Martin Young and Sandy Chen Bush Veterinary Neurology Service, Leesburg, VA, USA The transzygomatic approach to intracranial surgery has been advanced and frequently modified over the last three decades in human medicine [1]. This technique provides excellent access to the middle fossa and the cavernous sinus [2]. Similarly, in veterinary medicine, this approach has been described by several authors with a variety of adaptations most commonly involving removal of a portion of the zygomatic arch [3–6]. The most common indication for this approach is neoplasia, such as a trigeminal nerve sheath tumor or piriform lobe glioma (Figure 25.1) [7, 8]. Both diagnostic biopsy and complete resection can be achieved through this corridor. Without the use of neuronavigational or intraoperative ultrasound equipment, knowledge and understanding of the regional anatomy is imperative. Figure 25.1 A T1+C transverse MRI image of a dog with a trigeminal nerve sheath tumor (arrow). The patient is shaved from the orbit to the level of the atlas vertebra on the appropriate half of the head. A headframe built by the authors as seen in Figure 25.2 was used to secure the patient’s head by the maxilla with the mandible hung open to move the ramus rostrally. The headframe is then rotated to a 45° angle until the central structure of the zygomatic arch is parallel to the surgery table (Figures 25.3). This improves the surgeon’s line of sight of the piriform lobe. The surgical site is then scrubbed and disinfected per normal standards of care. If a Styrofoam bead vacuum bag is used to position the head, a mouth gag should be used to help direct the ramus of the mandible rostrally. Care should be taken in cats as persistent use of a mouth gag has been associated with cortical blindness [9]. Figure 25.2 A stainless‐steel headframe made that allows rotation of the head for this procedure and secures the head in this position for the duration of the procedure. Figure 25.3 A headstand designed to securely position the patient for the transzygomatic approach. This patient is in sternal recumbency, and the head is positioned in a headstand with an approximate 45° rotation to the right to facilitate this approach to the left side. An incision is made between the lateral canthus and the tragus at the level of the dorsal aspect of the zygomatic arch (Figure 25.4). Caution must be taken at this level as the auriculopalpebral branches of the facial nerve (cranial nerve VII) and the auriculotemporalis nerve branches of the trigeminal nerve (cranial nerve V) are directly superficial to the dermis and transection can occur. The auriculopalpebral nerve crosses the zygomatic arch and continues to the orbit, and the auriculotemporalis nerve runs perpendicularly to the caudal aspect of the zygomatic arch and emerges between the masseter muscles [10]. Once identified, they can be gently dissected from the platysma and fascia to allow for light retraction and to avoid postoperative facial paralysis [6].
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Transzygomatic Approach to Ventrolateral Craniotomy/Craniectomy
Introduction
Patient Positioning/Preparation
Surgical Procedure
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