Fistula test or Perilymphatic fistula test : The fistula test is performed by applying positive and negative pressure to the intact eardrum using a pneumatic otoscope or by pressing tragus.
Used to detect Perilymph fistula.
|Positive Result(indicates Perilymphatic Fistula)||Negative Result(Normal)|
|when positive pressure is applied with the pneumatic otoscope||when positive pressure is applied with the pneumatic otoscope |
Onset of Nystagmus towards ipsilateral ear.
|No changes noted.|
|when negative pressure is applied with the pneumatic otoscope||when positive pressure is applied with the pneumatic otoscope |
Nystagmus also reverses & changes its direction towards contralateral ear.
|No changes noted.|
The type of nystagmus seen can be deducted from the picture below.
Ok first let me try to explain you the figure given above.
First lets take a normal person as an example ,in him when,
|SCC which is stimulated||This will be the direction of slow phase of nystagmus in ear with fistula|
|right horizontal semicircular canal is stimulated||it causes movement of both eyes towards the opposite(left) side.|
|right posterior semicircular canal is stimulated||it causes downward movement of both eyes as well as intorsion of right eye& extorsion of left eye.|
|right anterior semicircular canal is stimulated||it causes upward movement of both eyes as well as intorsion of right eye& extorsion of left eye.|
|Now lets come to left vestibular system|
|left horizontal semicircular canal is stimulated||it causes movement of both eyes towards the opposite(right) side.|
|left posterior semicircular canal is stimulated||it causes downward movement of both eyes as well as intorsion of left eye& extorsion of right eye.|
|left anterior semicircular canal is stimulated||it causes upward movement of both eyes as well as intorsion of left eye& extorsion of right eye.|
So, if there is fistula in right ear,then
|if fistula on right horizontal SCC(that means when positive pressure is applied, the right horizontal SCC will get stimulated)||when positive pressure applied via pneumatic otoscope causes slow component of nystagmus towards opposite ear . |
As per convention direction of nystagmus is towards fast component, therefore we say that nystagmus is towards ipsilateral ear.
|if fistula on right posterior SCC||when positive pressure is applied to right ear, then according to the diagram we see that it will cause nystagmus with slow component towards downside& intorsion of eyeball. |
As per convention direction of nystagmus is towards fast component, therefore we say that the nystagmus is upbeating& extorion type.
A perilymph fistula (PLF) is an abnormal opening between the air-filled middle ear and the fluid-filled inner ear. It may occur due to a defect in one of three locations:
- Oval Window –(most common site)
- Stapedectomy surgery (for otosclerosis)
- Head trauma or barotrauma (pressure injury)
- Acoustic trauma
- Round window -
- Barotrauma -- SCUBA diving, airplane pressurization
- Congenital malformations (such as Mondini dysplasia)
- Otic capsule--
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. Problems in the otic capsule that may cause a perilymph fistula include:
- Superior canal dehiscence syndrome (anterior SCC)
- Fenestration -Another type of bony fistula can occur after a surgical procedure called fenestration previously done for otosclerosis;
- Temporal bone fracture
The most common type of otic capsule fistula is located just above the superior semicircular canal and is called the superior canal dehiscence syndrome.
|False positive fistula test(Hennebert sign)||False negative fistula test|
|Congenital syphilis |
(here stapes footplate is hypermobile, so even small pressure changes in ear, cause excessive movement of stapes footplate & excessive stimulation of utricular macule)
|In Dead ear ( inner ear is damaged), there will be NO response even if a Perilymphatic fistula exists.|
|25% cases of Meneire’s disease. |
(here in 25% cases of meniere’s ,fibrous bands form connecting to utricular macule to stapes footplate)
|Also seen when cholesteatoma covers the site of fistula & doesn’t allow pressure changes to be transmits to labyrinth.|
- It is a false positive fistula test i.e, when there is no evidence of middle ear disease causing fistula of horizontal semicircular canal.
- It is seen in 25% cases of meniere's disease or congenital syphilis.
- Hennebert sign- pressure induced nystagmus &
- Hennebert symptom- pressure induced dizziness.
Sound-induced vestibular symptoms such as vertigo, nystagmus, oscillopsia, and postural imbalance .
Tullio's phenomenon is seen mainly in:
- Superior canal dehiscence,
- Meniere's syndrome,
- other causes of perilymph fistula,
- post fenestration surgery(for otosclerosis).