Third window effect is seen in:

Ans. b. Dehiscent superior semicircular canal (Ref: www.utmb.edu/otoref/gmds/third%20window-061108/third-window-slides-061108.pdf)Third window effect is seen in dehiscent superior semicircular Canal.Absence of the bone overlying the superior semicircular canal resulting in a third window to the membranous labyrinth that may result in a syndrome of vestibular and auditory symptomsQ.Superior Canal DehiscenceAbsence of the bone overlying the superior semicircular canal resulting in a third window to the membranous labyrinth that may result in a syndrome of vestibular and auditory symptomsQ.Syndrome was first described by Minor in 1988.Sound or pressure induced vertigo due to bone dehiscence of the superior semicircular canalQ (Arch of Otolaryngology, Head and Neck Surgery)Third Window Hypothesis:In superior semicircular canal dehiscence, it is hypothesized that some fractions of the perilymphatic volume displaced by the oscillating stapes is shunted through the superior canal away from the cochlea, resulting in a decrease in the sound conducted to cochlea.Dehiscence of Superior Semicircular Canal Results inSound and pressure induced vestibular symptomsIncreased sensitivity of bone conducted soundDecreased sensitivity of air conducted sound