Relationship between multidetector CT imaging of the vestibular aqueduct and inner ear pathologies

Abstract

This study investigated the relationships between morphological changes in the vestibular aqueduct (VA) in different inner ear pathologies. Eighty-eight patients (34 males and 54 females, ranging from seven to 88 years of age; average age 49.2 years) with cochleovestibular disorders underwent temporal bone CT (with a 64-channel helical CT system according to temporal bone protocol parameters; 0.6 mm slice thickness, 0.6 mm collimation, bone reconstruction algorithm). All patients with cochleovestibular disorders who underwent temporal bone CT had been previously divided into six different suspected clinical classes: A) suspected pathology of the third window; B) suspected retrocochlear hearing loss; C) defined Ménière's disease; D) labyrinth lithiasis; E) recurrent vertigo. On CT images we analyzed the length, width and morphology of the VA, contact between the VA and the jugular bulb (JB), the thickness of the osseous capsule covering the semicircular canals, the pneumatization rate of the temporal bone and the diameter of the internal auditory canal. At the end of the diagnostic work-up all patients were grouped into six pathological classes, represented as follow: 1) benign paroxysmal positional vertigo (BPPV), 2) recurrent vertigo (RV), 3) enlarged vestibular aqueduct syndrome (EVAS), 4) sudden or progressive unilateral sensorineural hearing loss (SNHL), 5) superior semicircular canal dehiscence syndrome (SSCD), 6) recurrent vestibulocochlear symptoms in Ménière's disease. We evaluated 176 temporal bones in 88 patients. The VA was clearly visualized in 166/176 temporal bones; in ten ears the VA was not visualized. In 14 ears (11 patients, in three of whom bilaterally) we found an enlarged VA while in 31 ears the VA was significantly narrower. In 16 ears a dehiscence of the JB with the vestibular or cochlear aqueduct was noted. In all six patients with suspected EVAS we found a AV wider than 1.5 mm on CT scans; moreover CT identified four patients with large VA and ill-defined clinical symptoms. Most patients with BPPV (11 patients, Class 1) we did not find any VA abnormalities on CT scans, confirming the clinical diagnosis in ten patients; in the remaining patients we found an enlarged VA, not clinically suspected. In the RV class (eight patients, Class 2) we found three patients with negative CT scans, two patients with narrow aqueduct and subsequently reclassified as Ménière's disease patients, and three patients with ectasic JB dehiscence with the VA. In patients suffering from SNHL we found no statistically significant correlation with the morphological abnormalities. The clinical suspicion of SSCD was confirmed by CT in 11/13 patients (84.6 %); in addition another seven patients showed a thinning or dehiscence of the superior semicircular canals as the prevailing alteration on CT scans, and were reclassified in this group. Ménière's disease symptoms were correlated with a VA alteration in more than half of the cases; the most striking finding in this class was that the VA was significantly narrower (21 patients). Our study demonstrates that alterations of the VA morphology are not only related to EVAS but are also found in other inner ear pathologies such as Ménière's disease. Furthermore, MDCT may confirm the presence of correlations between the morphology of inner ear structures such as VA, semicircular canals or JB dehiscence, and alterations of vestibulocochlear function.

Keywords: bony labyrinth; cochleovestibular diseases; multidetector computed tomography; temporal bone; vestibular aqueduct.

Figure 1

Axial orbitomeatal CT images with measurements of the vestibular aqueduct: A) VA width measured at the midpoint between the external aperture and common crus; B) external aperture width; C) VA length.

Figure 2

MPR CT images reformatted on Pöschl's plane with measurements of the vestibular aqueduct. A) VA width measured at the midpoint between external aperture and common crus; B) external aperture width; C) VA length.

Figure 3

Axial orbitomeatal CT images with morphological qualitatively evaluation of the vestibular aqueduct. A) Not visualized, B) visualized with difficulty / narrow, C) normal, D) borderline and E) enlarged.

Figure 4

Axial and coronal CT images. A) Dehiscence of the jugular bulb with the vestibular aqueduct. B) 45-year-old female with recurrent dizziness not responding to drug therapy. CT images show enlarged JB dehiscent with both cochlear and vestibular aqueducts. C) Distance between jugular bulb and posterior semicircular canal bony wall.

Figure 5

Coronal CT images and min-IP images reconstructed on semicircular canals with thickness evaluation. A, B) Normal condition. C, D) Thinning (arrow in C) of the osseous capsule covering the superior semicircular canal. E, F) Dehiscence (arrow in E) of the osseous capsule covering the superior semicircular canal.

Figure 6

Axial and coronal CT images: length of the internal auditory canal (A) and diameter of the internal acoustic meatus (B).