Suboccipital Craniectomy: Retromastoid Approach for Acoustic Schwannoma

Abstract

The most common position for posterior fossa operations in adults is the lateral decubitus or “park bench” position; this approach has largely replaced the use of the sitting position for most procedures. After intubation and placement of a three-point head fixation device, the patient is turned on his side and the shoulder contralateral to the lesion supported by a roll in the axilla; the ipsilateral shoulder is rolled forward and pulled down with tape (Fig. 25-1). The dependent arm can be suspended by a sling in the crook of the Mayfield attachment. All pressure points are carefully padded. In lesions of the cerebellopontine angle, the head is kept in a relatively neutral position and the body is slightly elevated (reverse Trendelenberg). A straight retromastoid incision is used for most lesions centered on the internal acoustic meatus and for exploration of the cranial nerves (see Chapter 26). The incision is usually 8 to 10 cm long and is made one fingerbreadth medial to the mastoid process and digastric groove (Fig. 25-2). The incision extends from a line just above the top of the pinna of the ear to a point just below the mastoid tip. Care in splitting the muscle at the inferior end is important in avoiding an ectactic vertebral artery. For very large lesions, the superior end of the incision can be extended medially to a point 2 cm above the inion and curved toward the midline (inverted hockeystick) (Fig. 25-3). Once the linear retromastoid incision is cleared down to the bone, it can usually be held open by one or two curved cerebellar retractors.