Surgical Neurotology

Updated: Jan 17, 2014
  • Author: Rodney C Diaz, MD; Chief Editor: Kim J Burchiel, MD, FACS  more...
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Overview

Background

The neurotology/neurosurgery team has at its disposal numerous approaches for traversing the lateral skull base and accessing the intracranial vault. [1] The discussion of approaches is divided, somewhat arbitrarily, into 3 general categories: transtemporal approaches, suboccipital approaches, and subtemporal approaches.

The transtemporal approaches are grouped to encompass techniques in which the temporal bone is the primary target through which dissection and intracranial access are achieved. The suboccipital approaches group those procedures where variations in suboccipital craniotomies provide access to the posterior fossa. The subtemporal approaches are those procedures where access to varying regions of the middle or posterior fossae are achieved caudal to the temporal lobe.

Finally, combined middle fossa- posterior fossa approaches are discussed. As will be readily demonstrated, many approaches combine elements of subtemporal, suboccipital, and transtemporal vectors and can be considered in multiple ways.

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Indications

Lateral Temporal Bone Resection

The lateral temporal bone resection is a procedure that can be performed for direct therapeutic effect in resecting tumors of the external auditory canal. Depending on the size, location, invasion, and nature of tumor, the lateral temporal bone resection can be combined with partial or total auriculectomy, parotidectomy and / or neck dissections to provide appropriate complete surgical extirpation of neoplastic disease. This resection is performed when the tumor is involving the external auditory canal and extending to but not beyond the tympanic membrane. In cases in which the tumor has extended beyond the bony confines of the external auditory canal or through the tympanic membrane and is involving the mesotympanum or mastoid air cells, a subtotal or total temporal bone resection is indicated.

In addition to its use in the definitive treatment of neoplastic disease in the external auditory canal, the lateral temporal bone resection serves as the basis for lateral temporal bone resection involving other transtemporal approaches to the skull base, including the transotic, transcochlear, and infratemporal fossa type A approaches, which are described later in the section.

Subtotal Temporal Bone Resection

When tumor has extended into the middle ear cleft, a subtotal temporal bone dissection is warranted. However, recurrence rates and long-term mortality are significantly increased when tumors have breached this plane and entered the medial temporal bone .

Total Temporal Bone Resection

When neoplastic disease has invaded the medial temporal bone and resection beyond the otic capsule is necessary to achieve total tumor resection, a total temporal bone resection is performed. Despite the aggressive nature of the procedure, long-term and disease-free survival following this resection is dismally poor.

When the petrous carotid artery is resected, the procedure is sometimes termed a radical temporal bone resection. Involvement of the intrapetrous carotid artery by neoplastic disease portends dismal short-term survival.

Modified Translabyrinthine Approach

The modified translabyrinthine technique can be considered in a similar light as the posterior semicircular canal occlusion procedure for intractable benign paroxysmal positional vertigo, but the modified translabyrinthine approach involves occlusion of all 3 semicircular canals instead of just 1. [new para]Occlusion of the posterior semicircular canal for intractable vertigo allows for excellent postoperative hearing outcomes, with the vast majority of surgical recipients maintaining normal hearing. [5] In contrast, occlusion of all 3 canals and skeletonization of the vestibule, in conjunction with intracanalicular tumor dissection performed in the modified translabyrinthine approach,* yields postoperative preservation of serviceable hearing in at best 40-50% of patients. [4, 6]

Retrolabyrinthine Approach

Occasionally, a small tumor of the cerebellopontine angle has little or no extension into the internal auditory canal, or a tumor of the mastoid has extended through the posterior fossa dural plate into the cerebellopontine angle. In such cases in which transmastoid access to the cerebellopontine angle can be significantly restricted without impeding tumor removal, a strictly retrolabyrinthine dissection can be performed.

Despite the potential to preserve hearing, the retrolabyrinthine approach has limited application due to its extremely narrow window of intracranial exposure.

Transotic Approach

On the opposite end of the spectrum, the transotic and transcochlear approaches expand rather than restrict the limits of dissection. [7] In cases in which the tumor being accessed has significant anterior petrous apex or cerebellopontine angle extension, the translabyrinthine approach may be extended anteriorly.

Transcochlear Approach

When wide anterior petrous apex exposure is necessary, the facial nerve can be removed from its entire course within the bony fallopian canal and transposed posteriorly. This anterior petrous apex exposure is termed the transcochlear approach.

Infratemporal Fossa Type A Approach

When wide exposure along the posterior petrous apex and jugular bulb are required, the infratemporal fossa type A approach is used. This approach is commonly used when resecting tumors of the jugular bulb, such as glomus jugulare tumors.

Fallopian Bridge Technique

A significant morbidity to the infratemporal fossa A approach is the necessity for facial nerve transposition. Facial nerve transposition causes a complete facial paralysis acutely. Long-term facial function rarely exceeds a House Brackmann grade 3, as long-term facial synkinesis as a result of bulk movement of the nerve almost always occurs.

An alternative approach to achieving lateral exposure of the jugular bulb is to perform the so-called “fallopian bridge” technique.

Transjugular Approach

The transjugular approach is used to expose the jugular bulb, jugular foramen, and cerebellopontine angle for resection of combined extracranial - intracranial jugular foramen tumors. [8]

Retrosigmoid Approach

This approach is useful for large tumors over 3-4 cm or with significant inferior or superior extension* and tumors in which the jugular bulb is high, constricting inferior access to the cerebellopontine angle through a translabyrinthine craniotomy. The retrosigmoid approach is also used when a hearing conservation approach to tumor removal is desired, particularly in tumors with significant cisternal extension not amenable to middle fossa approach. The retrosigmoid approach is described in detail in the Medscape Reference topic Acoustic Neuroma.

Far Lateral Approach/Transcondylar Approach

The transcondylar approach offers extended access to the posterior fossa from the tentorium to the cervicomedullary junction.

Extreme Lateral Approach

The transcondylar approach can be extended to encompass the lateral sinus, jugular bulb, and jugular foramen. This lateral extension provides access to the ventral cervicomedullary junction* or to the jugular foramen itself. [10] The approach is often combined with a retrolabyrinthine extension superiorly into the mastoid cavity, which is used when the target of dissection is the jugular bulb and jugular foramen as opposed to the ventral cervicomedullary junction. This approach is termed the extreme lateral approach.

Postauricular Subtemporal Approach/Posterior Petrosectomy/Middle Fossa Approach

The middle fossa approach is applicable for tumors that are intracanalicular. The great advantage to the middle fossa approach is the ability to visualize the entire internal auditory canal from fundus to porus and resect tumors completely with good hope for hearing preservation. However, this approach, without modification, does not provide adequate posterior fossa exposure and hence is not appropriate for tumors extending more than 3-5 mm beyond the porus acusticus. The middle fossa approach is described in detail in the Medscape Reference topic Acoustic Neuroma.

Infratemporal Fossa Type C Approach

The infratemporal fossa type C approach is used for tumors along the anteriormost extent of the petrous bone and clivus but with more significant extension subcranially within the infratemporal fossa and pterygomaxillary fissure.

Extended Middle Fossa Approach

When additional exposure is needed within the cerebellopontine angle through a subtemporal craniotomy, the middle fossa or postauricular subtemporal approach can be combined with the preauricular subtemporal approach to provide such exposure. This extended middle fossa approach provides adequate access to the cerebellopontine angle to allow for tumor removal for intracanalicular tumors with significant cisternal component. [13] This approach is of limited use for tumors with significant brainstem compression, however.

Combined Middle Fossa-Posterior Fossa Approaches

Large intracranial tumors that traverse both the middle and posterior fossae often cannot be fully accessed by a subtemporal or suboccipital approach alone. Combining subtemporal and suboccipital approaches allows for wide exposure of the prepontine cistern, clivus, and petroclival junction, where such tumors present.

Subtemporal-Translabyrinthine Petrosal Approach

The subtemporal- translabyrinthine petrosal craniotomy provides even greater anterior exposure, not just to the petroclival region, but a complete view of the internal auditory canal as well. The advantage of greater anterior exposure is tempered by the postoperative anacusis induced through this approach. A variation of this approach, the transcrusal approach, attempts to maintain neurosensory hearing function by limiting translabyrinthine resection to just the superior and posterior semicircular canals.

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Contraindications

Anterior Transpetrosal Approach-Total Petrosectomy Approach

This temporal bone dissection, under either name, is not commonly performed. The entire anterior petrous apex does not need to be resected to visualize the clivus and prepontine cistern: this can be partially accessed with a subtemporal- retrolabyrinthine approach or completely accessed with a subtemporal- transcochlear approach without brain retraction. Total petrosectomy for advanced, invasive malignant disease causes significant perioperative morbidity and possibly mortality yet will do little to improve prognosis.

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