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Vestibular Aqueduct Dehiscence

Summary

  • A "third window" lesion in which the bone separating the vestibular aqueduct from an adjacent high-riding jugular bulb is deficient
  • Presents with pulsatile tinnitus and pressure- or sound-induced vertigo
  • Diagnosed on high-resolution temporal bone CT1

Pathophysiology

  • Dehiscence creates an abnormal "third window" into the labyrinth, dissipating acoustic/pressure energy and abnormally stimulating the vestibular system
  • Typically occurs where a high-riding or diverticular jugular bulb erodes the vestibular aqueduct

Diagnosis

  • Pulsatile tinnitus, sound- or pressure-induced (Tullio) vertigo, sometimes a low-frequency air–bone gap
  • Clinically overlaps with other third-window lesions such as superior semicircular canal dehiscence

Imaging

  • High-resolution temporal bone CT is the key test:
    • Focal bony defect between the vestibular aqueduct and the jugular bulb
    • Usually an associated high-riding or dehiscent jugular bulb
  • Reformatting along the plane of the aqueduct avoids overcalling dehiscence from partial-volume averaging

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  • A 40-year-old patient presented with constant right sided pulsatile tinnitus and intermittent vertigo.
  • CT showed a communication/dehisence of the right vestibular aqueduct (red arrows) onto a high-riding jugular bulb.

Treatment

  • Usually conservative; surgical resurfacing is reserved for disabling symptoms once other causes are excluded

Differential diagnosis

Imaging differential Differentiating feature
Superior semicircular canal dehiscence Bony defect over the superior semicircular canal rather than the vestibular aqueduct
Sigmoid sinus dehiscence Absent bone over the sigmoid plate — a venous cause of pulsatile tinnitus
Enlarged vestibular aqueduct Widened aqueduct (>1.5 mm) causing sensorineural hearing loss, without a jugular bulb defect
Glomus tympanicum / jugulare Enhancing vascular middle-ear or jugular foramen mass

  1. Guarnizo et al. High jugular bulb with a diverticulum and vestibular aqueduct dehiscence: an anatomical variant to be aware in patients with hearing loss. 2022. Surgical and radiologic anatomy : SRA - Open in new tab. ↩