What is Fistula test?
Fistula test is a test done to detect a fistula in the bony labyrinthine wall of the inner ear.
What is the basis (principle) on which Fistula test works?
Principle: Pressure changes in the external auditory canal are transmitted to the labyrinth via the fistula which produces nystagmus.
How is Fistula test done?
In Fistula test, pressure changes in the external canal are brought by applying intermittent pressure on the tragus or by Siegel's speculum. In a normal person, the test is negative because the pressure changes cannot be transmitted into the labyrinth (when there is no fistula).
How are the results of Fistula test interpreted?
1. In fistula over the dome of the lateral semicircular canal: Increase pressure causes conjugate horizontal deviation of the eyes towards the normal side. As pressure is maintained, jerk nystagmus develops with fast component towards the affected ear. As pressure is released, eyes return to normal
2. Fistula of the lateral semicircular canal (anterior to the ampulla) causes deviation of eyes, to the affected side
3. Vestibular erosion causes rotatory horizontal nystagmus towards the diseased ear
4. Fistula of the posterior semicircular canal causes vertical movement of eyes.
In which other cases is the Fistula Test positive?
Apart from the above, the Fistula test is positive in:
a. Fenestration surgery (Post-stapedectomy)
b. Round window rupture
Which conditions can give rise to false-positive Fistula test?
False-positive fistula test may be seen in following cases in spite of the absence of fistula:
1. Congenital syphilis
2. Meniere's disease – (Hennebert's sign)
3. Hypermobile stapes footplate
Which conditions can give rise to false-negative Fistula test?
False-negative fistula test may be seen in following cases in spite of the presence of fistula:
1. Cholesteatoma covering the fistula
2. Dead labyrinth.