Surgical approach to the internal auditory meatus in acoustic neuroma surgery: significance of preoperative high-resolution computed tomography.
OBJECTIVE
To establish a surgical approach that provides better access to the internal auditory meatus (IAM) in acoustic tumor removal via a suboccipital transmeatal route, the anatomic location of the labyrinth with regard to the sigmoid-fundus line and the extent of bone removal from the IAM were evaluated by pre- and postoperative high-resolution computed tomography for 47 patients.


RESULTS
The labyrinth was located lateral to the sigmoid-fundus line in 22 cases (lateral type, 46.8%), on the line in 9 (on-the-line type, 19.1%), and medial to the line in 16 (medial type, 34.0%). Postoperative high-resolution computed tomography showed that the mean length of the posterior wall from the fundus was shortened to 5.1 +/- 1.1 mm (n = 27) in the partially resected group and to 2.0 +/- 0.6 mm (n = 20) in the widely opened IAM group. The labyrinth was damaged in four cases from the widely opened IAM group; the preoperative status of the labyrinth was medial to the sigmoid-fundus line in three and on the line in one. The cochlear nerve was preserved in seven (31%) partially resected and in eight (50%) widely opened IAM cases. The overall success rate of hearing preservation was 4 of 22 (18.2%) partially resected and 5 of 16 (31.2%) widely opened cases.


CONCLUSIONS
Preoperative evaluation of the anatomic relation between the IAM and the labyrinth by high-resolution computed tomography provides an efficient surgical approach to the IAM and contributes to anatomic and functional preservation of the cochlear nerve.
Department of Neurosurgey, Hamamatsu University School of Medicine, Japan.
T
T
Yokoyama
K
K
Uemura
H
H
Ryu
K
K
Hinokuma
S
S
Nishizawa
S
S
Yamamoto
M
M
Endo
K
K
Sugiyama
D005260:Female; D006309:Hearing; D006801:Humans; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000000981:diagnostic imaging* / Q000601:surgery*; D011184:Postoperative Period; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome