Posterior and Combined Petrosal Approaches

Fig. 4.1

The skin incision is made starting from the zygomatic arch approximately 1 cm anterior to the tragus and extending superiorly just behind the hairline. The incision curves posteriorly about two finger breadths above the pinna and two finger breadths behind the mastoid before curving caudally. For the combined petrosal approach, the incision is carried anteriorly to provide additional access to the middle cranial fossa (blue dotted line); for the posterior petrosal approach, the incision does not need this additional curve and is carried up from the zygoma (red dotted line). Both incisions have a common posterior limb (black dotted line)

Burr holes are placed rostral and caudal to the transverse sinus, one set laterally just behind the level of the sigmoid sinus and one set medially as allowed by the exposure for a total of four burr holes. A drill with a footplate attachment is used to liberate the temporal and occipital portions of the craniotomy, while a drilling burr is used to connect the cuts overlying the sinus. Once the craniotomy is completed and the bone flap is elevated, a mastoidectomy is pursued in order to fully skeletonize the sigmoid sinus to the level of the jugular bulb and expose the presigmoid dura (Figs. 4.2 and 4.6). The mastoid cortex is removed en bloc prior to starting the mastoidectomy and saved along with the craniotomy flap for eventual reconstruction. The otic capsule and fallopian canal are left untouched in order to protect hearing and facial nerve function, respectively (Fig. 4.2, inset; Fig. 4.6b).

Fig. 4.2

Burr hole placement and craniotomy cuts shown in the main figure. The cuts overlying dura are made with a craniotome attachment, while those overlying the sinus are made with a drilling burr (2). Inset shows the mastoidectomy which is performed subsequent to the craniotomy. The facial nerve (FC) and the semicircular canals (SC) are shown here for reference but are not exposed during the surgical approach in order to protect them. TM temporalis muscle, SM sternocleidomastoid muscle (Reproduced with permission from Al-Mefty [18])

Fig. 4.3

The dural opening are shown. Linear dural openings are made along the floor of the middle fossa (TD) as well as in the presigmoid dura (PFD). The inset demonstrated ligation and sectioning of the superior petrosal sinus (PS), which allows subsequent sectioning of the tentorium and mobilization of the sigmoid sinus (SS) (Reproduced with permission from Al-Mefty [18])

Fig. 4.4

The additional exposure afforded by sectioning of the tentorium and mobilization of the sigmoid sinus (SS). Cranial nerves 3–12 can be exposed (roman numerals). The inset shows the technique of identifying the fourth prior to completion of tentorium division (T) in order to protect it (Reproduced with permission from Al-Mefty [18])

Fig. 4.5

Closure . The previously reserved pedicled temporalis fascia is placed along the floor of the middle fossa and secured with suture, clips and/or fibrin glue (Reproduced with permission from Al-Mefty [18])

Fig. 4.6

3D reconstruction using segmentation of brain MRI for a patient who underwent a combined petrosal approach for resection of a petroclival meningioma. (a) A full 3D reconstruction prior to the craniotomy showing the location of the dural sinuses (blue), tumor (green), and the arterial system (red). (b) 3D reconstruction following the combined supratentorial and infratentorial craniotomy and mastoidectomy with the head in the surgical position. Tumor (green) presence in the posterior and middle cranial fossae is well demonstrated. Presigmoid (blue) access to the tumor is limited. The tentorium (brown) and the arterial vasculature (red) are also shown. (c) 3D reconstruction after the tentorium (brown) has been cut allowing the sinus (blue) to be mobilized. The maneuver allows full access to the tumor (green) without the need for retraction. The arterial vasculature (red) is also shown. (d) Volumetric 3D reconstruction of the tumor (green), dural venous sinuses (blue), and the arterial vasculature (red) is shown with the three orthogonal MRI planes in order to demonstrate their relationship to the surrounding brain parenchyma

Dura opening proceeds by creating a linear incision along the floor of the middle cranial fossa and extending the opening back toward the tentorium, carefully preserving underlying venous anatomy (Fig. 4.3). Another dural opening is made in the presigmoid dura and expanded toward the tentorium; this step often results in sectioning of the endolymphatic sac. Once the tentorium is exposed from above and below, the superior petrosal sinus is controlled with coagulation, and the tentorium is incised with careful attention not to compromise any temporal lobe veins (Fig. 4.3, inset). Attention is given to the trochlear nerve at the medial tentorial edge, which often lies just above the level of the tentorium. In cases of tentorial meningiomas, the tentorium is excised instead of cut. Once the cut reaches the incisura, the sigmoid sinus is liberated and may be retro-displaced which significantly increases the presigmoid working room afforded by the exposure (Figs. 4.4 and 4.6c) Microsurgical tumor resection may now proceed (Fig. 4.6d).

Combined Petrosal Approach

Patient Positioning

The patient is positioned in the same way as described for the posterior petrosal approach.

Skin Incision and Craniotomy

The skin incision is similar to that described for the posterior petrosal with slightly more anterior bias of the anterior-most limb to allow additional exposure of the middle fossa (Fig. 4.1).

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