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superior semicircular canal dehiscence syndrome ( scds ) is a recently recognized clinical condition , which was initially described by minor , et al.1 ) the syndrome usually encompasses a constellation of vestibular and audiological symptoms , such as sound and/or pressure induced vertigo and oscillopsia , along with conductive hearing loss and autophony , and typically manifests as sound and/or pressure induced nystagmus at the plane of the superior semicircular canal ( ssc).2 - 4 ) the proposed underlying mechanism involves the existence of a dehiscence at the apex of the ssc ( third mobile window ) , in addition to the round and oval windows of the osseous cochlea , which in effect potentiates the transmission of sudden changes in the middle and/or intracranial pressure , thus altering the related neural firing rates of the vestibular system , and may also alter inner ear fluid dynamics , causing dissemination of the acoustic energy.5,6 ) while the classic presentation can be suspected on clinical and audiometric data , imaging plays an important role in the evaluation of these patients . advances in computed tomography ( ct ) now allow high resolution images to demonstrate the bony defect , while multiplanar reformations can also aid in the radiologic diagnosis.7 - 9 ) despite the several investigations on this condition , there are no clear causes of scds . certainly , a congenital / developmental basis for the condition has been described.9 - 13 ) there was a report describing the development of scds from an intact ear , confirmed by serial follow - up ct scans.14 ) in that study , osteomyelitis and increased bony absorption associated with chronic brain pulsation might be one of the possible causes of scds .
because inflammatory process is related to the decreased mastoid air - cell volume,15,16 ) we wanted to compare the mastoid air - cell volume of the patients with scds and that of the age- and sex - matched patients with otosclerosis and temporal bone ( tb ) fracture , who are supposed to represent normal mastoid pneumatization .
10 patients with scds confirmed by symptoms , signs , vestibular evoked myogenic potential and tb ct imaging were enrolled . to compare the mastoid air - cell volume ,
the otosclerosis and tb fracture patients identified in the tb ct were selected as control groups .
the otosclerosis was identified in both sides , and with no other pathology , such as chronic otitis media ( com ) and middle ear effusion .
this study was approved by the institutional review board of our institute and followed the recommended guidelines .
high - resolution tb ct scans were performed using a 64 row detector ct scanner ( siemens , medical system , erlanger , germany ) .
the axial plane images were acquired using a 0.6 mm section thickness at 200 ma and 120.0 kv .
the coronal and oblique sagittal reconstruction images , which were parallel to the superior semicircular canal , were acquired using 0.4 mm interval reconstructions .
all of the images were evaluated on a diagnostic petavision pacs station ( emsoma , seoul , korea ) . to measure the mastoid air - cell volume , we used 3d reconstruction software .
the imaging data were stored in a digital imaging and communication in medicine file and then imported to a personal computer running vworks 4.0 software ( cybermed , seoul , korea ) . when performing reconstruction using a surface rendering algorithm , the selection of the window thresholds were -1024 to -318 hounsfield units .
the volume of mastoid air - cell was automatically calculated in the 3d reconstruction ( fig .
statistical analysis was conducted using wilcoxon signed rank test to compare volume between the scds side and the normal side in scds patients , and left and right side of the otosclerosis patients .
the differences of mastoid air - cell volume in the scds , otosclerosis and tb fracture were determined using the kruskal - wallis test and mann - whitney u test .
all statistical analyses were performed using spss 20.0 software ( spss , ibm corp . , armonk , ny , usa ) , and the p values < 0.05 were considered significant .
mean mastoid air - cell volume in scds side was 3319.9 mm , whereas 4177.2 mm in the normal side ( table 1 ) .
there was a significant difference of the mastoid air - cell volume between the lesion side and the normal side of scds patients ( p=0.022 , wilcoxon signed rank test ) .
mean mastoid air - cell volume of otosclerosis patients was 6594.3 mm in the right side and 6380.5 mm in the left side ( table 1 ) .
and there was no significant difference of mastoid air - cell volume between the right and left sides ( p=0.445 , wilcoxon signed rank test ) .
mean mastoid air - cell volume in normal side of tb fracture was 6477.2 mm ( table 1 ) .
there is no difference between the mastoid air - cell volume of the otosclerosis and that of tb fracture patients ( p=0.684 ) .
the mastoid air - cell volume of the scds ( both sides ) showed significant difference compared to that in any side of the otosclerosis patients ( p=0.013 , kruskal - wallis test ) . in the post - hoc analysis ,
the mastoid air - cell volume in scds side was significantly smaller than those of otosclerosis patients ( p=0.009 , mann - whitney u test)(fig .
2 ) . however , the difference between the mastoid air - cell volume in the normal side of scds patients and that of otosclerosis patients was not significant ( p=0.063 , mann - whitney u test ) .
similarly , the mastoid air - cell volume of the scds ( both sides ) showed significant difference compared to that in tb fracture patients ( p=0.006 , kruskal - wallis test ) . in the post - hoc analysis ,
the mastoid air - cell volume in scds side and normal side of scds patients were significantly smaller than that of tb fracture patients ( p=0.002 , p=0.019 , respectively , mann - whitney u test)(fig .
the decrease of mastoid air - cell volume could be seen several conditions , such as otitis media with effusion , com , and cholesteatoma.15,16 ) many studies reported that the inflammatory process is related to the decreased mastoid air - cell volume .
our results demonstrated significantly smaller mastoid air - cell volume in the scds side than in that of the otosclerosis patients and tb fracture patients ( p=0.009 , p=0.002 , respectively ) . the mastoid air - cell volume ( 4177.2 mm ) in the normal side of scds patients was smaller than that ( 6594.3 mm in the right ear and 6380.5 mm in the left ear ) of the otosclerosis patients , although it was not significant ( p=0.063 ) .
but , the mastoid air - cell volume in the normal side of scds patients significantly smaller than tb fracture patients ( 4177.2 mm vs. 6477.2 mm , p=0.019 ) . because no patients with scds in this study had soft tissue density in the mastoid in tb ct scans , suggesting there is no active inflammation in the mastoid , inflammatory process ( acute otitis media or middle ear effusion ) in the early childhood could have had a role in the decreased mastoid air - cell volume in the scds ear .
it remains unclear whether scds is a congenital / developmental disorder or whether it is acquired .
it has been reported that tb specimens from infants show uniformly thin bone over the superior canal in the middle fossa at birth , with gradual thickening until 3 years of age , and that scds may arise from failure of postnatal bone development.9 ) tsunoda and terasaki17 ) has described the embryological basis for dehiscence .
if the otocyst is situated close to the developing brain during this stage , there is inadequate space for the growth of the superior surface of the superior semicircular canal as the otocyst may lie against the dura . hindering gradual thickening of the superior canal roof by otitis media before the age of 3 , associated with the decreased mastoid pneumatization ,
additionally , scds may be generated by chronic brain pulsation and the pressure exerted by the temporal lobe on the middle cranial fossa.9 ) however , another study demonstrated that the radiologic prevalence of scds among older age groups increases , suggesting that scds is more commonly an acquired rather than developmental condition.18 ) chronic bone inflammation by previous otitis media in childhood , which can be identified as having decreased mastoid volume , may render the bone overlying the superior canal susceptible to brain pulsation or the pressure from the temporal lobe , resulting in the generation of scds .
our findings revealed that the mastoid air - cell volume in the scds side was significantly smaller than that of otosclerosis and tb fracture patients , furthermore the volume in the normal side of scds patients was significantly smaller than that of tb fracture patients , which suggest that the decreased mastoid pneumatization is closely related to the generation of scds , whether scds is a congenital / developmental disorder or whether it is acquired .
background and objectivesthe purpose of the study was to compare the mastoid air - cell volume of the patients with superior semicircular canal dehiscence syndrome ( scds ) and that of the control patients with otosclerosis and temporal bone ( tb ) fracture.subjects and methodsten patients with scds were enrolled and 10 patients with bilateral otosclerosis and tb fracture were selected as control groups by age and sex matching . to measure the mastoid air - cell volume , 3d reconstruction software was used.resultsin 10 patients with scds , the mean age was 44.5 years , ranging from 16 to 79 years ( m : f=4 : 6 ) . 
 mean mastoid air - cell volume in the scds side was 3319.9 mm3 , whereas 4177.2 mm3 in the normal side ( p=0.022 ) . 
 mean mastoid air - cell volume in the right side of otosclerosis patients was 6594.3 mm3 and it was not different from 6380.5 mm3 in the left side ( p=0.445 ) . 
 mean mastoid air - cell volume in normal side of tb fracture was 6477.2 mm3 . 
 the mastoid air - cell volume in the scds side was significantly smaller than that of otosclerosis and tb fracture patients ( p=0.009 , p=0.002 , respectively ) . 
 the mastoid air - cell volume in the normal side of scds was significantly smaller than that of tb fracture ( p=0.019 ) , but not significant with that of otosclerosis ( p=0.063).conclusionsour findings revealed that the mastoid air - cell volume in the scds side was significantly smaller than control group , which suggest that the decreased mastoid pneumatization is closely related to the generation of scds .