Subtemporal–Preauricular Approach to the Infratemporal Fossa

Abstract

Chordomas and chondrosarcomas of the skull base are pathologically and genetically distinct neoplasms that are often grouped together because of their similar radiologic, anatomical, and surgical features. Although rare tumors, compromising only about 0.15% of all intracranial tumors, they are, nonetheless, important pathologies because of their tendency to recur and to be locally invasive. Complete or near-complete resection followed by high-energy radiotherapy is used in the management of both lesions. An operative approach, in single- or multistage procedures, must be devised to maximize the probability of complete tumor removal, as this has been shown to have a dramatic impact on overall survival. In this chapter we discuss the techniques and indications for subtemporal–preauricular infratemporal fossa approaches.

Keywords

Chondrosarcoma, Chordoma, Infratemporal fossa, Microsurgery, Skull base tumors, Subtemporal–preauricular approach

Outline
Background 183
Application of the Approach 184
- Indications 184
- Limitations 184
- Advantages 186
- Disadvantages 186
Preoperative Evaluation and Planning 186
Operative Approach 187
- Pitfalls 189
Closure and Reconstruction 191
Case 1 193
Case 2 193
Case 3 193
References 202

Chordomas and chondrosarcomas of the skull base are pathologically and genetically distinct neoplasms that are often grouped together because of their similar radiologic, anatomical, and surgical features. Although rare tumors, compromising only about 0.15% of all intracranial tumors, they are, nonetheless, important pathologies because of the tendency to recur and to be locally invasive. Complete or near-complete resection followed by high-energy radiotherapy is used in the management of both lesions. An operative approach, in single- or multistage procedures, must be devised to maximize the probability of complete tumor removal, as this has been shown to have a dramatic impact on overall survival. In this chapter, we discuss the techniques and indications for subtemporal–preauricular infratemporal fossa approaches.

Background

Developed in 1987 by Sekhar and colleagues, the subtemporal–preauricular infratemporal fossa approach arose from modifications of the infratemporal fossa approach, first described in 1977 by Fisch, and of the middle fossa and transcochlear approaches, pioneered by House in 1963 and 1976, respectively. The subtemporal–preauricular infratemporal fossa approach is a primarily extradural route to the lateral and posterior skull base. It provides access to the anterolateral skull base with a shallow-angle exposure of the lateral midclivus ( Fig. 16.1A and B ).

The infratemporal fossa is bounded superiorly by the floor of the middle cranial fossa (squamous temporal bone and greater wing of the sphenoid), posteriorly by the cervical vertebrae, laterally by the mandibular ramus and condyle, and medially by the lateral pterygoid plate, pterygopalatine fossa, nasopharynx, and adjacent clivus. Surgical approaches to this region—as described by Fisch—achieve similar exposure, but necessitate disruption of the local anatomy and result in permanent conductive hearing loss (Fisch types A, B, and C) as well as facial nerve palsies due to cranial nerve (CN) VII transposition (Fisch types A and B). Translabyrinthine, transotic, and transcochlear approaches provide progressively more anterior exposure to the cerebellopontine angle, anterolateral brainstem, and clival area. These, however, cause ipsilateral hearing loss and, when the facial nerve is rerouted (transcochlear approach), at least temporary facial nerve palsy. The subtemporal–preauricular infratemporal fossa approach provides an anatomic exposure of the region, while avoiding the morbidity associated with facial nerve transposition and surgical disruption of the hearing apparatus.

We consider two primary variations of the subtemporal–preauricular infratemporal fossa approach: the subtemporal transzygomatic apical approach (STA) and the subtemporal–infratentorial approach (ST–ITA). The STA consists of a frontotemporal exposure combined with a zygomatic osteotomy (often combined with an orbital osteotomy) to provide access to the middle fossa, petrous apex, upper clivus, horizontal petrous internal carotid artery (ICA), and posterior cavernous sinus (CS) ( Fig. 16.2A–G ). The ST-ITA is an inferior extension of the STA into the neck and is used when the petroclival bone is involved inferior to the level of the horizontal segment of the petrous ICA. The ST-ITA provides additional exposure of the clivus to the level of the foramen magnum; the CS; the sphenoid, maxillary, and ethmoidal sinuses; the infratemporal fossa; and the retro- and parapharyngeal spaces and the orbit.

Application of the Approach

Indications

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The subtemporal–preauricular infratemporal approach is useful for lesions involving the middle clivus (from the petrous apex to the jugular foramen) and the petrous apex.
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It also provides access to the middle cranial fossa, infratemporal fossa, sphenoid area, parapharyngeal and retropharyngeal spaces, and the CS.
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Although best suited for extradural lesions, the subtemporal–preauricular infratemporal approach may also be used to remove tumors with intradural extension.
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Combination with an intradural subtemporal approach yields access to tumors ventral to the brainstem from the trigeminal root down to the hypoglossal foramina.

Limitations

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Tumor extension inferior to the level of the hypoglossal canal or across the midline may be difficult to remove by this approach.
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Any opening into the nasopharynx is important to recognize because it precludes a one-stage intra- and extradural procedure due to the risk of infection and the integrity of the vascular grafts.
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If the tumor has both intra- and extradural involvement, the extradural portion is performed first unless there is significant mass effect from the intradural portion.

Advantages

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Wide exposure is obtained through removal of bone and transposition of the petrous ICA rather than through brain retraction.
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The hearing apparatus is preserved by the preauricular route.
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Avoids trauma associated with transposition of extracranial segment of CN VII.
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Control of the ipsilateral petrous ICA and management of its injury is facilitated. Clival and petroclival neoplasms may involve the petrous ICA, and iatrogenic injury may occur during decompression or dissection. The subtemporal–preauricular infratemporal approach provides distal and proximal control of the petrous ICA and, if the incision is extended into the neck, of the upper cervical ICA.
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The proximity of external carotid artery (ECA) branches facilitates microvascular free flap transfer in reconstructing the skull base.
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The approach avoids transversing septic anatomical spaces.
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The exposure can be extended by dividing the mandibular nerve (V3) near the foramen ovale, elevating the temporal lobe, and tracing the petrous ICA to the CS. The artery may be completely mobilized, and the midclival and lower clival bones may be drilled away to reach the contralateral petrous ICA.
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This approach is readily combined with more anterior and posterior approaches to the cranial base.
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  Frontotemporal or subtemporal intradural approaches provide additional exposure of the upper clivus (from the anterior clinoid process to the petrous apex), tentorial notch, and CS.
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  Frontal transbasal approach provides extensive exposure of the anterior cranial base, midcranial base, clivus, and ipsilateral petrous and cavernous ICA.
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  Extreme lateral transcondylar and transjugular approach exposes tumors extending into the lower clivus (from the jugular bulb to the foramen magnum) and the foramen magnum.

Disadvantages

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The need for a wide operative field and exposure of vascular structures requires that the mandibular fossa be included in the osteotomy, the temporomandibular joint (TMJ) opened, and the condyle depressed or resected. Temporary malocclusion and trismus may result.
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Reversible conductive hearing loss results from sacrifice of the chorda tympani at the petrotympanic fissure and division of the eustachian tube (ET) during exposure of the petrous ICA.

Preoperative Evaluation and Planning

In addition to routine diagnostic radiography, axial and coronal fine-cut (1.5 mm) computed tomographic (CT) scanning to show any bone erosion by the tumor and delineate the tumor’s relationships to vascular, otologic, and petrous bone structures is indicated. Magnetic resonance imaging (MRI) with thin cuts is mandatory to define the nature and extent of the neoplasm. Constructive interference in steady state /fast imaging employing steady-state acquisition sequences may provide useful details of cisternal CN anatomy in cases in which there is significant intradural tumor extension. Angiography of both carotid and vertebral arteries in the neck and brain is strongly recommended and is of critical importance when the ICA is directly in contact with the tumor. When the ICA is encased in tumor, study of intracranial collaterals and communicating arteries and a balloon occlusion test determine the safety of ICA sacrifice/resection. Neurologic assessment and cerebral blood flow measurements (using xenon-enhanced CT scans) before and during carotid occlusion provide some indication of the patient’s tolerance of temporary carotid occlusion during surgery but do not predict the safety of permanent carotid occlusion. In cases in which the balloon occlusion test is not tolerated, the surgeon must plan and prepare for concomitant cerebral revascularization.

Intraoperative neurophysiological monitoring is used routinely and includes somatosensory evoked potentials, motor evoked potentials, electroencephalogram (EEG), brainstem auditory evoked potentials, and CN stimulation and monitoring. Anesthesia is induced and maintained with short-acting intravenous and gaseous agents, while avoiding prolonged neuromuscular paralytics to enable actuate neurophysiologic monitoring. Mannitol and intravenous dexamethasone are administered, and a lumbar cerebrospinal fluid (CSF) drain or ventriculostomy may be placed to enhance brain relaxation. Normal blood pressure is maintained throughout the procedure. If the ICA is temporarily occluded, the anesthetic level should be deepened with neuroprotective agents to induce burst suppression on EEG and the mean arterial pressure should be raised to 20% above the patient’s baseline.

Operative Approach

The patient is placed supine in pins, the head is turned 60 degrees away, and the neck is fixed in slight extension with the malar eminence at the highest point in the field. Intraoperative neuronavigation is registered once the patient is secured after positioning. The head, neck, any sites for the extraction of fat grafts and fascia, and medial thigh or the anterior aspect of the forearm are also prepped in the event that a vascular graft is needed. The preauricular limb of the incision extends just below the zygomatic process for the STA. The remainder of the incision is passed forward along the superior temporal line or is taken bicoronally behind the hairline. The scalp flap is mobilized anteriorly, taking care to preserve a pericranial flap if desired. Either a subfascial or an interfascial dissection is performed over the temporalis muscle to exposure the lateral orbital rim and zygoma.

For the ST-ITA exposure, the incision is extended further inferiorly, reaching the lower border of the ear lobule. At the junction of the tragus and helix the incision is angled around the helix of the ear to form a 90-degree indentation. This provides a better cosmetic result. The superficial temporal artery and vein, the upper branches of the facial nerve, and the parotid gland tissues are elevated from the masseteric fascia in a “reverse degloving procedure” ( Fig. 16.3 ) which prevents excess traction on the facial nerve when the mandible is displaced. Soft tissues below the zygoma are mobilized anteriorly with the scalp flap along the plane of the masseteric fascia. This provides adequate additional inferior exposure in the infratemporal region and avoids the need to dissect the facial nerve. The cervical ICA is exposed for proximal control in older patients and in cases in which the tumor may encase the ICA. The temporalis muscle is detached in a subperiosteal plane, elevated from the underlying bone, and reflected anteroinferiorly. The masseter muscle is dissected free from the inferior border of the zygoma.