Timothy C. Hain, MD Return to Index. Please read our disclaimer. Search this site. Content last updated: 11/25/2000
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. Bone is missing over the top (superior) semicircular canal, uncovering a membrane. This dehiscence makes the ear more sensitive to pressure and noise.
A perilymph fistula, or PLF, is an abnormal opening in fluid filled inner ear. There are several possible places that there can be an opening-- betwen the the air-filled middle ear/mastoid sinus, into the intracranial cavity, or into other spaces in the temporal bone. 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. 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 an abnormal communication is in the bone of the ear (the otic capsule). An example of this would be the so-called "superior canal dehiscence" syndrome (Minor et al, 1998; Minor 2000), and 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 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 artifically created cavity in the mastoid sinus area. In either of these conditions pressure in the ear or loud noises which can cause strong vertigo and jumping of the eyes (nystagmus). Fistulae can also occur as a late complication of mastoid surgery using the canal wall down technique. In this instance, the fistula is caused by repeated infections in the opened mastoid. (Hakuba et al, 2002)
In years gone by, a condition called "cholesteatoma" was a common cause of this problem also, but this condition is now encountered only rarely becasuse 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.
Whatever the cause, PLF is a very rare condition compared to most other causes of dizziness and hearing loss.
The 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 will directly affect the inner ear, stimulating the balance and/or hearing structures within and causing typical symptoms. There are a number of other conditions that can also cause pressure sensitivity such as Meniere's disease and vestibular fibrosis.
The symptoms of perilymph fistula may include dizziness, vertigo, imbalance, nausea, and vomiting. Usually however, 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. Some people with fistulas find that their symptoms get worse with coughing, sneezing, or blowing their noses, as well as with exertion and activity. 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 "IHSS". Returning to fistula, it is not unusual to notice that use of ones own voice or a musical instrument will cause dizziness (this is called the "Tullio's phenomenon").
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.
Head trauma is the most common cause of fistulas, usually involving a direct blow to the ear. Fistulas 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. Fistulas may be present from birth (usually in association with deafness) or may result from chronic ear infections called "cholesteatomas".
A closely related condition is a "dehiscence". Rarely the bone between the ear and brain area is missing or thin, causing symptoms very similar to that of a fistula. This is called the superior canal dehiscence syndrome). Roughly 2% of persons at autopsy are found to have thinning of bone, which is thought to predispose them to this syndrome (Carey et al, 2000). Eue movements in this syndrome align with the superior canal (Cremer et al, 2000).
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).
Fistulas may occur in one or both ears, but bilateral fistulas are thought to be exceedingly rare.
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 MRI or CT scan. However, for the others, there is considerable controversy about how to make the diagnosis. Meniere'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 judgement, and these judgements 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 proceding with surgical remedies. Situations where the diagnosis of fistula is likely to be incorrect is that where fistula is diagnosed without a reasonable cause, and a diagnosis of bilateral fistula.
Tests recommended when fistula is strongly suspected:
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 is produced, and a positive test may consist only of a slight nystagmus after pressurization. In superior canal dehiscence, a strong nystagmus may be produced.
Positive pressure or Valsalva against pinched nostrils produces downbeating nystagmus, with a torsional fast phase consistent with stimulation of the affected ear (CCW for right ear, CW for left ear). Negative pressure or Valsalva against a closed glottus may produce upbeating nystagmus and nystagmus beating with the torsional fast phase in the opposite direction (CW for right ear, CCW 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" is 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 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 Meniere'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. CTof 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 should be done of the temporal bone 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 (6/2000), temporal bone CT scans protocols for this purpose, especially to diagnose superior canal dehiscense, 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 doesn't show the bone and 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.
A CSF leak can occur from the ear as well as from other places in the head. CSF leaks mainly are a consequence of head injury or surgery (for example, they are fairly common after acoustic neuroma surgery). CSF leaks can be documented by CT cisternography with a spinal injection of a contrast material. The head is tilted down for 3 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.
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 congential 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.
Recently sound evoked vestibulocollic evoked potentials have been described as useful in diagnosing Tullio's phenomenon from superior canal dehiscence (Brantberg et al, 1999; Watson et al, 2000). These are also called "VEMP" for vestibular evoked myogenic potential. This test is still considered investigational and it may be difficult to locate a laboratory that does it.
A method of documenting a fistula without operation is to inject a fluorescent material that gets into 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. This procedure is not widely available.
There are several tests for fistula which we do not think are necessary or reliable. The pressure posturography test is 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 Meniere's rather than fistula.
Conservative approach: In many cases, a window fistula fistula will heal itself if your 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 6 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.
Surgery: If you have a canal 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 canal fistulas, 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 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 (e.g. lumbar shunts) are not appropriate treatments for fistulae.
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.
A trial of bed rest for 1-2 weeks may be recommended. In this situation, one attempts to minimize pressure changes in the ear, hoping that scar tissue will seal the leak. For persons with superior canal dehiscence, no treatment will close the bone, so the only reasonable options are avoidance and surgery.
Ear plugs are sometimes helpful for those who develop dizziness related to loud noise or rapid fluctuation in air pressure. Custom ear plugs, such as the ER/15 which seal the affected ear seem to work the best.
Surgery may be recommended to close the leak. If hearing is good, or the diagnosis not that clear, most persons are advised to wait for 6 months before proceeding with a surgical exploration. The hope is that the body will repair the leak on its own. This is a reasonable hope, as most fistulas do indeed appear to close spontaneously. On the other hand, if in the judgement of your doctor, hearing appears to be at risk, then surgery may be advised more quickly.
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.
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. Don't 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.
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Acknowledgement: Figures 1 and 2 are courtesy of Northwestern University.
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