How to distinguish between SCC Dehiscence and Perilymphatic Fistula On Clinical Basis/History?
Superior semicircular canal dehiscence (SSCD) and perilymphatic fistula (PLF) are both conditions involving leakage of perilymphatic fluid from the inner ear, but they have distinct underlying causes and clinical presentations. Here’s how they can be distinguished based on clinical history:
- Superior Semicircular Canal Dehiscence (SSCD):
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Clinical History:
- Patients with SSCD often report experiencing a range of auditory and vestibular symptoms, including autophony (hearing one’s own voice or bodily sounds), pulsatile tinnitus (hearing rhythmic pulsing noises in the ear), sound-induced vertigo or dizziness (Tullio phenomenon), and/or vertigo or dizziness triggered by changes in middle ear or intracranial pressure (Hennebert sign).
- Symptoms may be exacerbated by loud noises, changes in atmospheric pressure (e.g., flying, scuba diving), or maneuvers that increase intracranial pressure (e.g., coughing, straining).
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Associated Factors:
- SSCD is often associated with thinning or absence of the bone overlying the superior semicircular canal, leading to a “third window” effect that disrupts normal vestibular and auditory function.
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Diagnosis:
- Diagnosis of SSCD is typically confirmed through high-resolution temporal bone CT imaging, which can reveal thinning or absence of bone overlying the superior semicircular canal.
- Perilymphatic Fistula (PLF):
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Clinical History:
- Patients with PLF may present with a history of sudden onset of vertigo or dizziness following a head injury, barotrauma (e.g., scuba diving, air travel), or straining (e.g., heavy lifting, coughing).
- Symptoms may also include fluctuating hearing loss, tinnitus, aural fullness, and imbalance.
- Patients may report that symptoms worsen with changes in atmospheric pressure, such as flying or descending in an elevator.
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Associated Factors:
- PLF involves a tear or rupture in the membranes that separate the inner ear from the middle ear or surrounding structures, allowing perilymphatic fluid to leak into the middle ear space.
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Diagnosis:
- Diagnosis of PLF can be challenging and is often based on clinical history, physical examination findings, and sometimes confirmed through diagnostic tests such as tympanometry, vestibular function testing, or exploratory tympanotomy.
In summary, distinguishing between SSCD and PLF based on clinical history involves assessing the nature of symptoms, triggers, and associated factors. While both conditions may involve auditory and vestibular symptoms, SSCD is often characterized by symptoms related to sound and pressure changes, while PLF may be associated with symptoms following trauma or changes in atmospheric pressure. Imaging studies and further diagnostic testing may be necessary to confirm the diagnosis.