ADVANTAGES OF TRANSCOCHLEAR APPROACH

This approach requires no cerebellar or temporal lobe retraction. Exposure and dissection of the petrous apex and clivus allows excellent exposure of the midline and complete removal of the tumor, its base of implantation, and its blood supply. This is of particular importance in meningiomas.^10,11

Careful handling and constant monitoring of the facial nerve during rerouting prevent injury to the intratemporal portion of the nerve. Cholesteatomas tend to wrap themselves around it. If the facial nerve is lost during tumor removal, we recommend immediate repair by end-to-end anastomosis or nerve graft interposition.

DISADVANTAGES OF TRANSCOCHLEAR APPROACH

The main disadvantages of this approach are sacrifice of residual hearing in the operated ear and risk of temporary facial palsy. This technique is indicated when no serviceable hearing exists in the involved ear, or when the tumor is too far anterior for the extended middle fossa craniotomy approach or transpetrous approach. With the use of continuous facial nerve monitoring, the incidence of permanent facial nerve paralysis is low.

PATIENT EVALUATION AND PREOPERATIVE COUNSELING

Individuals with tumors that require transcochlear surgery may have minimal symptoms, with tumors that can be quite large at the time of diagnosis.^1,12 Petrous apex epidermoids manifest with unilateral hearing loss and tinnitus in 80% of the cases. Facial twitch is also common. Imbalance, ataxia, and parietal or vertex headaches may be the only complaints in 20% of patients.¹³ Patients with meningiomas and intradural epidermoids may be nearly symptom-free until they present with CN V findings and signs of increased intracranial pressure.^14,15 There is a high rate of jugular foramen syndrome in patients with meningiomas.¹ Seizures, dysarthria, and late signs of dementia from hydrocephalus were common presenting symptoms in the past.¹³ Hearing and vestibular functions are frequently normal, and acoustic reflex decay or abnormal auditory brainstem response audiometric results may be the only anomalies.¹

Imaging using high-resolution computed tomography (CT) with contrast enhancement, magnetic resonance imaging (MRI), and magnetic resonance angiography (MRA) is essential for diagnosis and surgical planning.¹⁶ Petrous apex and intradural epidermoids are expansile, spherical, or oval lesions, with scalloped bone edges on CT. They are isodense to cerebrospinal fluid on CT, with capsular enhancement. On MRI, they are hypointense on T1-weighted images and hyperintense on T2-weighted images. Meningiomas enhance with contrast on MRI, and manifest with a “dural tail.” Evaluation of blood supply of some tumors may also require MRA. In tumors surrounding or invading the intrapetrous carotid artery, patency of the circle of Willis is accessed, and carotid residual pressure is measured; preoperative balloon occlusion of the carotid artery and selective embolization are performed 1 day before surgery. Radioisotope, xenon, or positron emission tomography studies are used to assess cerebral perfusion during occlusion studies.

The natural history of petrous apex epidermoids is that they grow slowly and may produce cranial neuropathies; they may also become infected. Treatment is difficult when infection occurs, and meningitis, sepsis, and death may result. Intracranial epidermoids spread through the cisterns and subarachnoid planes to neighboring regions, including the opposite CPA. Petrous ridge meningiomas grow and are space-occupying lesions that increase intracranial pressure. After surgery, intracranial pressure is reduced, and cranial nerve symptoms tend to improve. Risks and complications in the immediate postoperative period include transient vertigo; complete hearing loss; temporary CN VII, IX, X, XI, and XII paresis; infection; bleeding; swallowing difficulties; aspiration pneumonia; cerebrovascular accidents; and, rarely, death.

SURGICAL ANATOMY

Intracranial structures that may be exposed by the transcochlear approach include the entire lateral aspect of the pons and upper medulla, CN V through XI, and the midbasilar artery. Posterior fossa exposure is extensive except inferiorly, where it is limited in the area of the jugular foramen and foramen magnum. The degree to which the neural compartment of the jugular foramen is visible depends on the height of the jugular bulb. Modifications to the transcochlear approach permit identification of the anterior aspect of the pons and both sixth cranial nerves, and improved identification of the basilar artery and vertebrobasilar junction.

SURGICAL TECHNIQUE

A wide mastoidectomy and labyrinthectomy are performed, exposing the IAC. When first described by House and Hitselberger in 1976,³ the tympanic ring was not removed, and only the facial recess was opened to permit anterior exposure. Brackmann, after Fisch, modified the approach by removing the entire tympanic ring, malleus, incus and stapes, and blind-sac closing the EAC.^17,18

The facial nerve is completely skeletonized, with transection of the greater superficial petrosal and chorda tympani nerves, and is rerouted posteriorly out of the fallopian canal. The cochlea and the fallopian canal are completely drilled out, and the internal carotid artery is skeletonized. A large triangular window is created into the skull base. Its superior boundary is the superior petrosal sinus; inferiorly, it extends below and medial to the inferior petrosal sinus into the clivus. Anteriorly lies the region of the intrapetrous internal carotid artery, and the apex of the triangle is just beneath Meckel’s cave. When the dura is opened, this window gives excellent direct access to the midline without need of any retraction (Fig. 52-1). After tumor removal, the dura is reapproximated with dural silk, the eustachian tube is packed with absorbable knitted fabric (Surgicel) and muscle, and abdominal fat is used to fill the dura and mastoidectomy defects and to cushion the facial nerve.

FIGURE 52-1 Transcochlear approach. Exposure obtained at skull base at completion of approach. Ba, basilar artery; EAC, external auditory canal; ICA, internal carotid artery; SPS, superior petrosal sinus; SS, sigmoid sinus; T, tumor.

Mastoidectomy

An extended mastoidectomy (Fig. 52-2) is carried out with microsurgical cutting and diamond burrs and continuous suction-irrigation. Bone removal is started along two lines: one along the linea temporalis and another tangential to the EAC. The mastoid antrum is opened, and the lateral semicircular canal is identified. The lateral semicircular canal is the most reliable landmark in the temporal bone, and allows the dissection to proceed toward delineating the vertical fallopian canal and the osseous labyrinth.

FIGURE 52-2 Mastoidectomy. There is wide exposure of posterior and middle fossa dura, with identification of bony labyrinth and skeletonization of sigmoid sinus. Bill’s island (BI) is preserved initially, then removed after internal auditory canal skeletonization. EAC, external auditory canal; MFD, middle fossa dura; PCW, posterior canal wall; PFD, posterior fossa dura; FN, facial nerve.

The opening of the mastoid cavity must be as large as possible and is extended posterior to the sigmoid sinus, exposing 1 to 2 cm of suboccipital dura. The larger the tumor, the further back the posterior fossa dura is exposed, to a maximum of 2 to 3 cm.

Mastoid emissary veins are dissected, and bleeding is controlled using bipolar cautery and Surgicel packing. Removal of bone over the sigmoid sinus is performed with diamond burrs, and an island of bone (Bill’s island) may be left over the dome of the sinus initially. This eggshell of bone protects the sinus from being injured by the shaft of the burr. Bone is removed from the sinodural angle along the superior petrosal sinus. The mastoid air cells are exenterated from the sinodural angle, skeletonizing the dura of the posterior and the middle fossae.

Labyrinthectomy and Skeletonization of Internal Auditory Canal

Dissection of the perilabyrinthine cells down to the lateral semicircular canal is completed (Fig. 52-3). The facial nerve is identified in its vertical portion between the nonampullated end of the lateral semicircular canal and the stylomastoid foramen. At this stage, exposing the perineurium of the nerve is unnecessary, but it should be clearly and unmistakably identified in its vertical course.

FIGURE 52-3 Exposure of internal auditory canal, skeletonization of facial nerve from internal auditory canal to stylomastoid foramen, and extended facial recess. Labyrinthectomy has been completed.

The lateral semicircular canal is fenestrated superiorly, and the membranous portion is identified and followed anteriorly to its ampullated end and posteriorly to the posterior semicircular canal. All three membranous and bony semicircular canals are removed, and the saccule and utricle in the vestibule are identified and removed.

The dissection proceeds along the sinodural angle and the superior petrosal sinus. The dura of the posterior fossa is exposed anteriorly. The cells over the jugular bulb are removed, skeletonizing it, and the cochlear aqueduct is removed. To obtain a better control of the lower cranial nerves and the vertebrobasilar junction, the jugular bulb is completely exposed and, if needed, compressed. The IAC is skeletonized, beginning inferiorly and then around the porus acusticus. The falciform crest (transverse) and vertical crest (Bill’s bar) are used as identifying landmarks for the superior and inferior vestibular nerves and the facial nerve. The bone of Bill’s island over the sigmoid sinus is removed. The superior and inferior vestibular and cochlear nerves are excised.

Facial Nerve Rerouting (Figs. 52-4 and 52-5)

After removal of the incus, if the bony EAC was not removed, an extended facial recess opening is created. The facial nerve is completely skeletonized from the IAC to the stylomastoid foramen, including the geniculate ganglion, with diamond burrs. An area comprising 180 degrees of the bony fallopian canal is uncovered. The greater superficial petrosal nerve is cut at its origin from the geniculate ganglion. The facial nerve is reflected posteriorly out of the fallopian canal with care taken to avoid traction or bending on the nerve, especially near the geniculate ganglion, where the nerve is reduced in size and forms an acute angle, and near the mastoid genu, which is the site of several branches to the stapedius muscle. Care is also taken to avoid kinking of the nerve near the stylomastoid foramen when reflecting it posteriorly. The facial nerve is protected at all times and kept wet. The IAC dura is preserved, and CN VII and VIII, with all the protecting dura, are rerouted posteriorly.

FIGURE 52-4 Bone over facial nerve is removed. At this point, the greater superficial petrosal nerve is sectioned. GG, geniculate ganglion; IAC, internal auditory canal; MFD, middle fossa dura; PDF, posterior fossa dura; SS, sigmoid sinus.

FIGURE 52-5 Location of facial nerve after it is completely reflected posteriorly out of bony fallopian canal. FC, fallopian canal; Fn, facial nerve; JB, jugular bulb; MFD, middle fossa dura; PFD, posterior fossa dura; SDA, sinodural angle; SS, sigmoid sinus.

Transcochlear Drill-out (Fig. 52-6)

The fallopian canal and the ossicles have been removed, and the promontory is now exposed. Starting with the basal coil, the cochlea is completely drilled out. Bone removal is carried forward around the internal carotid artery, and inferiorly the bone removal extends to the inferior petrosal sinus and jugular bulb. Superiorly, the superior petrosal sinus is followed to Meckel’s cave. Medially, bone removal extends to the clivus. At this stage, a large triangular window, covered by dura, has been created into the midline of the skull base. Its boundaries are the superior petrosal sinus superiorly; below and medial to the inferior petrosal sinus into the clivus inferiorly; the region of the internal carotid artery anteriorly; and the lateral clivus medially. The apex of the triangle is just beneath Meckel’s cave.

FIGURE 52-6 Cochlear drill-out. Co, cochlea; Fn, facial nerve; ICA, internal carotid artery; JB, jugular bulb; MFD, middle fossa dura; PFD, posterior fossa dura; SS, sigmoid sinus.

Tumor Removal (Fig. 52-7)

With meningiomas, arterial feeder vessels from the internal carotid artery are encountered and eliminated during the approach. The diamond burr is used to excise these vessels and the base of implantation at the petroclival area. The dura is opened anterior to the IAC, and the opening is extended as far forward as necessary for complete tumor exposure. The dural opening extends from the superior petrosal sinus superiorly to the inferior petrosal sinus inferiorly. CN V, VII, and VIII are identified.

FIGURE 52-7 Tumor removal. Tumor is removed with a House-Urban rotatory dissector or with an ultrasonic aspirator. BA, basilar artery; BS, brainstem; Fn, facial nerve; ICA, internal carotid artery; SS, sigmoid sinus.

The facial nerve is kept on the posterior surface of the tumor. The junction of the intracranial portion of the facial nerve and the skeletonized intratemporal portion is now identified.

The nerve is protected and kept moist.

The tumor pseudocapsule is opened, and the center of the main mass of the tumor is removed with the House-Urban rotatory dissector or with an ultrasonic aspirator. As the dissection proceeds forward and medially, the basilar artery and CN VI are identified anterosuperiorly. The vertebral arteries appear posteroinferiorly. The tumor is removed from these vessels and their major tributaries under direct vision. In tumors extending across the midline, the basilar artery and its major branches can be dissected posteriorly off the tumor capsule. When the lesion is removed in this fashion, the cranial nerves and the IAC in the opposite CPA come into view. No brain retractors are needed to allow for this exposure.

For dumbbell-shaped tumors, the tentorium can be opened to excise the part of the tumor that is lying in the middle fossa. Care is taken not to injure the vein of Labbé posteriorly or CN IV at the edge of the tentorium. Figures 52-8 to 52-12 illustrate the transcochlear approach with removal of the tympanic bone and blind closure of the EAC, which is done when further anterior exposure is necessary.

FIGURE 52-8 Increased anterior exposure obtained with removal of bony external auditory canal. E, exposure.

FIGURE 52-9 Mastoidectomy. Meatus is closed in three layers; skin, tympanic membrane, malleus, and incus are removed; and bony external auditory canal is drilled out. BI, Bill’s island; FC, fallopian canal; JB, jugular bulb; PFD, posterior fossa dura.

FIGURE 52-10 A and B, Cochlea and adjacent part of petrous apex (PA) are drilled away. Internal carotid artery (ICA) is exposed at anterior limit of dissection. Co, cochlea; Fn, facial nerve; JB, jugular bulb; SS, sigmoid sinus.

FIGURE 52-11 Final dural exposure and outlining of dural incision. Fn, facial nerve; ICA, internal carotid artery; JB, jugular bulb; MFD, middle fossa dura; PFD, posterior fossa dura; SS, sigmoid sinus.

FIGURE 52-12 Tumor removal and structures seen at skull base at completion of approach. Basilar artery (BA) and CN VI are seen. ICA, internal carotid artery; JB, jugular bulb; SPS, superior petrosal sinus; SS, sigmoid sinus; T, tumor.

POSTOPERATIVE CARE

The patient is observed in the intensive care unit for 24 hours after surgery and remains in the hospital for 4 to 5 days. Steroids are continued for 48 hours. Antibiotics are routinely used after the perioperative period. With early mobilization and ambulation, thromboembolism is avoided, and there is a speedy return of balance.

RESULTS

In 1982, De la Cruz¹ reviewed the results of 16 patients in whom the transcochlear approach was used. A combination transcochlear/middle fossa approach was used in the three cases involving dumbbell-shaped tumors in the posterior and middle cranial fossae. Total tumor removal was possible in 13 of the 16 patients. Each of the other three patients had had surgery elsewhere and presented with large recurrent meningiomas and extensive neurologic deficits preoperatively. During the transcochlear approach, scraps of tumor were left behind on the vertebral artery in two of these cases. None of these patients had tumor recurrence. Four patients had facial paresis or twitch preoperatively; of the other 12, 4 had permanent facial paralysis because of tumor involvement of the nerve, and 7 had temporary paresis with good recovery of facial function. This paresis was attributed primarily to removal of blood supply to the nerve, and these patients were operated on before facial nerve monitoring was available. Two deaths occurred in this series. One patient had bleeding from the vertebral artery 1 week postoperatively, requiring clipping of the vessel, with subsequent infarction of the brainstem; the other patient was diabetic and died 1 month postoperatively because of gram-negative shock from pyelonephritis. He was one of the patients reported as having a “permanent” facial paralysis. Autopsy revealed no evidence of residual tumor on the facial nerve or elsewhere.

In 1989, Yamakawa and colleagues¹⁵ published their results with the suboccipital approach, reporting subtotal tumor removal in 17 of 29 patients with intracranial epidermoids and tumor recurrence in 7 patients. One of 14 patients with CPA tumors had postoperative CN VII paralysis, 6 had CN VI palsy, 4 had dysphagia, and 2 had hearing loss. The report by Yasargil and associates¹⁹ published in the same year analyzed results in 43 patients; 35 had epidermoid tumors, whereas others had intracranial dermoid tumors. There were no recurrences. Aseptic meningitis and transient cranial nerve palsies were the most common complications.

In 2001, Angeli and coworkers²⁰ reviewed 24 cases operated on between 1985-1995 at the House Ear Clinic using the transcochlear approach or 1 of its modifications. In 1 case, a modified transotic approach was used (small melanoma); in 2 other cases, the transcochlear approach was extended inferiorly with an infratemporal and upper neck dissection (1 glomus and 1 meningioma). Most of the tumors (16 of 24) were meningiomas. The other tumors included 4 cholesteatomas, 2 melanomas, 1 glomus, and 1 ependymoma. The EAC was closed in 12 patients. Complete removal was achieved in 82% of tumors (average follow-up time 36 months). In 2 cases (8%), it was elected intraoperatively to do a subtotal tumor resection owing to excessive blood loss (intracranial glomus jugulare tumor) in 1 and unresectability (melanoma invading the brainstem) in 1. Most patients had some degree of facial nerve dysfunction immediately after surgery, and 12 of 20 patients subsequently improved to House-Brackmann grade III or better. A significant incidence of temporary facial weakness was expected as a result of posterior facial nerve transposition. 59% of patients had permanent neurologic sequelae because of either the surgery or their disease. The most common neurologic deficit was diplopia (27%). Other complications included dysphagia, facial numbness, unsteadiness, hoarseness, hemiparesis, and dysarthria.

In 2004, Gonzalez and associates²¹ reported 32 patients with 34 anterior inferior cerebellar artery aneurysms. Surgical approaches included retrosigmoid, transcochlear, translabyrinthine, and orbitozygomatic. The transcochlear approach was used in 4 patients; 1 patient had small bilateral aneurysms that were approached, with good results, from the same side by taking advantage of the wide corridor obtained with a transcochlear approach. Complications reported were involvement of CN VI, VII, and VIII, and CSF leak.

Siwanuwatn and coworkers²² quantitatively assessed the working areas and angles of attack associated with retrosigmoid, combined petrosal, and transcochlear craniotomies, using silicone-injected cadaveric heads. They reported that the transcochlear approach provided significantly greater working areas at the petroclivus and brainstem than the combined petrosal and retrosigmoid approaches (P < .001). The horizontal and vertical angles of attack achieved using the transcochlear approach were wider than the angles of the combined petrosal and retrosigmoid at the Dorello canal and the origin of the anterior inferior cerebellar artery (P < .001). They concluded that the transcochlear approach provides the widest corridor, improving the working area and angle of attack to both areas.

In 2006, Leonetti and colleagues²⁴ reported 29 patients with large meningiomas of the CPA surgically treated through a combined retrosigmoid/transpetrosal/transcochlear approach. Total tumor removal was achieved in 19 of 29 (67%) of the patients, and the facial nerve was anatomically preserved in 26 of 29 (89%) of the cases. Cerebrospinal fluid leakage was seen in 3.5% of the patients, and additional transient cranial nerve deficits were noted in 14% of the cases, but no significant neurologic sequelae occurred. Of the 10 patients with residual tumor, 6 have been stable without growth, 2 were treated with reoperation for regrowth of disease, and 2 were controlled with localized radiotherapy. These investigators concluded that this combined lateral transtemporal approach provided wide exposure to the CPA and optimized the surgical extirpation of the 29 meningiomas presented in their series.

COMPLICATIONS AND THEIR MANAGEMENT

Temporary facial nerve paresis is the most common complication. If facial paresis occurs, prompt eye care is essential; adequate lubrication with drops, nighttime ointments, and a moisture shield prevent corneal complications. Unless the facial nerve has been severed, surgical intervention for facial reanimation is not indicated. The best approach in individuals with even complete paralysis after transcochlear surgery, if the facial nerve is anatomically intact, is eye care that includes soft lenses, spring and gold weights, sometimes canthoplasty, and “watchful waiting” because most of these patients recover to an acceptable grade of facial function within the first year after surgery.

Other cranial nerve palsies may occur and should be addressed individually. The neurotologist must attain a good working relationship not only with a neurosurgeon, but also with an ophthalmologist and a laryngologist to help in the management of these cranial nerve deficits.

Intracranial bleeding is controlled at the time of surgery. Close observation of the patient in the intensive care unit for the initial 24 hours postoperatively allows early recognition of delayed postoperative intracranial hemorrhage. In these cases, treatment consists of immediate reopening of the surgical wound and removal of the fat in the intensive care unit while the operating room is being prepared, and then operative evacuation of the hematoma and control of the bleeding site or sites.

Meningitis may occur after complete excision of intracranial epidermoids, and the incidence increases when the tumor capsule is left in place.^19,24

Meningitis may be fatal if it is infectious and requires early, aggressive antibiotic therapy. More commonly, however, it is a chemical aseptic meningitis, and the patient is treated with dexamethasone.

Postoperative pain is not as severe as that seen with the suboccipital approach and is managed adequately with analgesics. With this approach, tumor recurrence is rare when all visible tumor has been removed. Patients with recurrences do not present typically and may have vague complaints of unsteadiness or trigeminal symptoms several years after the initial resection.¹ Annual follow-up with gadolinium-enhanced and fat-suppression MRI is necessary. In cases of suspected tumor regrowth or recurrence, complete re-evaluation is performed, and removal of the recurrent tumor is advised. Gamma knife stereotactic radiosurgery and stereotactic radiotherapy are also treatment options for residual or recurrent meningiomas.²⁶

SUMMARY

Access to midline intradural lesions, intradural petroclival tumors, and CPA tumors arising anterior to the IAC has traditionally been difficult. With the transcochlear approach, the facial nerve is mobilized, the cochlea is removed, and the petrous apex is dissected around the internal carotid artery, allowing direct exposure of these lesions and of midline and contralateral CPA structures, without using retraction. Total removal of the tumor and its base and blood supply is possible with this approach. The transcochlear approach is recommended for these lesions in patients with poor hearing. Its safety and efficacy encourage its use.