the mastoid sinus area. In either of these conditions, pressure in the ear or loud noises can cause strong vertigo and jumping of the eyes (nystagmus).
In the past, a condition called cholesteatoma was a common cause of this problem also, but this condition is now encountered only rarely because of improved antibiotic treatments. It is possible that there are occasionally fistulae associated with tiny cracks in the bone between the middle and inner ear.
A closely related condition is alternobaric vertigo (Wicks, 1989). Here dizziness is associated with a difference in pressure between ears. This condition remains difficult to document. An example of this might be vertigo appearing while flying in an unpressurized airplane in someone who could "pop" their ear on one side, but not on the other.
Whatever the cause, PLF is a very rare condition compared to most other causes of dizziness and hearing loss.
What are the Symptoms of a Perilymph Fistula?
- Dizziness
- Hearing symptoms (tinnitus, hearing loss)
- Pressure sensitivity
- Tullio's phenomenon (sensitivity to loud noises)
The symptoms of perilymph fistula may include hearing loss, dizziness, vertigo, imbalance, motion intolerance, nausea, and vomiting. Usually patients report an unsteadiness which increases with activity and which is relieved by rest. Some people experience ringing or fullness in the ears, and many notice a hearing loss. These symptoms are somewhat nonspecific and overlap with other inner ear disorders, notably Ménière's disease.
Pressure sensitivity is a symptom that is common in fistula, but uncommon in other inner ear disorders. Natural changes in air pressure that occur in the middle ear (for example, when your ears pop in an airplane) normally do not affect your inner ear. When a fistula is present, changes in middle ear pressure may directly affect the inner ear, stimulating the balance and/or hearing structures and causing typical symptoms. Thus, some people with fistulae find that their symptoms get worse with coughing, sneezing, or blowing their noses, as well as with exertion and activity. Similarly, people may reliably become dizzy after descent in an airplane, due to pressure fluctuations in the cabin. This sort of symptom goes under the general rubric of Valsalva induced dizziness, and it can also be associated with other medical conditions in entirely different categories --for example, the Chiari malformation, and a heart condition called idiopathic hypertensive sub-aortic stenosis (IHSS). There are a number of other inner-ear conditions that can also cause pressure sensitivity, such as Ménière's disease and vestibulofibrosis.
Another unusual symptom that may be found in persons with a fistula, particularly the "superior canal dehiscence" variant, is that use of ones own voice or a musical instrument will cause dizziness (this is called the Tullio's phenomenon). This symptom can also be found in Meniere's disease and vestibulofibrosis.
What Causes a Perilymph Fistula?
- Head injury or ear surgery
- Pressure trauma
- Congenital
- Infection
Head trauma is the most common cause of fistulae, usually involving a direct blow to the ear. Fistulae may also develop following rapid or profound changes in intracranial or atmospheric pressure, such as may occur with scuba diving. Forceful coughing, sneezing or straining as in lifting a heavy object may rarely cause a fistula. Ear surgery, particularly stapes surgery, often causes fistula. Some patients develop symptoms attributed to fistula following airplane decent. Fistulae may be present from birth (usually in association with deafness) or may result from chronic ear infections called cholesteatomas.
Fistulae are also created by a surgical procedure usually done for otosclerosis (stapedectomy). A dehiscence was the intended result of another surgical procedure for otosclerosis called a fenestration. Pathologically, fistulae have been reported in parts of the bone of the otic capsule other than the canals or window areas. Their significance is controversial. Fistulae are usually associated with some event, most commonly barotrauma or head injury (Lehrer et al, 1984), but rarely, fistulae occur spontaneously (Kohut, 1996). Fistulae may occur in one or both ears, but bilateral fistulae are thought to be exceedingly rare.
How is a Perilymph Fistula Diagnosed?
Certain rare fistulae due to tumor or bone defects (such as superior canal dehiscence) are relatively easy to diagnose because they can be seen on magnetic resonance imaging (MRI) or computerized tomography (CT) scan. However, for the others, there is considerable controversy about how to make the diagnosis. Ménière's disease, which is much more common than fistula, can have identical symptoms, including pressure sensitivity. For this reason, fistula diagnoses made in patients without barotrauma are easily questioned. A second problem is that at the time of surgery, diagnosis is entirely based on the surgeon's judgment, and these judgments have been variable. In non-emergency cases, especially where there has been no barotrauma, we think it is prudent to get two opinions prior to proceeding with surgical remedies. A diagnosis of fistula is particularly likely to be incorrect in situations where there is no reasonable cause, or when bilateral fistula is diagnosed.
The following tests are recommended when fistula is strongly suspected:
- Fistula test
- Valsalva test (see below)
- Audiometry
- Electrocochleography (ECOG)
- ENG
- Temporal bone CT scan, high resolution
- MRI scan
A fistula test, which entails making a sensitive recording of eye movements while pressurizing each ear canal with a small rubber bulb, will almost always be needed. A positive test is good grounds for surgical exploration. In window fistulae, very little nystagmus (jumping of the eyes) is produced, and a positive test may consist of only a slight nystagmus after pressurization. In superior canal dehiscence, a strong nystagmus may be produced.
In the Valsalva test, positive pressure or Valsalva against pinched nostrils produces downbeating nystagmus, with a torsional fast phase consistent with stimulation of the affected ear (counterclockwise for right ear, clockwise for left ear). Negative pressure or Valsalva against a closed glottis may produce upbeating nystagmus and nystagmus beating with the torsional fast phase in the opposite direction (clockwise for right ear, counterclockwise for left ear). For those familiar with BPPV, the vector relationships between vertical and torsional components is reversed so that the upbeating nystagmus beats away from the "bad" ear, and downbeating, towards the "good" ear. Not infrequently however, no nystagmus at all is produced by either maneuver.
Audiometry and an ENG are nearly always necessary in order to establish the side, and to exclude other potential causes of symptoms. Audiometry may show a sensorineural hearing loss. In patients with sickle cell disease (SCD), audiometry may show bone conduction scores better than air (conductive hyperacusis).
An "ECOG", or electrocochleography may be of help also, although only in rare instances. The main role of ECOG is to diagnose Ménière's disease, which is a common alternative source of pressure sensitivity. ECOG is technically challenging and it may be difficult to locate a laboratory that does it.
An MRI and/or a temporal bone CT scan is usually helpful to exclude other possibilities. CT of the temporal bone is very accurate in identifying canal fistulae (Fuse et al, 1996), although as there is really no other good way to identify canal fistulae, it is hard to be sure that it is picking them all up. CT of the temporal bone should be done with at least 1 mm resolution. Ideally, the cuts should be in the plane of the canal in which one suspects a leak. At this writing (3/2002), temporal bone CT scans protocols for this purpose, especially to diagnose superior canal dehiscence, are not widely available and one may need to go to one of a few specialized centers around the country to get this done properly.
MRI is not the best test for fistulae because it does not show the bone, and because the resolution is not as good as CT scan. However, MRI is the best way of showing other possibly confounding problems, such as tumors or multiple sclerosis plaques. We usually recommend an MRI prior to considering fistula surgery.
When a fistula is especially severe, it may result in a CSF leak, as the perilymph of the inner ear is contiguous with spinal fluid. CSF leaks mainly are a consequence of head injury or surgery (for example, they are fairly common after acoustic neuroma surgery). There are some special purpose tests for CSF leaks. CSF leaks can be documented by CT cisternography with a spinal injection of a contrast material. The head is tilted down for three minutes with the patient prone, and a CT scan is done with high resolution cuts (spiral), in the coronal plane immediately after the prone positioning, to cover the frontal sinus through the mastoid sinus region.
Although rarely encountered, as it requires a very large fistula and a rapid CT scan of the ear, air in the labyrinth (pneumolabyrinth) is the most convincing finding of fistula. Middle ear effusions may also be suggestive of fistula. Variants in the stapes structure are sometimes a clue that there is a congenital fistula at the level of the oval window.
Round window fistulae are generally unaccompanied by CT abnormalities, although an effusion would seem to be possible in this situation. Other congenital abnormalities of the cochlea, vestibule, and vestibular aqueduct may also be documented by CT of the temporal bone (Swartz and Harnsberger, 1998). Unfortunately, these procedures are not 100% accurate for all types of fistulae, and in some cases, only direct inspection of the inner ear will confirm or rule/out a possible fistula.
Investigational tests for Fistulae
Recently, sound evoked vestibulocollic evoked potentials, called the VEMP test (vestibular evoked myogenic potential) have been described as useful in diagnosing Tullio's phenomenon from superior canal dehiscence (Brantberg et al, 1999; Watson et al, 2000). VEMP's resemble an instrumented Tullio test -- potentials are larger due to sound-sensitivity of the inner ear (saccule). This test is still considered investigational and it is not well normed at this writing (3/2002). It also may be difficult to locate a laboratory that does it.
Endoscopy is another method of documenting a fistula without an operation. The technique is to inject a fluorescent material that gets into the perilymph, and observe it with an endoscope (Kleeman et al, 2001). There are several difficulties. First, getting the dye into the perilymph may be problematic. While perilymph is connected to some extent to CSF, the connection is not as open in some people as in others. Injection of dye into other fluids, such as intravenously, leaves open the question as to whether the fluid seen that fluoresces is serum or perilymph. The test also involves a subjective judgement, which has been problematic in other contexts. This procedure is not widely available.
Questionable Tests for Fistulae
There are several tests for fistula that we do not think are necessary or reliable. The pressure posturography testis one -- this test involves measuring postural sway after pressurization of the ear. This test appears to us to be prone to false positives. The glycerin test has also been advocated for fistula (Leherer, 1980). We are concerned that this test is diagnosing Ménière's disease rather than fistula.
How is a Perilymph Fistula Treated?
Conservative Approach
Before we begin, note that these recommendations are not based in much evidence. In general, they reflect physician's guesses as what might be good or bad to do. They rarely reflect evidence in the sense of a controlled trial.
Based on exeperience in surgically created fistulae (i.e. stapes surgery), it is thought that in many cases, a window fistula will heal itself if activity is restricted. In such cases, strict bed rest is recommended for one week or more to give the fistula a chance to close. It is usual to wait six months before embarking on surgical repair, given that hearing function is reasonable and is stable or improving. With respect to air travel, while it is certainly safest to avoid air travel altogether, in some instances it may be unavoidable. In this case, we suggest using a nasal decongestant at least one half hour prior to landing. Some of our patients have indicated that ear plugs are helpful in this situation also. Occasionally a ventilation tube will help.
Patients with a presumed fistula should probably avoid the following:
- Lifting
- Straining
- Bending over
- Popping the ears
- Forceful nose blowing
- Air pressure changes such as due to air travel
- High speed elevators
- Scuba diving
- Loud noises (such as your own singing or a musical instrument)
Surgery
If you have an otic capsule fistula, if your symptoms are significant and have not responded to the conservative approach outlined above, or if you have a progressive hearing loss, surgical repair of the fistula may be required. For otic capsule fistulae involving a canal, surgery generally involves plugging of the canal.
For a window fistula surgery involves placing a soft-tissue graft over the fistula defect in the oval and/or round window. Otic capsule fistula do not, in general, heal by themselves. Unfortunately, in our opinion, surgical procedures for window fistulae are not well worked out. Patients are often reoperated when it is decided that the graft has failed. In most instances, shunt of the endolymphatic sac or spinal fluid pathways (for example, lumbar shunts) are not appropriate treatments for fistulae.
For persons with symptoms mainly induced by flying, after conservative measures have failed, a ventilation tube may be worth considering.
Medications
For persons with plugged up eustachian tubes (such as due to a cold or allergy), decongestants, allergy medication, and ventilating tubes may be of use. Medications in the minor tranquilizer family such as diazepam (Valium), klonazepam and lorazepam help some individuals. Antivert and phenergan are also medications which some find helpful.
How Might a Perilymph Fistula Affect My Life?
You may find that modifications in your daily activities will be necessary so that you can cope with your dizziness. For example, you may need to have someone shop for you for a while if going up and down supermarket aisles tends to increase your symptoms. See also suggestions above under "conservative treatment".
You should take special precautions in situations where clear, normal vision is not available to you. For example, avoid trying to walk through dark rooms and hallways; keep lights or nightlights on at all times. Do not drive your car at night or during stormy weather when visibility is poor.
Make sure your hallways at home are uncluttered and free of obstructions. Most important, do not place yourself in a situation where you might lose your balance and be at risk for a fall and serious injury; stay off of chairs, stools, ladders, roofs, etc. If your balance continues to be a serious problem, you may need to consider using a cane or walker for added safety.
Research Studies in Perilymph fistulae
At the American Hearing Research Foundation (AHRF), we have funded basic research on perilymph fistula in the past. Click here if you would you would like more information about contributing to the AHRF's efforts.
Acknowledgments
Figures 1 and 2 are courtesy of Northwestern University.
References
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