Tullio's phenomenon is caused by a thinning or absence (dehiscence) of the bone covering one or more of the semicircular canals in the inner ear.
Understanding Tullio's Phenomenon
Tullio's phenomenon (TP) is a clinical symptom where certain sounds or movements trigger dizziness, vertigo, and/or nystagmus (involuntary eye movements). This abnormal response occurs because the inner ear's balance system (vestibular system) is abnormally sensitive to these stimuli.
The Underlying Cause: Bone Defects
The most common cause of Tullio's phenomenon is a defect in the bone surrounding the semicircular canals. Specifically:
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Superior Canal Dehiscence (SCD): This is the most well-known cause. SCD occurs when there's a thinning or complete absence of bone overlying the superior semicircular canal. This creates an abnormal "third window" in the inner ear, making it sensitive to pressure changes from sound or movements.
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Other Canal Dehiscences: While less common, similar dehiscences in the posterior or lateral semicircular canals can also lead to Tullio's phenomenon.
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Thinning of the Bone: In some cases, the bone may not be completely absent (dehiscence) but is significantly thinned, making the inner ear structures more vulnerable to external stimuli.
How Bone Defects Cause Tullio's Phenomenon
Normally, the bony labyrinth protects the delicate inner ear structures. When a dehiscence or thinning occurs:
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Sound or Pressure Sensitivity: Sounds (especially loud ones) or pressure changes from movements can directly stimulate the semicircular canals.
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Abnormal Fluid Movement: This stimulation leads to abnormal fluid movement within the affected semicircular canal.
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Incorrect Signals: The brain misinterprets these abnormal signals as movement, leading to the symptoms of dizziness, vertigo, and nystagmus.
Other Potential Causes (Less Common)
While bone defects are the primary cause, other conditions, although rare, can contribute to Tullio's phenomenon:
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Perilymph Fistula: A leak of the inner ear fluid (perilymph) can create pressure imbalances that trigger symptoms.
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Meniere's Disease: Although less directly related, Meniere's disease can, in some cases, present with symptoms resembling Tullio's.
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Post-Stapedectomy: Rarely, after stapedectomy surgery (a procedure to improve hearing), some patients develop Tullio's phenomenon.
In summary, Tullio's phenomenon is most commonly caused by a thinning or dehiscence in the bone surrounding the semicircular canals, most notably Superior Canal Dehiscence (SCD), which allows abnormal stimulation of the inner ear's balance system by sound or pressure changes.
