Cristian Gragnaniello, Parisa Sabetrasekh, Sam Maghami, Alan Siu, Zachary Litvack, and Ashkan Monfared

35.1 Introduction

Presigmoid approaches decrease the working angle and depth of field as compared to retrosigmoid approaches, and are indicated for extra-axial lesions anterolateral to the brainstem, petroclival lesions, or deep-seated brainstem lesions. Common pathologies in the internal auditory canal (IAC) and cerebellopontine angle (CPA) include vestibular schwannomas, meningiomas, and epidermoids. These approaches can also be combined with a middle fossa craniectomy for lesions extensively involving the temporal bone or spanning both sides of the tentorial incisura.

The translabyrinthine and transcochlear approaches are variations of a posterior transpetrosal approach, which provide access to the IAC and CPA. These approaches are usually used in patients in whom the hearing is already compromised. In the translabyrinthine approach, the labyrinth is removed, sacrificing hearing if present, to provide an anterolateral view of the CPA without cerebellar retraction.

The transcochlear approach, with or without transposition of the facial nerve (placing the VII cranial nerve at increased risk for iatrogenic injury), provides additional access to the mid-clivus, petrous apex, and pre-pontine cistern.

35.2 Indications

• Lesions of the internal auditory canal or cerebellopontine angle.

• Anterior and ventral brainstem lesions in patients with non-serviceable hearing.

• Deep-seated brainstem lesions.

• Petroclival lesions.

• Tumors extending into the cochlea.

• Tumors extending into the temporal bone.

• Tumor remnants from a previous retrosigmoid or middle fossa approach.

35.3 Patient Positioning

Patients may be positioned supine, lateral, or ¾ prone (aka park-bench) at the discretion of the surgeon.

Supine position is preferred when possible as it minimizes the risk of pressure ulcers and positional neuropathies, but requires a patient with good cervical range of motion, and can be difficult in obese patients or those with broad shoulders.

If not supine, we prefer ¾ prone to lateral as it drops the shoulder out of the field, increasing the angle of attack toward the tentorium.

35.3.1 Supine

• Position: The patient is positioned supine and the head is not pinned (i.e., placed on a foam donut or a cerebellar headrest).

• Body: The shoulders and body remain parallel to the floor. The elbows are padded and the arms tucked against the body.

• Head: The head is rotated 60° contralateral to the side of the pathology. The auricle of the ear may be folded over the external canal and taped.

• The external ear is the highest point in the surgical field.

35.3.2 Three-Quarters Prone

• Position: The patient is positioned three-quarters prone, with the head fixed in a Mayfield head holder.

• Body: The body is held in place with a sandbag. An axillary roll is placed about 5 cm below the axilla. The dependent arm is placed in a sling, and the upper arm placed on an armrest. A pillow is placed in between the legs with the top leg flexed 45°. Extensive padding is used on the elbows, hands, hips, knees, ankles, and areola of the breasts to prevent pressure ulcers.

• Shoulder: The shoulder is taped downward and away from the ear to minimize hindrance.

• Head: The head is rotated 45° contralateral to the side of the pathology.