Introduction

The “infratemporal approach” explores the anatomic steps in performing endoscopic skull base surgery of the infratemporal fossa (ITF). A detailed anatomic description of the steps is provided. Critical landmarks for safe dissection are described and common instrumentation to access this region is provided. From this knowledge, we are able to predict functional outcomes for the patient and prepare for management of postoperative deficits. Common tips learned from the author′s experience are provided to perform safe and minimally disabling surgery for the patient while obtaining the oncologic goals of surgery.

25.1 Indications

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  Juvenile nasopharyngeal angiofibroma.

  
  
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  Trigeminal neurilemmoma.

  
  
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  Meningioma.

  
  
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  Lymphoproliferative disorders (biopsy only).

  
  
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  Sinonasal malignancy.

  
  
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  Nasopharyngeal carcinoma.

  
  
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  Palliative debulking of malignancies.

  
  
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  Diagnostic biopsy.

25.2 Infratemporal Fossa Limits

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  Medial: The lateral pterygoid plate.

  
  
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  Lateral: The ramus of the mandible.

  
  
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  Posterior: The articular tubercle of the temporal bone, spina angularis of the sphenoid bone, and carotid sheath.

  
  
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  Anterior: The infratemporal surface of the maxilla.

  
  
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  Superior: The greater wing of the sphenoid bone and under surface of the temporal squama containing the foramen ovale.

  
  
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  Inferior: The medial pterygoid muscle attaching to the mandible.

25.3 Surgical Steps

The patient is placed in a supine position on the operating table. After the application of general anesthesia and secured intubation, pledgets soaked in oxymetazoline, a selective α-1 agonist and partial α-2 agonist, are guided into the nasal cavity for topical decongestion. Following decongestion, 1% lidocaine with 1:100,000 epinephrine is injected into the septum, middle turbinate, uncinate, inferior turbinate, the inferior border of the third basal lamella, and the mucosa overlying the canine fossa (if Caldwell-Luc is utilized) ipsilateral to the lesion to decrease mucosal bleeding. It is recommended to allow several minutes for decongestion prior to surgery; during this time, images for surgical guidance are loaded onto the preferred hospital system and the patient is registered for neuronavigation.

The standard endoscopic infratemporal approach at the author′s institution is through a uninostril endoscopic approach with the possible assistance of a Caldwell-Luc approach (described later). Some institutions also perform a Denker′s approach to improve ease of instrumentation and surgical access.1 Using a 0-degree rigid nasal endoscope (e.g., Karl Storz or Medtronic), the middle turbinate is medialized and then subtotally removed with nasal sinus scissors (Medtronic) with special attention not to injure the lateral lamella at the cribriform plate ( Fig. 25.1a–c ). The uncinate is removed in its entirety with a back-biting forceps, allowing access to the natural ostium of the maxillary sinus ( Fig. 25.2a–c ). A large maxillary antrostomy is performed with rongeurs and 4.0-mm microdebrider; the inferior turbinate is removed with nasal sinus scissors for access to the inferior extent of the approach ( Fig. 25.3 ). This step allows visual access of the posterior wall of the maxillary sinus corresponding to the anterior wall of the pterygopalatine fossa (PtPF).

If a second port of access is needed for instrumentation or increased lateral access, a Caldwell-Luc incision is placed under the ipsilateral lip over the canine fossa. This incision, approximately 4 cm in length, is made preserving at least a 5-mm cuff of inferior gingivobuccal tissue for closure at the end of the surgery. The incision is carried down through the periosteum. The periosteum is then elevated over the anterior surface of the maxillary bone. The superior limit is the inferior alveolar nerve and canal. The medial limit is the piriform aperture. The lip is retracted with self-retaining instruments with wet gauze padding protecting the lip from injury ( Fig. 25.4 ). The anterior wall of the maxillary sinus is then removed, allowing full sinus access. In case an endoscopic Denker or Sturmann-Canfield approach is chosen, the piriform aperture is removed laterally with rongeurs.

With a 0-degree endoscope through the ipsilateral nostril, the mucosa lying on the medial surface of the crista ethmoidalis is elevated, allowing visualization of sphenopalatine artery (SPA) exiting its canal. This is usually centrally located at the lateral attachment of the basal lamella (for more details, please check Chapter 8). A 2-mm Kerrison rongeur is used to remove the bone from the posterior bone wall of the maxillary sinus exposing the PtPF. A 3-mm high-speed diamond drill with continuous saline irrigation can be used to remove thick bone particularly in the inferior posterior quarter and lateral bone of the maxillary sinus.

The periosteum overlying the soft-tissue contents of the PtPF is removed with Kerrison rongeurs or sharp microscissors exposing the course of the SPA ( Fig. 25.5a, b ). Often the SPA has a random course through the PtPF. To prevent inadvertent vascular injury and to increase exposure, care is taken to place titanium vascular clips on the most proximal segment of the artery accessible with an endoscopic clip applier ( Fig. 25.5c ).

Fat within the PtPF may be removed with a rongeurs, Frazier suction, or soft-tissue ultrasonicator to allow visualization of the inferior orbital nerve, pterygopalatine ganglion, vidian nerve, and descending palatine nerve. It is important to preserve these structures when possible to avoid postoperative paresthesias of the ipsilateral midface and palate.

The anterolateral surface of the lateral pterygoid plate is then identified with palpation and image guidance. The attachments of the lateral pterygoid muscle are then elevated from the plate with a caudal elevator ( Fig. 25.6a ). Sometimes, use of a 3-mm high-speed diamond drill with irrigation helps to obtain this plane. Depending on the tumor type, the lateral pterygoid muscle may be resected to gain further exposure. In these cases, patients often suffer from trismus and an asymmetric bite requiring postoperative physical therapy. Following the lateral edge of the pterygoid plate and greater wing of the sphenoid leads to foramen ovale and the mandibular nerve ( Fig. 25.6b, c ). Nerve injury or sacrifice will cause paresis and/or paralysis of the muscle of mastication and paresthesias, numbness, and/or pain of the lower third of the face and ipsilateral tongue.2

Posterior and lateral to foramen ovale is the foramen spinosum with the middle meningeal artery. Careful placement of a titanium clip or pistol-grip, bipolar cautery can control this vessel. Avoid cauterizing too close to the foramen to avoid intracranial retraction and subsequent epidural hematoma. The cervical segment of the carotid artery (C1) is posterior and lateral to foramen spinosum ( Fig. 25.7a, b ). Although not in the ITF, care must be taken to inspect the course of the C1 segment due to the random course this artery may take in the neck prior to entering the skull base.3 The greater wing of the sphenoid bone limits superior exposure of the ITF. The floor of the maxilla containing the dental roots of the molars limits inferior access. The medial and lateral borders of the ITF should be easily accessible.