What syndromes can cause bilateral semicircular canal dehiscence (SCD)?

Syndromes Causing Bilateral Semicircular Canal Dehiscence

Ehlers-Danlos syndrome, particularly the hypermobility type (EDS-HT), is the primary syndrome associated with bilateral superior semicircular canal dehiscence (SSCD), with multiple case reports documenting this association. 1, 2

Primary Syndrome Association

Ehlers-Danlos Syndrome (EDS-HT)

• EDS-HT is a genetic collagen synthesis disorder that results in bony abnormalities and bone fragility, predisposing patients to develop bilateral SSCD. 1, 2
• The defective collagen synthesis in EDS creates temporal bone thinning and structural weakness, making the superior semicircular canal vulnerable to dehiscence formation. 1, 2
• Multiple case reports have documented bilateral SSCD occurring specifically in patients with confirmed EDS-HT, with patients presenting with characteristic auditory and vestibular symptoms including autophony, sound-induced vertigo (Tullio phenomenon), and conductive hearing loss. 1, 2
• Patients with EDS-HT who undergo surgical repair via middle fossa craniotomy report symptomatic improvement, confirming the clinical significance of this association. 1, 2

Clinical Presentation in Syndromic Cases

Characteristic Symptoms to Identify

• Autophony, inner ear conductive hearing loss, Hennebert sign (vertigo induced by pressure changes), and sound-induced episodic vertigo (Tullio phenomenon) are the hallmark symptoms of SSCD. 3
• Patients may present with bilateral auditory and vestibular symptoms when both superior semicircular canals are affected. 2
• The syndrome differs from benign paroxysmal positional vertigo (BPPV) because vertigo is induced by pressure changes (Valsalva maneuvers) rather than positional changes. 4

Diagnostic Approach for Syndromic SSCD

Imaging Confirmation

• High-resolution computed tomography (CT) of the temporal bones with fine-cut (0.5- to 0.6-mm) collimation reformatted parallel and orthogonal to the plane of the superior canal is the gold standard for confirming bilateral SSCD. 3, 1
• CT imaging reveals the bony dehiscence creating an opening between the inner ear and middle cranial fossa bilaterally. 1

Functional Testing

• Vestibular evoked myogenic potentials (VEMPs) and specific auditory testing prove useful in detecting and evaluating dehiscence syndrome. 3
• Valsalva maneuvers during clinical examination can provoke symptoms and aid in diagnosis. 3

Other Potential Etiologies (Non-Syndromic)

While the question specifically asks about syndromes, it's important to note that bilateral SSCD can also occur with:

• Congenital developmental abnormalities associated with multiple temporal bone malformations, though these typically occur without other craniofacial or systemic syndromes. 5
• Temporal bone fractures from closed head trauma can cause SSCD, though bilateral traumatic cases would be exceedingly rare. 6

Clinical Screening Recommendations

For patients with known EDS-HT, perform auditory and vestibular evaluation with assessment for bony abnormalities of the temporal bone, as this population has increased predisposition to bilateral SSCD. 2