Marie Christianne Hoeberigs MD, Abstract Co-Author: Nothing to Disclose

Alida Annechien Postma MD, PhD, Presenter: Nothing to Disclose

Jerome J. Waterval, Abstract Co-Author: Nothing to Disclose

R. J. Stokroos, Abstract Co-Author: Nothing to Disclose

Annika A.R Stadler, Abstract Co-Author: Nothing to Disclose

In patients with otosclerosis an otosclerotic hypodens cavitating plaque at the medial margin of the otic capsule, seen as an indentation or "diverticulum" of the anterior margin of the internal auditory canal (IAC), might be present. We aimed to determine the prevalence of this easily identifiable anterior IAC indentation on CT in patients with otosclerosis.  

222 consecutive high resolution CT scans (0.4-0.6 mm) of the mastoid bone in patients with conductive or mixed hearing loss from January 2008 to December 2010 were retrospectively reviewed by 2 neuroradiologists and 1 ENT surgeon. A total of 444 ears was scored for presence and severity of otosclerosis (graded according to the Symons/Fanning classification: 1 fenestral; 2 patchy pericochlear; 3 extensive pericochlear) and for the presence of anterior IAC diverticulum/plaque. This was defined as an obvious notch in the anterior IAC margine, isodense to the IAC itself; a faint curvature of the wall was scored negative.  

Anterior IAC diverticulum was observed in 9/92 ears (10%) with only fenestral otosclerosis; in 9/35 (25%) of grade 2 patchy cochlear otosclerosis and in 14/20 (70%) with grade 3 otosclerosis. Only 1 patient without CT-signs of otosclerosis, but with clinical stapedial fixation (thus, clinically suggestive of otosclerosis) demonstrated bilateral IAC hypodensity (2/297 ears or 0.6%).  

Prevalence of an IAC identation is related to the severity of otosclerosis.  

When looking for otosclerosis on HR CT, IAC margins should be carefully evaluated.

Hoeberigs, M, Postma, A, Waterval, J, Stokroos, R, Stadler, A, Prevalence of Anterior Internal Auditory Canal "Diverticulum" on High Resolution CT in Patients with Otosclerosis.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12029990.html