Inner anterior canal fistula. A new variant of perilymphatic fistula

In 1998 Minor et al. described a new variant of perilymphatic fistula: the "superior canal dehiscence syndrome". This syndrome is clinically character ized by recurrent attacks of vertigo and oscillopsia induced by loud noises or stimuli that result in changes in intracranial or middle ear pressure. It is caused by a dehiscence of bone overlying the superior (anterior) semi circular canal. Due to this dehiscence, a third, mobile window (in addition to the round and oval windows) is formed, and changes in pressure are path ologically transduced to the anterior semicircular canal. Although the supe rior canal dehiscence syndrome is not a rare condition, no other cases have yet been reported. Therefore, we describe a typical patient who suffered f or many years from recurrent attacks of vertigo and oscillopsia induced by coughing and Valsalva's maneuvers. High resolution temporal bone CT scan sh owed a defect in the bone overlying the left anterior semicircular canal. T hree-dimensional eye movement recordings using the search coil technique an d subsequent vector analysis demonstrated that the eye movements were induc ed by excitation of the left anterior semicircular canal. We conclude that superior canal dehiscence syndrome is an important differential diagnosis i n patients suffering from symptoms of a perilymphatic fistula, especially s ince it can be successfully treated by "plugging" of the affected semicircu lar canal. Such patients are thus spared unnecessary surgery of the middle ear.