RSS Channels IndexRare Orientation of the Internal Auditory Canal Found in Eight Year Old
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Source: American Society of Pediatric Otolaryngology (ASPO)
Newswise — Radiological abnormalities of the inner ear are seen in only 20 percent of patients with congenital hearing loss. Specifically, abnormalities of the internal auditory canal (IAC) [the bony inner portion of the passage leading inward through the tympanic portion of the temporal bone, from the auricle to the tympanic membrane], are relatively uncommon. In those 20 percent of patients with hearing loss and radiological findings, only 12 percent will demonstrate narrowed IACs and nine percent wide IACs. These variations from normal are usually seen in association with other inner ear malformations. These can include internal auditory canals that are exposed, oval in cross-section as opposed to the normal round shape, and those that taper down the center.
However, there are no reports that describe IAC variations in its orientation as it courses through the bony interior and possible association with hearing loss. Researchers have discovered such a case and make a report in the poster study "Vertically Oriented Internal Auditory Canal in an 8 year old with Hearing Loss." The authors are Gregory J. Artz MD, and Vijay M. Rao MD, from the Thomas Jefferson University Hospital, Philadelphia, PA; and Robert C. O'Reilly MD and Jay D. Luft MD, both from the A.I duPont Children's Hospital, Wilmington, DE. Their findings are being presented at a combined session of the American Society of Pediatric Otolaryngology and the Triological Society, being held April 30 - May 3, 2004, at the JW Marriott Desert Ridge Resort & Spa, Phoenix, AZ.
Case Report: An eight-year-old Hispanic boy with a long-standing history of otitis media presented to A.I duPont Children's Hospital in September 2003 for further evaluation of a mixed hearing loss and an abnormal CT scan of the temporal bone. Between January 2000 and November 2002 he had placement of tympanostomy tubes on three separate occasions for failure of medical therapy and a persistent mild-moderate mixed hearing loss.
The patient's birth history and developmental histories were unremarkable. His medical history was significant for several uncomplicated hospitalizations for upper respiratory infections. The physical examination was unremarkable. Tympanostomy tubes were in place and open. An audiometry revealed a mild to moderate mixed hearing loss with an average air-bone gap of 20 Db. Speech reception threshold (SRT) readings were 25 Db in both ears with a 96 percent word recognition score.
A CT scan of the temporal bone was performed in June 2003. An axial image revealed the vertical orientation of the internal auditory canal with normal orientation and morphology of the bony labyrinth, but with a parallel orientation to the sagittal plane. A coronal image confirmed the vertical orientation of the IAC in relation to the horizontal plane. This image also displays the normal anatomical orientation of the external auditory canal and middle ear space. Treatment for this patient included close follow-up in clinic with repeat physical exam and audiometric evaluation.
Conclusions: In most healthy individuals the internal auditory canal travels horizontally, terminating at the vestibule. The average vertical diameter is four mm with variations of normal ranging from 2-8 mm. Anatomical variations of the internal auditory canal are usually described as narrow, wide, and open. There is no discussion of abnormal orientation of the IAC in relation to its horizontal course from the porus acusticus to its end point at the vestibule.
To our knowledge there are no reports in the literature of vertically oriented IAC. In this report there is no way to prove or disprove the relationship between this finding and the patient's hearing loss. A large study of temporal bone anatomy is needed to determine an incidence of this rare finding and to determine the association, if any, with hearing loss.
Although a vertical internal auditory canal is not a common condition, the finding of this case study should be an alert to radiologists and otolaryngologist that variation in the temporal bone may help explain patient pathology, such as hearing loss.
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