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17	"Spectrum of ear deformities that..." Spectrum of ear deformities that involve abnormal development of the 1^st and 2^nd branchial arches and the 1^st branchial groove. External ear, tympanic membrane, ossicles, and middle ear may be affected; the majority have normal inner ear development. The Jahrsdoerfer classification uses a score (up to 10) based upon findings on CT scans to grade severity of atresia by assigning 1 point for an open oval window, width of the middle ear cleft, facial nerve course, malleus-incus complex, mastoid pneumatization, incudo-stapedial continuity, round window patency, and auricle appearance and 2 points for the presence of the stapes. Presence of the stapes is an important predictor for good surgical outcome and is therefore given more weight when using the Jahrsdoerfer classification. As an absent oval window is almost always associated with absence of the stapes, it is important to identify this finding. As illustrated in the cases in our exhibit, the stapes was not seen in the setting of an atretic oval window. Additionally, patients with absent stapes and oval window will often have an anomalous course of the facial nerve. 2D CT provides source data, which when reformatted to 3D CT allows the user to rotate or dissect the image in any plane, providing both supplementary information and an interface more recognizable for the clinician.
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24	"The bony superior semicircular canal..." The bony superior semicircular canal is the first to fully develop at 21 weeks gestation, with the posterior forming by 22 weeks, and lastly the lateral at 23 weeks gestation. Malformation of the superior and posterior semicircular canals without involvement of the lateral canal is therefore unusual, as the lateral semicircular canal is the last to develop. As the cases in our exhibit demonstrate, it can be difficult to ascertain the absence of the common crus based on the 2D images. The 3D reformations easily demonstrate the absent common crus helping us establish a better embryologic correlate with respect to dysplastic semicircular canals.
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