38 Transotic Approach for Vestibular Schwannoma Resection

10.1055/b-0039-169192

38 Transotic Approach for Vestibular Schwannoma Resection

Edwin M. Monsell, Yin Xia, and Ugo P. Fisch

38.1 Introduction

In 1979, Ugo Fisch introduced the transotic approach to improve surgical exposure and other aspects of the translabyrinthine approach of William House. The translabyrinthine approach is primarily a posterior approach to the internal auditory canal (IAC) and cerebellopontine angle, whereas the transotic approach is the widest lateral approach, bounded by the sigmoid sinus, the superior petrosal sinus, the internal carotid artery, and the jugular bulb (Fig. 38‑1 , Fig. 38‑2 ). The transotic approach also incorporates a subtotal petrosectomy, which may reduce the risk of cerebrospinal fluid (CSF) leakage and associated intracranial infection. Today, the translabyrinthine and retrosigmoid approaches are the most commonly used, though the transotic approach continues to have significant advantages in cases of constricted temporal bone anatomy, including cases with a high jugular bulb, prominent or anteriorly located sigmoid sinus, low tegmen, or a combination of these variations. The extra time required to develop the transotic approach compared to the translabyrinthine approach is at least partially mitigated because less time is required for tumor removal. The transotic, like the translabyrinthine approach, does not spare hearing, so it is only used when there is no intent to preserve hearing in the operated ear.

**Fig. 38.1** Diagrammatic view from the superior position showing the exposure of the translabyrinthine approach (left) and the wider transotic approach (right), redrawn from Chen and Fisch.² AN, acoustic neuroma (vestibular schwannoma); C, carotid artery; CER, cerebellum; CVN, cochlear-vestibular nerve; EAM, external auditory meatus; FN, facial nerve; ME, middle ear; SS sigmoid sinus in an unusually anterior position that constricts the translabyrinthine exposure.

**Fig. 38.2** Intraoperative photomicrograph in a case of right vestibular schwannoma with a large, anterior sigmoid sinus (large blue object in the foreground, SS). The white measuring tape passes medial to the mastoid segment of the facial nerve. In this case the approach provides 4 mm of posterior and 12 mm of anterior exposure from the facial nerve. FC, fallopian canal of the facial nerve; ICA, internal carotid artery; MFD, middle fossa dura. (Reproduced with permission from Fisch and Mattox.s. Literatur)

In the transotic approach, the entire circumference of the IAC is exposed except for a bar of bone that protects the meatal segment of the facial nerve superiorly. The transotic approach provides an improved direct view of the intracranial course of the facial nerve, including the interface between the tumor and the facial nerve just proximal to the porus acusticus, where most injuries to the nerve occur. In the transotic approach, the facial nerve is extensively skeletonized but left in place; however, in the transcochlear approach of House and Hitselberger, it is transposed posteriorly to help expose the clivus, a maneuver that increases the risk of facial nerve injury.

38.2 Surgical Technique

38.2.1 Preparation

The patient is positioned in the supine position with the head turned 45 degrees away, and general anesthesia is induced. A neurosurgical head holder may be used. The hair surrounding the surgical site is clipped close to the skin widely above and behind the pinna. The surgical site is prepared with povidone-iodine scrub and paint. The abdomen is prepared for harvesting abdominal fat. The contralateral leg is prepared if a sural nerve graft is anticipated. The facial nerve is monitored.

38.2.2 Skin Incision

The operative techniques for the subtotal petrosectomy and transotic approach are described in detail with indications for surgical instrumentation in Microsurgery of the Skull Base by Fisch and Mattox, from which most of the illustrations in this chapter are reproduced.s. Literatur The skin incision begins superior to the pinna (Fig. 38‑3 ), continues behind the postauricular hairline, and extends over the mastoid tip. The superior portion of the incision (Fig. 38‑3 ) is made after tumor resection, and provides exposure to develop the temporalis muscle flap.

**Fig. 38.3** The postauricular incision used for the transotic approach. (Reproduced with permission from Fisch and Mattox.s. Literatur)

38.2.3 Blind Sac Closure of the External Auditory Canal

A mastoid periosteal flap is developed (Fig. 38‑4 ). The external auditory canal (EAC) is transected at the bony–cartilaginous junction. The EAC skin is separated from the cartilage, everted externally, and closed with sutures. The periosteal flap is rotated to cover the lateral end of the EAC, and is sutured to the EAC cartilage (Fig. 38‑4 ). This creates a watertight closure of the EAC. The skin of the EAC is elevated to the annulus, the middle ear space is entered, and the chorda tympani nerve is divided. The incudostapedial joint is separated and the malleus neck is cut. The tympanic membrane, manubrium, and remaining EAC skin are removed as a continuous block of tissue. The operative site is again carefully inspected to be sure that all squamous epithelium has been removed, because the cavity will be obliterated (Fig. 38‑5 ).

**Fig. 38.4** The periosteal flap is located inferiorly from the temporal line, and is pedicled anteriorly to the soft tissues posterior to the auricle. (Reproduced with permission from Fisch and Mattox.s. Literatur)

**Fig. 38.5** The ossicular chain is separated and the chorda tympani nerve is sectioned. The tympanic membrane, fibrous annulus, and remaining skin of the external auditory meatus are removed en bloc. (Reproduced with permission from Fisch and Mattox.s. Literatur)

38.2.4 Subtotal Petrosectomy

The inferior temporalis muscle is elevated off the squamous temporal bone to facilitate exposure of the tegmen in the mastoid, and the attachments of the sternocleidomastoid muscle are removed to expose the entire mastoid tip. A complete mastoidectomy is carried out (Fig. 38‑6 ). The EAC wall is removed and lowered to the level of the facial nerve. All accessible air cells are systematically and completely exenterated. The tympanic end of the eustachian tube is opened to the isthmus and obliterated. The mastoid tip is removed (Fig. 38‑6 ).