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Approaches to the Temporal Bone: Basic Principles


In this chapter we will introduce the anatomy and some key steps for the three most relevant approaches to the temporal bone for the neurosurgeon: the subtemporal or middle fossa approach, the translabyrinthine and the transcochlear approach.

Middle Fossa or Subtemporal Approach

  • Good for hearing preservation, as it allows direct access to the IAC without the need for a labyrinthectomy. Also, the risk of CSF leaks decreases in this approach.

  • Anterior and posterior petrosectomies can provide additional working space and versatility to this approach.

  • Temporal lobe retraction is necessary most of the time, increasing the risk of damage to the vein of Labbé and of temporal lobe ischemia.

  • Provides limited access to the CPA.

Indications

  • Small tumors with less than 1 cm cerebellopontine extension.

  • Petroclival tumors extending to the CPA.

  • Petrous apex granulomas.

Contraindications

  • Tumors arising from the CPA.

Surgical Procedure

Patient Position ( Figure 35.1 )

  • The patient can be placed in the supine position.

  • Placement of a shoulder roll under the ipsilateral shoulder is recommended.

  • The head can be fixed with a three-point Mayfield headholder, angled 90° from the vertical plane and tilted approximately 20° toward the floor, placing the zygoma at the highest point in the field.

  • This position allows for the temporal lobe to fall with gravity and provides a direct visualization of the tentorium.

  • Adequate space between the chin and the clavicle is recommended to avoid contralateral jugular compression.

  • Patient registration for navigation is recommended at this stage to assist with the planning of the surgical trajectory.

Figure 35.1, The patient is positioned supine with a shoulder roll under the ipsilateral shoulder. After pinning, the head is angled 90° from the vertical plane and then tilted approximately 20° toward the floor such that the zygoma is the highest point in the field. This position allows for the temporal lobe to fall with gravity in addition to providing a line of view flush with the tentorium.

Skin Incision

  • A horseshoe incision is recommended ( Figure 35.2 ).

    Figure 35.2, Skin mark for horseshoe incision, starting anteriorly at the zygomatic root and extending superiorly towards the superior temporal line, turning posteriorly and finishing at the asterion area.

  • Start anteriorly at the zygomatic root and extend it superiorly towards the superior temporal line, turning posteriorly and finishing at the asterion.

  • The incision is carried down to the temporalis fascia. Preservation of the superficial temporal artery and its branches is recommended.

Craniotomy

  • Burr holes are performed at the squamosal temporal bone, zygomatic root, superior temporal line, asterion and superior/posterior to the insertion of the vein of Labbé into the transverse sinus.

  • A bone flap is created with a craniotome. We recommend to drill the bone as close to the floor of the middle cranial fossa as possible, for a better surgical corridor. Additionally, the inferior part of the craniotomy can be undermined to allow a good exposure of the petrosal portion of the temporal bone. Approximately two-thirds of the craniotomy is placed anterior to the external auditory meatus ( Figure 35.3 ).

    Figure 35.3, The usual location for the burr holes for the subtemporal craniotomy (A) in the squamosal temporal bone at the zygomatic root, (B) superior temporal line, (C) asterion (at the level of the middle fossa) and (D) superiorly (behind the area of insertion of the vein of Labbé into the transverse sinus).

Dural Opening

  • A U-shaped dural incision, with an inferior base, is made. Caution is advised to avoid the vein of Labbé ( Figure 35.4 ).

    Figure 35.4, U-shaped dural incision, with the base at the skull base. The vein of Labbé is shown after dural flap elevation.

  • The temporobasal veins and the transverse sinus are typically encountered. These venous structures often have a reciprocal flow with the vein of Labbé. The infratemporal veins may be sacrificed with adequate control.

  • With this approach the middle fossa structures can be reached, including foramen ovale, arcuate eminence, the greater superficial petrosal nerve and the temporal lobe.

  • For an extradural approach, the middle fossa dura can be elevated, detaching it from the bone at the temporal fossa, with careful dissection of the greater superficial petrosal nerve ( Figure 35.5 ).

    Figure 35.5, The petrous bone can be drilled along the line that bisects the angle formed by the long axis of the arcuate eminence and the greater superficial petrosal nerve, exposing the internal acoustic canal.

  • For an extradural approach, at this stage the middle fossa dura can be elevated, detaching it from the bone at the temporal fossa. Ligation of the middle meningeal artery at the foramen spinosum may be necessary, to improve dural elevation.

  • At this point the microscope can be brought to the field. Considering the tumor characteristics, the resection can start in the usual fashion.

Pearls

  • The main risk of this approach is injury to venous structures (e.g. vein of Labbé, temporobasal veins and the superior petrosal vein and sinus), which could have consequences such as brain and brainstem edema and temporal lobe infarcts. Magnetic resonance venography is recommended in order to identify the drainage of the vein of Labbé, for surgical planning.

  • Brain relaxation is important to improve temporal lobe retraction and facilitate the tumor dissection. If adequate relaxation is not accomplished, lesions that are located in the nondominant medial temporal lobe or in the middle incisural space can be accessed via a transcortical approach, resecting a portion of the inferior temporal gyrus. This maneuver also avoids injury to the vein of Labbé.

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