Appropriate patient selection is critical to the arguments supporting unilateral atresia surgery. It is obviously important as well for surgical intervention in bilateral cases, although the criteria are less strict in this latter circumstance.
Most patients undergoing atresia repair will have a residual conductive deficit of > 10 dB. Sensorineural function should, therefore, be normal in order to maximize the potential for achieving binaural hearing. Normal or near-normal sen-sorineural function in the contralateral ear is also important to avoid operating on the better-hearing ear.
Although audiometric criteria can be defined quantitatively, the true art of patient selection is centered on computed tomographic (CT) evaluation of the middle ear and mastoid. Hypoplasia of the middle ear space, ranging from mild to severe, occurs in most cases of aural atresia, and ossicular development can be expected to correlate directly with middle ear size. The risk of surgical complications will be minimized and the chances for a successful hearing result increased if the middle ear and mastoid are aerated and at least two-thirds of the normal size, and if all three ossicles (although deformed) can be identified. Rarely, a well-developed middle ear/mastoid containing fluid will be encountered. To rule out a resolving otitis media or temporary eustachian tube dysfunction, a repeat scan 6 to 12 months later is recommended. Persistent middle ear fluid is a contraindication to surgery, although reassessment when the child is a teenager is reasonable.
It is important to demonstrate a patent oval window on CT. An absent oval window is more common in minor malformations21 (i.e., mild microtia, external auditory canal and tympanic membrane normal or only slightly small, conductive hearing loss) but can occur in aural atresia. Drilling a neo-fenestra, especially when the tympanic segment of the facial nerve is displaced inferiorly, and reconstructing with a prosthesis are associated with increased risks and decreased probability of long-term hearing improvement.
The position of the vertical segment of the facial nerve on the CT scan should be noted. Particular attention is paid to the area of the second genu. Extreme anterior displacement of the vertical segment restricts access to the middle space, increasing the chance of facial nerve injury during drilling of the canal and reducing the chance of a successful hearing result.
Recently, Jahrsdoerfer et al.12 developed a grading system that quantifies the developmental status of the atretic ear. This 10-point scale has been shown to predict postoperative hearing results. Using these strict selection criteria, only about 60% of patients with unilateral aural atresia are surgical candidates. The one exception to the audiometric and CT criteria reviewed above is the case of cholesteatoma developing in a severely stenotic external auditory canal. In such cases, surgery to address the cholesteatoma is mandatory; restoration of the conduction system depends on the degree of middle ear development and sensorineural function.
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