Three-dimensional computed tomography of superior canal dehiscence syndrome.
OBJECTIVE
To compare 3-dimensional (3-D) surface reconstructions of the temporal bone with presently used multiplanar reconstructions (MPRs) from high-resolution computed tomographic (HRCT) data sets in patients with superior canal dehisence syndrome (SCDS). Results of audiometry, vestibular evoked myopotentials (VEMPs), and clinical testing are also considered.


METHODS
: Twenty-one adults with unilateral or bilateral SCD.


METHODS
High-resolution computed tomographic scans, audiograms, VEMP testing.


METHODS
Comparison of findings on 3-D surface reconstructions with MPRs; predictive values of different tests.


RESULTS
High-resolution computed tomographic scans were performed on 6 subjects with bilateral SCD and 15 with unilateral SCD. High-resolution computed tomographic scans were examined as MPRs in the plane of the SC and in perpendicular radial cuts through the SC. High-resolution computed tomographic scans were also analyzed as 3-D surface reconstructions. Compared with the MPRs, 3-D surface reconstructions for patients who had at least 1 objective finding suggestive of SCDS had a 68% positive predictive value, 91% sensitivity, and 47% specificity. None of those temporal bones that had intact SCs on MPRs had other objective findings suggestive of SCDS. Three-dimensional surface reconstructions often made SCs covered with thin bone seem dehiscent, exposed air cells can be mistaken for SCDS, and a large dehiscence can sometimes be missed. Nystagmus evoked by 110-dB relative-to-normal-hearing-level tones was 100% specific for SCDS when present but only 67% sensitive. Decreased click evoked VEMP threshold was 80% sensitive and 80% specific for SCDS. Conductive hearing loss of 10 dB or greater had an 83% sensitivity and 95% specificity.


CONCLUSIONS
Multiplanar reconstructions of HRCT data are the most sensitive test for diagnosis of SCD. False SCD and missed SCD can occur with 3-D surface reconstructions of the temporal bone. Determination of SCD should be based on MPRs of an HRCT data instead of 3-D surface reconstructions, but the latter remain valuable for surgical planning. The decision for surgery in SCDS should not be based on imaging results alone but also on the physiologic findings and the frequency and severity of symptoms.
Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Johns Hopkins Outpatient Center, Baltimore, Maryland 21287-0910, USA.
Benjamin T
BT
Crane
Lloyd B
LB
Minor
John P
JP
Carey
D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012665:Semicircular Canals / Q000000981:diagnostic imaging*; D013529:Surgical Wound Dehiscence / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed; D014722:Vestibule, Labyrinth / Q000502:physiology