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Translabyrinthine Approach

In the translabyrinthine approach, the internal acoustic canal and cerebellopontine angle are approached through a mastoidectomy and labyrinthectomy. There are two goals of bone removal in this approach. The first is to remove enough bone to be able to identify the nerves lateral to the tumor as they course through the internal auditory canal and by the transverse and vertical crests. The second is to expose the dura on the posterior aspect of the temporal bone that faces the cerebellopontine angle. The triangular patch of dura facing the cerebellopontine angle. called Trautmann's triangle, extends from the sigmoid sinus laterally to the superior petrosal sinus above and the jugular bulb below.

In the translabyrinthine exposure, the mastoid cortex is opened and the exposure is directed through the triangular gateway between the facial nerve anteriorly. the sigmoid sinus posteriorly and floor of the middle fossa above. Bone is removed to expose the dura covering the sigmoid sinus and middle fossa, the facial nerve, the angle between the sigmoid sinus and middle fossa dura (called the sinodural angle), and the upper surface of the jugular bulb. The mastoidectomy is carried down to the horizontal semicircular canal, which provides the landmark for identifying the other canals and the facial nerve.

The labyrinthectomy portion of the procedure involves removing the semicircular canals and vestibule to expose the dura lining the internal auditory canal. In the process of removing the semicircular canals, the dura of the middle fossa above the internal acoustic meatus is skeletonized and the dura on the posterior fossa plate behind the canal is exposed. After opening and removing the canals, the vestibule is opened and removed, and the dura lining the posterior half of the internal auditory canal is exposed. Care is required to avoid injury to the facial nerve as it courses below the horizontal canal and the ampulla of the posterior canal and around the superolateral margin of the vestibule. Further bone removal at the lateral end of the canal exposes the transverse and vertical crests and the covering of the superior and inferior vestibular and facial nerves. In removing bone behind the internal acoustic canal, it is important to remember that the jugular bulb may bulge upward behind the posterior semicircular canal or internal auditory meatus. The vestibular aqueduct and endolymphatic sac will be opened and removed as bone is removed between the meatus and the jugular bulb. The cochlear canaliculus will be seen deep to the vestibular aqueduct as bone is removed in the area between the meatus and the jugular bulb. The lower end of the cochlear canaliculus is situated just above the area where the glossopharyngeal nerve enters the medial side of the jugular foramen.

The subarcuate artery or the anterior inferior cerebellar artery may be encountered in the dura of Trautmann's triangle. Commonly, the subarcuate artery, which arises from the anterior inferior cerebellar artery, passes through the dura on the upper posterior wall of the meatus as a fine stem but, on occasion, the subarcuate artery along with its origin from the anterior inferior cerebellar artery may be incorporated into the dura and dip into the subarcuate fossa, on the posterior face of the temporal bone.

 
 

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