Middle fossa approach: microsurgical anatomy and surgical technique from the neurosurgical perspective.
BACKGROUND
The purpose of this study was to call attention to the subtemporal approach directed through the petrous apex to the IAM. We studied the microsurgical anatomy of the middle floor to delineate a reliable angle between the GSPN and the IAM to precisely localize and expose the IAM from above. A new technique for the elevation of middle fossa floor in an anterior-to-posterior direction has also been examined in cadaveric dissections and performed in surgery.


METHODS
The microsurgical anatomy of the middle fossa floor was studied in 10 adult cadaveric heads (20 sides) after meatal drilling on the middle fossa. Five latex-injected specimens were dissected in a stepwise manner to further define the microsurgical anatomy of the middle fossa approach. The middle fossa approach is illustrated in a patient for the decompression of the facial nerve to demonstrate the surgical technique and limitations of bone removal.


RESULTS
Elevation of middle fossa dura in an anterior-to-posterior direction leads to early identification of the GSPN, where the nerve passes under V3. The most reliable and easily appreciated angle to be used in localizing the IAM is between the IAM and the long axis of the GSPN, which is approximately 61 degrees . Beginning drilling the meatus medially at the petrous ridge is safer than beginning laterally, where the facial and vestibulocochlear nerves become more superficial. The cochlea anteromedially, vestibule posterolaterally, and superior semicircular canal posteriorly significantly limit the bone removal at the lateral part of the IAM.


CONCLUSIONS
The surgical technique for the middle fossa approach which includes an anterior-to-posterior elevation of middle fossa dura starting from the foramen ovale and uses the angle between the IAM and the long axis of the GSPN to localize the meatus from above may be an alternative to previously proposed surgical methods.
Tanriover
Necmettin
N
Department of Neurosurgery, Cerrahpasa Medical Faculty, Istanbul University, Istanbul, Turkey. nctan27@yahoo.com
Sanus
Galip Zihni
GZ
Ulu
Mustafa Onur
MO
Tanriverdi
Taner
T
Akar
Ziya
Z
Rubino
Pablo A
PA
Rhoton
Albert L
AL
D000328:Adult; D001921:Brain / Q000033:anatomy & histology / Q000601:surgery; D002102:Cadaver; D035301:Cranial Fossa, Middle / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000601:surgery*; D004210:Dissection / Q000379:methods; D004388:Dura Mater / Q000033:anatomy & histology / Q000601:surgery; D007758:Ear, Inner / Q000033:anatomy & histology / Q000601:surgery; D005154:Facial Nerve / Q000033:anatomy & histology / Q000601:surgery; D005830:Geniculate Ganglion / Q000033:anatomy & histology / Q000601:surgery; D034381:Hearing Loss / Q000517:prevention & control; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008866:Microsurgery / Q000295:instrumentation / Q000379:methods*; D009464:Neuroma, Acoustic / Q000473:pathology / Q000601:surgery; D019635:Neurosurgical Procedures / Q000295:instrumentation / Q000379:methods*; D010579:Petrous Bone / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery; D011183:Postoperative Complications / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D019291:Skull Base / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery; D013346:Subarachnoid Space / Q000033:anatomy & histology / Q000601:surgery; D014057:Tomography, X-Ray Computed; D012668:Trigeminal Ganglion / Q000033:anatomy & histology / Q000601:surgery; D014276:Trigeminal Nerve / Q000033:anatomy & histology / Q000601:surgery; D000159:Vestibulocochlear Nerve / Q000033:anatomy & histology* / Q000601:surgery*