For the middle fossa craniotomy, the surgeon sits at the head of the table, and the microscope is off to the side. The ipsilateral scalp is shaved to accommodate the incision, which begins at the pretragal area and extends superiorly 7–8 cm with a gentle curve anteriorly (Fig. 3.1). The incision should begin at the inferior border of the tragus and be immediately anterior to the tragus, placed in a pretragal skin crease. The pretragal skin crease placement minimizes the cosmetic impact of this facial incision. By extending the incision to the inferior border of the tragus, one can expose the floor of the middle fossa more easily. Plastic adhesive drapes are applied; the skin and plastic drapes are scrubbed with Betadine and blotted dry. Towels are placed encompassing the temporoparietal scalp, including the auricle and zygomatic arch. An adhesive craniotomy drape is placed and cut away to expose the skin prior to making the skin incision. Intraoperative mannitol is given to decrease intracranial CSF pressure and to facilitate temporal lobe retraction. The skin incision is made with a No. 15 blade, and the temporalis muscle and fascia are divided with electrocautery and retracted with an Adson Cerebellar Retractor to expose the calvarium. The craniotomy opening is made in the squamous portion of the temporal bone, measuring approximately 5 × 5 cm and located approximately two thirds anterior and one third posterior to the external auditory canal (EAC) or centered at the root of the zygoma. Anterior and inferior placement of the craniotomy is critical to ensure adequate exposure, particularly when operating on the left ear. The bone flap is based at the root of the zygoma as close to the floor of the middle fossa as possible and can be fashioned with a high-speed drill using a footplate attachment to protect the underlying dura. The dura is initially exposed in two corners of the bone flap diagonal to one another, which allows separation of the dura from the flap and introduction of the footplate drill. Care must be taken when creating the bone flap to avoid lacerating the dura, and the extradural position of the footplate should be confirmed periodically while drilling. It is sometimes necessary to remove additional bone along the middle fossa floor with a cutting burr or rongeur once the craniotomy window is removed. An alternative technique is to outline the entire craniotomy flap with a high-speed drill using standard cutting followed by diamond burrs. The bone flap is set aside for replacement later.

The dura is elevated from the floor of the middle fossa with a suction irrigator and a blunt dural elevator, with the initial landmark being the middle meningeal artery. This marks the anterior extent of the dissection. If venous bleeding is encountered in the area, it can be controlled with either a slurry of powdered absorbable gelatin sponge (Gelfoam) and thrombin or absorbable knitted fabric (Surgicel). Dissection of the dura proceeds in a posterior-to-anterior direction to protect against injury to a potentially dehiscent geniculate ganglion, which is seen in 5% of cases. The petrous ridge is then identified posteriorly, and the superior petrosal sinus is elevated from its groove at the time the true ridge is identified. The arcuate eminence and greater superficial petrosal nerve (GSPN) are identified, which are the major landmarks in the intratemporal portion of the dissection.

Once the dura is elevated, the Layla retractor is placed over the medial ridge of the superior petrosal sinus and locked in place to support the temporal lobe. An alternative is the House-Urban retractor, however the Layla retractor has a lower profile and dual retractor blades to support the widely elevated temporal lobe (Fig. 3.2) [38]. The GSPN is located medial to the middle meningeal artery (Fig. 3.3). A large diamond drill with continuous suction irrigation is used to identify the superior semicircular canal. Once this is skeletonized and followed anteriorly, the geniculate ganglion is identified. As described by Garcia-Ibanez, the IAC is located at the bisection of the angle formed by the GSPN and the superior semicircular canal [39]. Bone is removed at the medial aspect of the petrous ridge at this bisection, identifying the IAC. This is taken laterally in the same axis of the external auditory canal, exposing the dura of the posterior fossa widely (2 cm), and the porus acusticus is exposed for 270° circumferentially. As the lateral IAC is approached, the surgical field tightens with the labyrinthine portion of the facial nerve lying immediately posterior to the basal turn of the cochlea. The dissection must consequently narrow to approximately 90° to avoid the cochlea and superior semicircular canal. The posterior fossa dura is opened with a microblade (No. 59; Beaver Company), and the CSF is released, resulting in temporal lobe relaxation. At the fundus of the IAC, the vertical crest (Bill’s bar) and the labyrinthine facial nerve are exposed.

The dura of the IAC is incised along the posterior aspect, and the facial nerve is identified in the anterior portion of the IAC (Fig. 3.4). The superior vestibular nerve is divided at its lateral end. The tumor is separated from the facial nerve under high magnification, beginning at Bill’s bar and dissecting from medial to lateral (Fig. 3.5). The arachnoid is divided, the edge of the facial nerve identified, and the facial-vestibular anastomosis is sharply cut. This prevents excess traction on the facial nerve that can lead to neuropraxia. Intracapsular debulking can be performed, if needed, with microscissors and cup forceps. Again, tumor removal proceeds in the medial to lateral direction, here to prevent traction on the cochlear nerve and its blood supply as it enters the modiolus. The inferior vestibular nerve can be left in place if uninvolved in an attempt to preserve the labyrinthine artery; however partial vestibulopathy from a retained inferior vestibular nerve can result in persistent unsteadiness in some patients. For this reason, we recommend cutting the inferior vestibular nerve medial to the Scarpa’s ganglion, but not dissecting it at the fundus of the IAC (Fig. 3.6).

Once the tumor is removed, the tumor bed is irrigated and hemostasis is obtained. Papaverine-soaked Gelfoam is placed along the cochlear nerve to prevent vasospasm. Abdominal fat is used to close the defect in the IAC. The retractor is removed, and the temporal lobe is allowed to re-expand. The craniotomy flap is replaced with titanium mini-plates, the wound is closed with absorbable sutures in layers, and a mastoid-type pressure dressing is placed.

For the translabyrinthine approach, the operating room setup is identical to that for a standard mastoidectomy . The ipsilateral scalp is shaved four fingerbreadths above and behind the postauricular sulcus. The surgical site is prepped and draped in similar manner as the middle fossa approach. A hockey stick-shaped retroauricular skin incision that extends behind the mastoid tip is made with a No. 15 blade down to the temporalis fascia, hemostasis is obtained, and an anterior-based skin flap is elevated. A standard anterior-based periosteal flap is elevated with a Lempert elevator, and the mastoid cortex is exposed. Care must be taken not to violate the EAC skin when elevating the flap to prevent postoperative CSF otorrhea. Adson Cerebellar Retractors are placed at right angles to one another to retract the soft tissues. Temporalis muscle can be harvested at this time and placed on the back table to use for eustachian tube packing, if planned. A cortical mastoidectomy is performed with a high-speed drill, large cutting burrs, and suction irrigation. The dura should be exposed along the sigmoid sinus and tegmen at the sinodural angle, which is the deepest point of the dissection. The bone is removed 2 cm posterior to the sigmoid sinus to adequately expose the posterior fossa dura. A thin shell of bone is left over the sigmoid sinus (Bill’s island) to protect it from the shaft of the burr during the labyrinthectomy (Fig. 3.7). Some surgeons decompress the sigmoid sinus completely to facilitate retraction to improve exposure. The sinodural angle should be opened as far posteriorly as possible to facilitate a tangential view of the vestibule, which lies medial to the facial nerve [40]. We routinely open the facial recess, remove the incus, and pack the eustachian tube to prevent a route of egress of CSF. Alternatively, the facial recess bone and incus can be left intact. After tumor dissection, muscle can be packed around the incus in an effort to seal off the middle ear from the temporal bone defect and posterior fossa CSF flow [41]. The mastoid facial nerve is identified and followed down to the stylomastoid foramen.

A labyrinthectomy is performed with small (3–4 mm) cutting burrs (Fig. 3.8). The semicircular canals initially are skeletonized. The canals are then serially fenestrated and opened completely on a broad front, beginning with the horizontal semicircular canal. It is important to open on a broad front to provide continuous landmarks. The horizontal canal is opened down to its intersection with the posterior canal. The posterior canal is opened in a similar fashion up to its intersection with the superior canal (crus commons) superiorly and its ampullated end anterior-inferiorly, which marks the inferior border of the IAC. Caution must be taken to prevent damage to the mastoid segment of the facial nerve here. Bony removal proceeds inferiorly until the jugular bulb is identified at the same level as the IAC . The superior canal is opened along its entire path toward its ampulla, taking care not to violate the temporal lobe dura superiorly. The subarcuate artery is often encountered in the center of the arch of the superior canal, marking the superior border of the IAC [16]. All of the remaining bone between the vestibule and the jugular bulb is removed (Fig. 3.9).

Prior to opening the IAC , which begins deep to the vestibule and runs anteriorly away from the surgeon, its dura must be exposed in 270°. The cochlear aqueduct enters the posterior fossa in between the IAC and the jugular bulb and marks the inferior limit of bone removal . The bone is removed anterior to the cochlear aqueduct between the inferior IAC and jugular bulb to facilitate exposure to the inferior aspect of the tumor. Care is taken not to remove bone deep to the cochlear aqueduct to prevent injury to contents of the jugular foramen [42]. Bone superior to the IAC is removed last due to its location near the facial nerve in order to expose the superior aspect of the tumor (Fig. 3.10).

Prior to opening the dura, we vigorously irrigate the cavity with bacitracin solution to remove the bone dust. The posterior fossa dura is incised sharply over the midportion of the IAC with a microblade (No. 59; Beaver Company) and scissors. This incision is extended along the IAC and arches superiorly and inferiorly around the porus acusticus in a Y shape. For large tumors, the incision may need to be extended toward the sigmoid sinus [16]. Hemostasis is obtained with bipolar electrocautery. The arachnoid is opened with a sharp hook, allowing the egress of some CSF. At this point, only fenestrated suction tips should be used.

The facial nerve is again identified using stimulation and followed using a sharp right-angle hook, and Bill’s bar is palpated. The superior vestibular nerve and vestibulofacial fibers can be transected with this instrument. The inferior vestibular nerve is identified and cut. Once an adequate plane between the tumor and the facial nerve is developed, a blunt hook is used to continue the dissection. The motion of the dissection is from medial to lateral, to avoid traction on the facial nerve at its exit through the distal internal auditory canal (Fig. 3.11). The arachnoid enveloping the facial nerve is divided with a sharp right-angle hook. This is sometimes adequate to facilitate complete removal of small tumors (Fig. 3.12) [43]. If the tumor is large, the capsule can be incised, and the tumor can be debulked with either microsurgical instruments or an ultrasonic dissector. The tumor is followed to the brainstem, developing a plane with both blunt and sharp instrumentation. Cottonoids should be placed along the cerebellum and brainstem as they are exposed to protect the underlying structures. Intratumoral bleeding is controlled with bipolar cautery or topical hemostatics (as above), and only vessels that enter the tumor capsule are ligated.

Once the tumor is removed and hemostasis is complete, abdominal fat is harvested and cut into various-sized strips. The abdominal wound is closed with absorbable sutures and Steri-Strips, and a Penrose drain is left in place. The fat is soaked in bacitracin solution and packed tightly into the CPA, IAC, and mastoid cavity. Some surgeons advocate placing a titanium mesh or absorbable cranioplasty plate over the fat. The periosteal flap is reapproximated with 3–0 Vicryl sutures in a horizontal mattress fashion, ensuring a watertight closure. The subcutaneous tissues are reapproximated with buried interrupted 3-0 Vicryl sutures, and the skin is closed with either subcuticular absorbable sutures or a running locking 4-0 nylon suture. A standard mastoid-type pressure dressing is applied.