Normal Vestibular Aqueduct Canal Size: CT Reference
The vestibular aqueduct is a bony canal within the petrous temporal bone that houses the endolymphatic duct, connecting the membranous labyrinth to the endolymphatic sac. Accurate measurement of its diameter on CT is essential for evaluating sensorineural hearing loss and suspected inner ear malformations.
Normal Reference Values
| Measurement |
|---|
| <1.5 mm |
Clinical Significance
A vestibular aqueduct diameter of 1.5 mm or greater is considered enlarged and is the key imaging criterion for Large Vestibular Aqueduct Syndrome (LVAS), one of the most common identifiable causes of congenital and progressive sensorineural hearing loss in children. Enlargement reflects dysplastic development of the endolymphatic duct and sac, leading to abnormal endolymph homeostasis.
Pendred syndrome — an autosomal recessive condition caused by SLC26A4 mutations combining sensorineural hearing loss with thyroid goiter — is a classic association with enlarged vestibular aqueducts. However, enlargement may also occur in isolation (non-syndromic LVAS) or alongside other inner ear anomalies such as incomplete partition type II (Mondini malformation). Patients are at risk of sudden hearing deterioration following minor head trauma, warranting protective counseling.
- Large Vestibular Aqueduct Syndrome (isolated)
- Pendred syndrome (SLC26A4 mutations)
- Mondini malformation / incomplete partition type II
- CHARGE syndrome (associated inner ear anomalies)
- Branchio-oto-renal syndrome
Reference: Goldfeld M, Glaser B, Nassir E et al. CT of the ear in Pendred syndrome. Radiology. 2005;235(2):537-40.
Imaging Notes
High-resolution CT (HRCT) of the temporal bones is the primary modality for evaluating the vestibular aqueduct. Thin-section axial images (0.5–1 mm slice thickness) with bone-algorithm reconstruction are required. The canal is best measured at its midpoint in the axial plane, perpendicular to its long axis, at the isthmus — the narrowest portion midway between the common crus and the operculum. Care should be taken to distinguish the bony canal from the adjacent endolymphatic sac, which extends beyond the temporal bone and may appear larger on MRI. Symmetric evaluation of both sides is recommended, as bilateral enlargement supports a hereditary etiology.