The Posterior Retrolabyrinthine Presigmoid Approach

34 The Posterior Retrolabyrinthine Presigmoid Approach

Marcio S. Rassi, Jean G. de Oliveira, and Luis A. B. Borba

Abstract

The posterior petrosal approach, also known as posterior retrolabyrinthine presigmoid approach, is indicated for lesions located in the petroclival junction, such as meningiomas, epidermoid tumors, trigeminal schwannomas, brainstem gliomas, brainstem cavernomas, and basilar trunk aneurysms. It allows full exposure of the middle and posterior fossae through the posterior mobilization of the sigmoid sinus, which is achieved by sectioning the tentorium.

The retrosigmoid approach can be easily associated with the presigmoid approach, widening the exposure inferiorly.

The surgery is performed parallel to the skull base, reducing the traction in the temporal lobe.

Keywords: posterior petrosal, petrosal approach, presigmoid, retrolabyrinthine, skull base, brain tumor

34.1 Background

The goal of any surgical approach is to achieve adequate exposure with minimum disturbance to the adjacent tissue. Selecting the appropriate approach depends on various factors including patient clinical characteristics, preoperative deficits, and tumor extension.

Working around the petrous temporal bone has been a challenge since the procedures described by Stieglitz et al, in 1896, and Fraenkel et al, in 1904.1 ^, ² However, the various morbidities such as blood loss and infection had put this technique to rest for the following decades, when finally, with the incorporation of the surgical microscope and development of refined microsurgical techniques, it was rediscovered by the surgical community.³ ^, ⁴ ^, ⁵

Between 1970 and the early 1990s, this approach underwent several modifications regarding the degree of brain retraction, transverse sinus preservation, and retrolabyrinthine drilling.⁶ ^, ⁷ ^, ⁸

Hakuba et al, in 1985, described the applicability of a transpetrosal-transtentorial approach for retrochiasmatic craniopharyngiomas,⁹ which was lately adopted by several authors.¹⁰ ^, ¹¹ ^, ¹² The technique, as we perform with minimum modifications, was described by Al-Mefty et al in 1988 for petroclival meningiomas. The authors reported the advantage of avoiding retraction over the cerebellum and temporal lobe, early access to the blood supply of tumors, and avoiding the sacrifice of vital structures such as the cochlea, labyrinth, facial nerve, transverse and sigmoid sinuses, and vein of Labbé.⁸ Also, this approach offers the possibility of accessing both pre- and retrosigmoid area and mobilizing the sigmoid sinus through cutting the tentorium, achieving maximum exposure.¹³

34.2 Indications

The posterior petrosal approach is suitable for lesions located in the petroclival junction, such as meningiomas, epidermoid tumors, trigeminal schwannomas, brainstem gliomas and cavernomas, and basilar trunk aneurysms.

It incorporates all the advantages of the retrosigmoid approach and all the advantages of the anterior petrosal approach, allowing the surgeon to freely work from cranial nerves (CNs) III to XII.

The coagulation and cut of the superior petrosal sinus (SPS) and tentorium communicate the supra- and infratentorial compartments, and maximum exposure is achieved by mobilizing the sigmoid sinus posteriorly.

The subtemporal route of this approach can extend anteriorly exposing the floor of middle fossa, the lateral wall of the cavernous sinus, and the mesencephalic, crural, and carotid cisterns.

34.3 Surgical Technique

34.3.1 Patient Positioning

The patient is placed in a true lateral position. The ipsilateral shoulder is slightly displaced inferiorly and anteriorly, and the head is slightly rotated ipsilaterally to the keep it parallel to the floor and fixed in a three-point headrest. The contralateral arm is supported in a 30-degree angle to ensure venous output. The abdominal region and lateral aspect of the thigh are prepped for eventual fat and facia lata harvest, respectively (Fig. 34.1).

Fig. 34.1Patient positioning. The patient is placed in a true lateral position. The contralateral arm rests in a 30-degree angle with the floor.

34.3.2 Soft Tissue Work

Skin incision begins at the level of the posterior root of the zygomatic arch, ascending 2 cm cranially, turning posteriorly around the pinna parallel to the temporal line and caudally, running 3 cm posterior to the external auditory meatus, until reaching 1 cm below the mastoid tip. The skin flap is elevated and retracted anteriorly and inferiorly. The superficial fascia of the temporal muscle is dissected from the muscle fibers and mobilized inferiorly contiguous to the suboccipital muscles and sternocleidomastoid muscle. The posterior aspect of the temporal muscle is dissected from the temporal squama and displaced anteriorly (Fig. 34.2).

Fig. 34.2Cadaveric demonstration. (a) Skin incision. (b) Following subcutaneous dissection, the temporal muscle fascia (TMF) is identified along with the sternocleidomastoid muscle (ECM). (c) The TMF is elevated exposing the temporal muscle (TM) fibers. (d) The TMF is kept attached to the ECM and craniocervical muscles which are mobilized inferiorly.

34.3.3 Bony Work

Mastoidectomy

There are two ways to begin the bony work: with the cranial flap or with the mastoidectomy. The authors prefer to perform the mastoidectomy first because we believe it allows early identification of the position of the sinuses and the possibility of a wider dissection of the dura from the bone flap before running the craniotome.

First, we define the limits of the mastoidectomy by drawing three lines. The first line is parallel to the posterior root of the zygoma, crossing posteriorly and delimitating the superior limit of mastoid cavity and the floor of middle fossa. The second line crosses parallel to the posterior wall of external auditory meatus. The third line crosses posteriorly, delimitating the posterior limit of mastoid cavity. The cortical bone of mastoid can be either drilled out or removed in one piece for further reconstruction. The air cells should be totally exposed and removed with a high-speed drill until the whole extension of the sigmoid sinus, superior petrosal sinus, floor of middle fossa, posterior semicircular canal, and pre- and postsigmoid dura mater have been skeletonized (Fig. 34.3).

Cranial Flap

Whenever possible we prefer a single burr hole over the medial aspect of the transverse sinus, from which we run the craniotome superiorly and inferiorly, creating a single bone flap that includes the supra- and infratentorial compartments. After elevating the flap, the remaining bone over the sigmoid sinus is removed until reaching the jugular bulb, totally exposing the presigmoid dura. At this stage, the dura over the basal temporal lobe and the pre- and postsigmoid spaces should be widely exposed (Fig. 34.4).