The dura mater of the temporal lobe has to be elevated from the bone of the temporal fossa and then split from the dura propria of the cavernous sinus; this permits to expose the elements of the sphenoidal fissure, the V2 and V3 branches of the trigeminal nerve (CN V), and the horizontal part of the internal carotid artery (ICA) [15]. Venous bleeding from the cavernous sinus can be controlled by fibrin glue injection inside the cavernous sinus. With such an exposure, a view is given on the superior aspect of the petrous bone up to its ridge (superior petrosal sinus). Therefore it provides access to the IAC, to the cochlea and semicircular canal (eminentia arcuata) from above (Fig. 10.3) [3], and to the petrous apex (Kawase approach). Drilling the petrous apex medial to the ICA, anterior to the cochlea and IAC and posterior to V3 (CN V), permits to reach some bone tumors such as chordomas or chondrosarcomas and some cysts like cholesterin cysts or granulomas and to expose partially or totally neuromeningeal tumors like CN V schwannomas or petroclival meningiomas.

The most frequent tumors for which intradural exposure is needed are meningiomas and neurinomas. So most of the time, it is achieved through a pterygoidal approach in which the temporal opening is more or less wide. Then a semicircular dural incision gives a dural flap reflected anteriorly, and a contraincision gives another flap reflected inferiorly. The temporal lobe is retracted with the help of gravity provided by an adequate head positioning. For an approach toward the anterolateral aspect of the brain stem, the sylvian fissure is widely opened. Drilling of the posterior clinoid process (the so-called transcavernous approach) may help in case of superior tumoral extension. For posterior approach, the tentorium has to be divided after coagulation and/or clipping of the superior petrosal sinus. This is done behind the oculomotor nerve (CN III) more or less close to it and after identification of the CN IV which should be separated from the tentorium.

In some cases the intradural exposure is combined with an extradural one (Fig. 10.2b); the dural incision on the temporal lobe is done horizontally, parallel to the superior petrosal sinus in order to protect the temporal lobe during its retraction; a blade is placed along the tentorium which is then cut. This allows to follow an intradural extension of a bone tumor (chordomas) or an infratentorial extension of a CN V neurinoma or of a meningioma [12, 15, 21].

Lateral approaches include all the routes going through the petrous bone [1, 2, 20]. They are usually named according to the petrous bone structures which are drilled out or preserved: the presigmoid retrolabyrinthine, translabyrinthine [7], transcochlear [13], and any combination up to total petrosectomy (Fig. 10.4). Obviously they require a perfect knowledge of the petrous bone anatomy or the assistance of an ENT surgeon. Most of them suppose the hearing function is lost or its sacrifice is accepted. The main problem in these approaches is the facial nerve (CN VII) which has generally to be preserved either by keeping it inside its bony canal (the fallopian canal) whenever possible or mobilized or even transposed.

Generally the patient is in the supine position with the head rotated toward the opposite side; a cushion under the shoulder is often useful to help the rotation and reduce the jugular vein compression and intracranial hypertension. An alternative is the lateral position. The skin incision is generally a C-shape one running around the auricle. For wide approaches, the external auditory canal may need to be cut at its bony-cartilaginous junction and closed in a blind sac fashion. The middle ear is then excluded with occlusion of the eustachian tube by a piece of muscle; it leads to the external semicircular canal. The drilling is then extended according to the selected approach. The dura mater of the posterior fossa and of the inferior aspect of the temporal lobe is usually exposed in between the superior petrosal sinus and its posterior limit the sigmoid sinus (SS).

Petrosal approaches are obviously used in bone tumors of the petrous bone. On the neurosurgical point of view, they are mostly utilized in acoustic neurinomas and in petrous bone meningiomas. In acoustic neurinomas (translabyrinthine approach), it gives a primary control onto the facial nerve and avoids cerebellar retraction; however the hearing function, if still present, is destroyed. In petrous bone meningiomas, the petrosal approaches lead directly to their zone of insertion [2, 12, 21, 23] with a similar strategy as the one applied in convexity meningiomas; the tumor is first devascularized before being debulked. The extent of drilling has therefore to be adjusted to this zone of insertion. For this, it is useful to classify petrous bone meningiomas in A, anterior to the IAC; B, at the level of the IAC; and C, posterior to the IAC; accordingly class A meningiomas need at least a transcochlear approach, class B a translabyrinthine one, and class C may be limited to a retrolabyrinthine one.

Besides the problem of the facial nerve preservation, the dural closure is the main concern since many air cells and often the eustachian tubes are opened. Dural closure generally needs to pack a fat pad which must be prepared.

These are the approaches passing behind the petrous bone essentially represented by the retro sigmoid approach (Fig. 10.1 left). This approach can be realized in the semi-sitting, lateral, or supine position. The semi-sitting position has the advantage of less amount of bleeding and a cleaner field as the blood is flowing down away from the area of work; however for long surgeries, it needs an arm rest to avoid fatigue and pain in the surgeon’s shoulders. Moreover air embolism is a possible complication. The lateral and supine positions are similar, the latter having the advantage to be more rapidly and simply achieved. In the supine positioning, the head is rotated toward the opposite side and tilted down a little (to see the tentorium). Rotation of the operating table must be possible during the surgery to better bring into view either the brain stem or the petrous bone. A cushion under the shoulder helps for the rotation as mentioned above. The lateral position is sometimes a better option when the tumor is on the right side (for a right-handed surgeon) since in the supine position, the shoulder of a short-neck patient is on the way of the hand holding the instruments. The skin incision is generally a C-shape one running around the auricle. The bone opening is on the occipital bone and the mastoid process so as to expose the lateral aspect of the posterior fossa up to the sigmoid sinus (SS) and the beginning of the transverse sinus. There is no benefit of skelotonizing the SS. The dura is opened in a semicircular fashion (concavity toward the SS) for an easy and watertight closure. This approach leads to the cerebellopontine angle (CPA) up to the tentorium and down to the jugular foramen area, the bone and dura opening being extended as required. Its main indications are CPA tumors (acoustic neurinomas, meningiomas, epidermoid cysts, etc.).

The drilling of part of the petrous bone may be required to access the inside of the IAC (drilling of the posterior wall of the IAC) or the Meckel cave and posterior part of the cavernous sinus (drilling of the petrous apex).

In some cases, it may be useful to combine the retrosigmoid approach to a retrolabyrinthine and/or a subtemporal approach. The SS can be either mobilized or even transsected [17] when there is a contralateral SS of good size; the superior petrosal sinus can be divided along with the tentorium enlarging the field superiorly.

The jugular foramen (JF) area is a challenging area in which three different types of tumors can be observed essentially: glomus tumors (paragangliomas), neurinomas, and meningiomas. These tumors can be classified according to their development related to the JF: type A, intradural tumors; type B, foraminal tumors; and type C, extracranial (cervical) tumors. In fact many tumors exhibit a combination of types with a type A-B-C at the maximum. Approaches to the JF must be decided following this classification; intradural tumors are exposed by a retrosigmoid approach extended inferiorly or sometimes combined with a foramen magnum opening; extracranial tumors need a lateral cervical opening which should permit a control of all the vasculo-nervous elements running in or close to the JF (ICA, internal jugular vein (IJV), CN IX to XII). Foraminal tumors have always a more or less important extension, the intradural or extracranial; the decision has to be made of the best choice between a retrosigmoid approach but without control of the distal part and an extracranial approach extended intracranially. There are mainly two extracranial approaches which can be used: the infratemporal and the juxtacondylar approaches.