Summary
This chapter reviews the anatomy, pathology, and clinical evaluation of the infratemporal fossa and describes the surgical management of this complex structural space. Because of its proximity to critical neurovascular structures, resection of tumors in this space requires precise surgical planning. Historically, many open approaches have been available to the surgeon, which can be tailored to the extent and behavior of the tumor. Beginning in the 1980s, advances in endoscopic endonasal techniques have catalyzed efforts to minimize surgical morbidity. A multidisciplinary team should be assembled to perform a comprehensive evaluation of the patient and establish a coordinated treatment plan.
19 Tumors of the Infratemporal Fossa
19.1 Introduction
Tumors of the infratemporal fossa (ITF) can arise primarily or can invade by direct extension from surrounding structures, such as the parotid gland, upper aerodigestive tract, nasopharynx, paranasal sinuses, temporal bone, pterygopalatine fossa (PPF), and parapharyngeal space (PPS). Many of these tumors require surgery, which can carry significant risk to the critical neurovascular structures contained within this space. Proper evaluation requires intimate knowledge of the anatomy and a multidisciplinary approach to treatment planning. Management decisions should ensure both effective eradication of disease and acceptable function and cosmesis.
19.2 Surgical Anatomy
The ITF, located medial to the vertical ramus of the mandible and zygomatic arch and lateral to pharynx, is not lined by a single consistent fascia and lacks rigid borders. Anteriorly, it is limited by the posterior surface of the maxilla, and its posterior border is the mastoid and tympanic temporal bone. Its superior border is the inferior surface of the greater wing of the sphenoid, through which communication with the middle cranial fossa occurs through the foramina ovale and spinosum.
Its medial and inferior borders have varying definitions. Medial limits may be defined by the bony landmarks of the lateral pterygoid plate, the lateral portion of the clivus, the first cervical vertebra, and the inferior surface of the petrous temporal bone. Soft tissues can also delineate the medial border: the superior pharyngeal constrictor and tensor and levator veli palatini. Inferior limits are variably defined in some descriptions; some sources consider the lateral inferior insertion of the medial pterygoid muscle or the posterior belly of the digastric muscle as the inferior boundary of the ITF.1
The ITF communicates with the orbit through the inferior orbital fissure and with the PPF through the pterygomaxillary fissure. Tumors can spread to and from surrounding spaces through these openings or along venous connections. Careful attention must be paid to these potential corridors of spread, which are often best evaluated using MRI.
The contents of the ITF include the medial and lateral pterygoid, masseter, and temporalis muscles, the deep lobe of the parotid gland, and neurovascular elements: the mandibular division of the trigeminal nerve (V3), chorda tympani branch of the facial nerve, otic ganglion, jugular vein, internal carotid artery (ICA), internal maxillary artery, and pterygoid venous plexus.
19.3 Regional Pathology and Differential Diagnosis
Because the contents of the ITF include multiple tissue types, a variety of tumors can occur there. Common benign neoplasms of the ITF include schwannomas, pleomorphic adenomas, vascular lesions (arteriovenous malformations, paragangliomas), and meningiomas. Less commonly, deep lipomas and inflammatory pseudotumor may also arise in the ITF.
Malignant primary tumors of the ITF include rhabdomyosarcoma, osteosarcoma, fibrosarcoma, and malignant hemangiopericytoma. The ITF can also be involved by spread of tumors from adjacent spaces. Malignant salivary tumors can originate from the aerodigestive tract, parotid gland, or microscopic minor salivary rests. Locally aggressive mucosal cancers can extend from the oral cavity, sinuses, and nasopharynx. Hematologic proliferative disorders, such as lymphoma, plasmacytoma, or histiocytosis X, may also present in the ITF.2 Occasionally, distant metastases may appear in the ITF, such as from the kidney, thyroid, and adrenal glands.3
19.4 Clinical Assessment
The interview with the patient should address any history of previous cancers or tumors in the head and neck or other locations, particularly details of management, including prior head and neck surgery or radiation. The patient’s medical health, functional status, alcohol and tobacco use are also important. The history of present illness should include a thorough investigation of any neurologic complaints, with an emphasis on any cranial nerve (CN) dysfunction, which can sometimes be quite subtle and easily missed unless careful examination is performed.
Dysfunction of the trigeminal nerve is common with tumors of the ITF. This may present as localized numbness or dysesthesia in the distribution of the trigeminal nerve, especially V2 and V3. Malocclusion, deviation of the jaw, or other dysfunction of mastication may be present due to mass effect or denervation atrophy of the masticator muscles. Trismus suggests possible spread of tumor into the pterygoid musculature or the temporomandibular joint (TMJ).4
Facial weakness suggests tumor involvement either by nerve compression or direct invasion. A detailed assessment of the function of all facial nerve (VII) branches should be carefully documented in the medical record, both to assess initial status and to serve as a baseline for comparison in the case of postoperative dysfunction. Tumors approaching the jugular foramen may cause deficits of CNs IX through XII.5 Any complaints of dysphagia, cough, choking episodes, or aspiration should be thoroughly investigated. Any of these deficits warrant further evaluation by a speech-language pathologist, often in conjunction with a videoradiographic examination of swallowing. Again, surgery or radiation may worsen these problems, highlighting the importance of precise documentation of pretreatment status. The presence of dysarthria or tongue atrophy, indicating CN XII dysfunction, is significant for both treatment planning and postoperative rehabilitation.
A detailed otologic history and exam should be conducted, including audiogram and vestibular testing as indicated. Eustachian tube (ET) compression by tumor can lead to middle ear effusion and conductive hearing loss. Invasion of the temporal bone and middle or posterior cranial fossa can lead to conductive or sensorineural hearing loss and vestibular dysfunction.
The ITF is relatively inaccessible to direct inspection and palpation, but indirect or secondary signs can be appreciated on careful physical exam. Subtle swelling of the temporal area above the zygomatic arch may be noted. Visual changes such as proptosis, diplopia, and blurring may indicate orbital or cavernous sinus involvement by tumor. Ophthalmologic history should be taken, and visual acuity and visual fields should be assessed. Any deficits should trigger a referral to an ophthalmologist.
Finally, the patient’s airway must be thoughtfully assessed. Flexible fiberoptic rhinoscopy and laryngoscopy will offer the most thorough visual examination of the upper airway. Patients who have significant trismus may require fiberoptic intubation or even a tracheostomy if a major resection and reconstruction are planned. If the management plan includes endoscopic surgery, nasal endoscopy is helpful to assess the adequacy of the intended surgical corridor.
19.5 Diagnostic Imaging
Because accessibility for direct physical examination of the ITF is limited, radiographic imaging is essential in determining precise tumor location and extent. Bony changes are best seen on CT. Frank bone erosion, especially if mottled or irregular, indicates aggressive behavior and suggests malignancy, whereas remodeled bone with smooth or tapered borders may be a sign of slow compression from benign tumor growth. Widening of cranial foramina is best seen on CT. MRI is best for evaluation of soft tissue planes and identifying neural invasion, tumor extension into the orbit, and involvement of adjacent dura. It is important to obtain fat-suppressed T1-weighted contrast-enhanced MRI. These images will more accurately display tumor-related contrast enhancement and reduce potential confusion due to high signal from surrounding adipose tissue and fat-containing bone marrow of the skull base.
Evaluation of the ICA is always important; ITF tumors located lateral to the ICA at the carotid foramen will require an external or combined approach. If there is any concern for ICA involvement following initial imaging, a CT angiogram (CTA), MR angiogram (MRA), or formal angiogram is indicated. Preoperative evaluation of collateral cerebral blood flow with a balloon occlusion test should be considered if intraoperative manipulation of the ICA is likely. Consultation with a neurovascular surgeon is warranted if intraoperative vascular bypass is a possibility.
19.6 Preoperative Preparation
Tissue biopsy to determine the precise pathologic diagnosis and help predict likely biologic behavior is necessary before considering a treatment plan for ITF tumors, with very few exceptions. This information is critical. Although management of many tumors will require surgical resection, others (e.g., lymphoma, plasmacytoma) will best be treated with other modalities.
An image-guided fine-needle aspiration biopsy is preferable for the majority of tumors of the ITF, having lower risk and morbidity than an open biopsy. Transnasal endoscopic biopsy is possible for tumors of the medial ITF, which can usually be accessed well through either the maxillary sinus or the nasopharynx. Highly vascular lesions such as glomus tumors, when suspected on imaging, should usually not be biopsied if they fit classic radiographic criteria for diagnosis. When necessary, such as when a fine needle aspiration (FNA) has been inconclusive, open biopsies (through the upper neck or temporal region) are sometimes justified. Open biopsies of the ITF through the mouth are generally discouraged due to their potential for hemorrhage and contamination.
A multidisciplinary tumor board should evaluate each case and assist in deciding optimal treatment plans, taking into consideration the patient’s overall health and fitness for surgery. When applicable, alternate treatment plans can be considered, such as when patients have unacceptably high risk for surgery or when a patient will not accept the risk of certain treatments (e.g., sacrifice of facial nerve or carotid artery). Reconstructive needs and options are assessed preoperatively, and reconstructive surgeons are engaged as needed. In most cases, reconstruction is performed immediately after the surgical resection, although occasionally it may be electively delayed for a second-stage surgery if there is uncertainty about tumor margins.
Preoperative counseling should inform the patient that intact preoperative CN function is no assurance of functional preservation. In addition to injury to CNs, other operative risks include cerebrospinal fluid (CSF) leak, injury to the orbit, injury to adjacent brain, and vascular injury, including ICA injury, with risks of resultant cerebrovascular accident or death.
Facial nerve monitoring is helpful in cases in which the facial nerve may be at risk. Select CN monitoring, such as of the vagus nerve via electromyographic endotracheal tube or of the spinal accessory nerve via the trapezius, is indicated in some cases.6 If neurophysiologic monitoring is performed, paralytic agents should be avoided by the anesthesia team.
Antibiotic prophylaxis should provide coverage against flora of the skin and upper aerodigestive tract. If imaging reveals skull base or intracranial invasion, neurosurgical consultation is essential. If intracranial surgery is anticipated, the use of an antibiotic that exhibits good penetration of the blood–brain barrier should be considered. A lumbar drain should be considered if significant intradural dissection with risk of postoperative CSF leak is anticipated. Tumor involvement of the ICA with failed balloon occlusion test is generally a contraindication for surgery, as is extensive invasion of brain parenchyma by a malignancy.
19.7 Surgical Technique
The precise location and extent of the tumor, along with its histology and vascularity, will dictate the optimal surgical approach. The most commonly used approaches to the ITF include the preauricular, postauricular, transtemporal, facial translocation, and endoscopic endonasal approaches. Each has its own advantages and limitations, discussed hereafter.
Many tumors of the ITF can be accessed through a preauricular approach 7 (Fig. 19.1), including tumors that arise in the deep lobe of the parotid gland, the mandible, the TMJ, the greater wing of the sphenoid, or the anterior temporal bone. (Note: This approach does not allow safe resection of the entire temporal bone or control of the infratemporal facial nerve or jugular bulb.) A postauricular approach 7 (Fig. 19.2) is well suited for tumors originating within, or substantially involving, the temporal bone. Common indications include meningiomas, facial schwannomas, arteriovenous malformations (AVMs), smaller glomus tumors, and certain malignancies of the temporal bone that extend downward into the ITF.
The lateral infratemporal approaches (Fig. 19.3) described and popularized by Ugo Fisch8 are appropriate for a wide variety of ITF tumors, including large glomus tumors and other tumors that extend from the mastoid and middle ear to the infratemporal skull base, and those that involve the carotid artery or carotid canal. Surgery for such tumors may require rerouting of the facial nerve, which can be readily achieved with these approaches. Prof. Fisch described a system of transtemporal (otologic) approaches, called types A, B, and C, with progressively more exposure for each type (later a more limited type D was also described). These approaches are thus quite adaptable for many different lesions that extend into the ITF, ranging from tumors of the ear canal to those of the nasopharynx and clivus.
The facial translocation approach (Fig. 19.4) described by Ivo Janecka9 was developed as an alternative to address very extensive lesions of the ITF, central skull base, masticator space, pterygomaxillary fossa, and paraclival region as well as certain tumors of the nasopharynx extending into the ITF. The chief advantage of this approach is that it allows direct, open-field access in three dimensions for maximal external access to tumor and critical structures.
The introduction of endoscopic endonasal approaches (Fig. 19.5) has offered a “minimally invasive” alternative to open surgery for ITF tumors. Not long after endoscopic sinus surgery was introduced, it became clear that the endoscope could often be helpful for diagnostic biopsy of tumors in the medial ITF. With introduction of more sophisticated tools (e.g., high-definition video images, image-guided intraoperative CT- and MRI-navigation, and improved methods of endohemostasis), the use of the endoscopic technique has expanded to include totally endoscopic tumor resections. At first this was applied to tumors within just the medial ITF, but endoscopic techniques are now used to resect many tumors deep in the ITF, including jugular foramen and even extension into the PPS.10 With endoscopic resections, as opposed to open craniofacial resections, significant decreases in operative time, hospital stay, and blood loss have been reported.11 , 12 It has also been argued, based on studies of CT images, that open approaches do not afford a substantially larger working space or visual field.13 In properly selected patients, endoscopic approaches can be quite effective.
19.7.1 Positioning
For open procedures, the patient is placed supine on the operating table and the head is turned to the side contralateral to the lesion. When intracranial neurovascular work is anticipated, the head may be fixed in a Mayfield headrest or in fixation pins. The patient’s body is secured with straps and carefully cushioned to avoid pressure points; this facilitates rotation of the entire table to enhance visualization. Hair is parted, clipped or shaved along the path of the planned incision, and the face, scalp and neck are prepped in sterile fashion.
For endoscopic approaches, the patient is positioned supine in the operating table with the head in neutral position. The head of the table is raised, in a reverse Trendelenburg position, to decrease central venous pressure. The nasal cavity is prepared with pledgets bearing topical decongestant. The eyes are lubricated but kept accessible for intraoperative monitoring of the pupils and globes. A 3D stereotactic navigation system, though not absolutely necessary, can aid in confirmation of landmarks and locations of structures at the skull base and can be helpful in defining trajectory and assessing completeness of resection. Navigation should be based on thin-cut CT images obtained immediately prior to surgery. The system is set up prior to the start of the case and calibrated using reliable external surface anatomy.
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