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.
Yokoyama
T
T
Department of Neurosurgey, Hamamatsu University School of Medicine, Japan.
Uemura
K
K
Ryu
H
H
Hinokuma
K
K
Nishizawa
S
S
Yamamoto
S
S
Endo
M
M
Sugiyama
K
K
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