Background

Preservation of hearing has become the most challenging goal of intracanalicular acoustic tumor surgery. The reported hearing preservation after microsurgical excision of intracanalicular tumors varies from 12% to 82%.2,5-10 In 1969, House and Hitselberger6 first reported that they obtained functional hear ing preservation in four out of five patients with intracanalicular tumors excised via the middle fossa approach. Ten years later, Brackmann11 reported "some" hearing preservation in 5 out of 11 patients using this approach. Subsequently many surgeons further refined the middle fossa approach and reported better hearing preservation rates.12 Both Silverstein et al.9 and Jannetta et al.13 used the retrosigmoid approach in order to achieve hearing preservation. Sterkers et al.10 had a 66.7% hearing preservation rate using the retrosigmoid approach. Nadol et al.14 reported a 50% useful hearing preservation rate but included patients with a speech discrimination score (SDS) as low as 15% and a speech reception threshold (SRT) of < 70 dB in the useful hearing group. They also reported that 36% (5/14) had hearing preservation. Preserved hearing was defined as a change of < 15 dB in SRT and < 15% in SDS, as compared with preoperative levels.14,15

Samii et al.5 recommended early surgery by the retrosigmoid approach in order to improve hearing preservation rates. In a review of 1000 acoustic tumors, Samii et al.5 reported a 46% (17/37) hearing preservation rate in the subgroup of patients who had intracanalicular tumors. Samii et al.5 advocated the Hannover classification, which included patients with PTA levels as poor as 80 dB and speech discrimination scores as low as 10%, in the preserved hearing group. Useful hearing preservation (defined as PTA < 40 and SDS > 70%) was noted to be 29%.16 Haines et al.2 reported an 82% (9/11) hearing preservation rate using both middle fossa (5/6) as well as retrosigmoid approaches (4/5), although in the next few patients hearing was not preserved so readily (personal communication). Irving et al.7 compared hearing preservation rates (based on the 50/50 rule) using either a middle fossa or a retrosigmoid approach. They reported a 44% useful hearing preservation rate in the middle fossa group as compared with 12% in the retrosigmoid group. They concluded that the middle fossa approach has enhanced lateral exposure that facilitated lateral to medial dissection and promoted development of tumor arachnoid planes at the fundus. They hypothesized that this results in less traction on the distal cochlear nerve at its weakest point where it forms fine filaments in the modiolus and also less traction on the distal labyrinthine artery at its foraminal end.7

Most of the reported hearing preservation rates reflect immediate postoperative hearing status but do not document long-term hearing outcome at 1 or more years after surgery. Long-term follow-up of patients with preserved postoperative hearing showed delayed hearing loss in a significant number of patients.17'18 Shelton et al.18 reported further loss of preserved postoperative hearing in 56% of patients over a mean follow-up of 8 years.18

Facial nerve function has not been documented in most of the hearing preservation studies. Nadol et al.14 observed postoperative facial paresis in 4 of 14 patients of smaller acoustic tumors that recovered in a year. Atlas et al.19 described 3 patients with House-Brackmann grade II results and 2 with grade III results. Cohen and Ransohoff20 reported a single intracanalicular tumor patient with preserved hearing; this patient had partial facial weakness with incomplete recovery. Irving et al.7 noticed an increased incidence of transient facial nerve palsy after middle fossa surgery in the immediate postoperative phase.

and sagittal reconstructed stereotactic images. A conformational plan is achieved using 1 to 6 isocenters of 4-mm beam diameter. After finalizing the plan, a maximum dose to the tumor margin is determined. The treatment isodose, maximum dose, and dose to the margin are jointly decided by a neurosurgeon, radiation oncologist and medical physicist after analysis of the hearing status of each patient. Since 1994, we have prescribed 13 Gy to the tumor margin in patients with serviceable hearing in an effort to preserve their hearing. Radiosurgery is performed with a 201-source cobalt-60 Leksell Gamma Knife (model U or B, Elekta Instruments, Atlanta, GA) by positioning the target serially at x-, y-, and z-coordinates of each isocenter. The stereotactic frame is removed immediately afterward, and the patients are discharged within the next 6 to 18 h.

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Hearing Aids Inside Out

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