Definition
Following the extended cortical mastoidectomy and exenteration of the posterior part of the labyrinth, exposure of the internal auditory canal, and cerebellopontine angle through the posterior cranial fossa.
Indications
The main indication of this technique is in acoustic neuroma surgery where the hearing is not of concern. However, it may also be carried out for different neurotologic procedures.
Anatomical Orientation
Surgical Steps
A classical cortical mastoidectomy, including posterior tympanotomy has been carried out. The temporal bone is ready for the main steps of the translabyrinthine approach. The limits of the approach are indicated in the figure.
EAC: External auditory canal
MCF: Middle cranial fossa (dural plate)
MT: Mastoid tip
SS: Sigmoid sinus (dural plate)
ZR: Zygomatic root
First, the interlabyrinthine cells are drilled away using a medium-sized cutting burr. Note that the mastoid in this temporal bone is contracted, which means that the sigmoid sinus is located anteriorly and the dura of the middle cranial fossa is located inferiorly.
II: 3–4mm cutting burr
MIL: Posterior labyrinth (HSC, SSC, PSC)
Next, the retrolabyrinthine cells are exenterated using the same cutting burr. In such a contracted mastoid, turning the temporal bone toward the surgeon in the laboratory or tilting the operating table during surgery, would prevent having to work blindly.
ILC: Interlabyrinthine cells
RLC: Retrolabyrinthine cells
Definitions and Tips
- Lateral skull base surgery can be perceived as an extension of the classical tympanomastoid procedures. In this manner, the translabyrinthine approach is an extension of a cortical mastoidectomy and the transotic approach is an extension of a radical mastoidectomy.
- Labyrinth (otic capsule): Definition: The inner ear. Tips: The labyrinth is traditionally described as consisting of two parts; the anterior labyrinth and the posterior labyrinth. The anterior labyrinth, i.e., the anterior otic capsule, is formed by the cochlea. The posterior labyrinth, i.e., the posterior otic capsule, is formed by the vestibule and semicircular canals.
The sinodural angle is delineated by first using a medium-sized cutting burr, then a diamond burr. The superior petrosal sinus, which runs along the sinodural angle inside the dura, should always be kept in mind and the drilling executed with care.
II: 3–4mm cutting and diamond burrs
MIL: Sinodural angle
The microsurgical instrument is pointing to the exposed digastric ridge. The three semicircular canals are also displayed in this figure, where the next steps of the approach will be carried out.
HSC: Horizontal semicircular canal
MFN: Mastoid facial nerve
PSC: Posterior semicircular canal
SSC: Superior semicircular canal
Following complete exenteration of the interlabyrinthine, retrolabyrinthine, and retrofacial cells and delineation of the neighboring structures, the cavity has been enlarged from a classical cortical mastoidectomy to an extended cortical mastoidectomy. Note that the facial canal and all the semicircular canals have been skeletonized.
I: Incus
RFC: Retrofacial cells (removed)
SDA: Sinodural angle
Definitions and Tips
- In the translabyrinthine approach, each anatomical structure should be used as a reference for locating the subsequent structure. Otology-neurotology and skull base surgery is based on moving from one landmark to the other. Ulug et al. showed that each anatomical structure of the cranium can be used as a landmark to define the next structure. (Ulug T, Sahinoglu K, Ozturk A, Ari Z. Surgical landmarks during mastoidal and petrosal operations. Okajimas Folia Anat Jpn 1998;75: 163–166.)
