Anterior and Subtemporal Approaches to the Infratemporal Fossa

Diagnostic and Staging Work-Up

Owing to the inaccessibility of the ITF to physical examination, radiographic imaging is a crucial component of the evaluation. Computed tomography (CT) and magnetic resonance imaging (MRI) are fundamental to the decision-making; therefore, they should be obtained using standard skull base protocols. CT is superior to MRI for the evaluation of the bony structures, showing remodeling or erosion of the neurovascular foramina or other bones of the skull base. MRI better delineates the soft tissue planes, the interface between the tumor and other soft tissues, and the presence of the tumor along neural and vascular structures ( Fig. 49.1 ). In most instances CT and MRI are complementary.

Another paramount question is the relationship of the tumor with the ICA. Magnetic resonance angiography (MRA) and computerized tomography angiography (CTA) provide noninvasive assessment of the vasculature of the ITF and brain. If preoperative embolization of the tumor is indicated (e.g., juvenile nasopharyngeal angiofibromas, paragangliomas), digital subtraction angiography is preferred over MRA. Angiography provides important information regarding the vascularity of the tumor, its relationship to the ICA, and the cerebral circulation and its collateral blood supply. Neither angiography nor MRA is adequate, however, to predict the adequacy of the collateral intracranial circulation reliably if the sacrifice of the ICA is necessary.

If the risk for injury or sacrifice of the ICA is high, the collateral cerebral blood flow may be evaluated using angiography-balloon occlusion with xenon CT (ABOX-CT). A nondetachable balloon is inserted in the ICA via the femoral artery. The balloon is inflated for 15 minutes while the patient is monitored for any clinical neurological deficit. If the patient does not develop any deficit, the balloon is deflated and the patient transferred to a CT suite. A mixture of 32% xenon and 68% oxygen is administered via a face mask for 4 minutes. CT shows the distribution of xenon, which reflects the blood flow within the cerebral tissue, providing a quantitative assessment of milliliters of blood flow per minute per 100 g of brain tissue. The process is repeated after reinflation of the arterial balloon. A computer calculates the differential of the xenon diffusion in the brain before and after the balloon inflation, thereby identifying patients at risk for ischemic stroke secondary to reduced blood flow after occlusion of the ipsilateral ICA ( Table 49.1 ).

Despite a negative ABOX-CT testing, patients can sustain ischemic brain injury because of the loss of collateral vessels that are not assessed by balloon occlusion testing (“watershed area”), or because of embolic phenomena. In addition, this test is performed under ideal and controlled circumstances; thus, it does not account for the possibility of episodes of hypoxia, hypotension, or electrolyte and acid-base disturbances that may alter the brain’s hemodynamics. Every effort should be made to preserve or reconstruct the ICA and to diminish the possibility of embolus formation during the surgery. The other techniques that provide information regarding the collateral cerebral blood flow include single photon emission CT (SPECT) with balloon occlusion and transcranial Doppler.

The histological diagnosis should be obtained before the extirpative surgery whenever possible. Tumors amenable to a punch or open biopsy are approached in this manner. Tumors that are in deeper planes may be sampled by fine-needle aspiration or core-needle biopsy. Rarely, a histological diagnosis cannot be obtained before the approach because of the intrinsic limitations of a needle biopsy. Under these circumstances, a frozen section analysis, obtained via a skull base approach, may be sufficient to justify the resection of the tumor. The vital neurovascular structures, such as the ICA, the eye, and cranial nerves, should not be sacrificed, however, based on a frozen section analysis.

The extent of the evaluation to exclude regional or distant metastasis or to determine that an ITF tumor represents a metastasis is dictated by the histological type and stage of the tumor. A CT scan of the neck is more sensitive than is a physical examination for the detection of regional lymphadenopathy. Patients presenting with tumors that metastasize hematogenously (sarcoma, melanoma) should undergo a CT scan of the chest and abdomen and a bone scan. Alternatively, a PET/CT may be used to rule out metastatic disease. Cytology of the cerebrospinal fluid (CSF) is advised for patients with tumors that have invaded the dura. These patients are also at risk for “drop metastasis,” which should be excluded by spinal MRI.

Rehabilitation Considerations

Functional or neurological deficits that are identified preoperatively should be considered during the surgical planning and postoperative care. These deficits often have a significant impact on the recovery and functional rehabilitation of the patient.

Dysfunction of the trigeminal nerve, masticator muscles, or both is commonly underdiagnosed. The cutaneous and corneal sensation should be assessed preoperatively. Corneal anesthesia associated with concomitant facial nerve palsy requires aggressive measures to prevent corneal injury.

The lateral deviation of the jaw during opening may reflect weakness, paralysis, or invasion of the ipsilateral pterygoid muscles, or dysfunction of the temporomandibular joint (TMJ). Likewise, trismus may be due to a mechanical restriction caused by the bulk of the tumor, ankylosis of the TMJ, scarring, tumor tethering, or pain. The nature of the trismus is an important consideration in the perioperative management of the patient’s airway. Trismus secondary to pain resolves with the induction of general anesthesia, thus allowing a safe oral endotracheal intubation. In patients with mechanical trismus, an awake nasotracheal intubation with fiberoptic endoscope guidance may be performed if it is anticipated that surgery would correct the trismus. Otherwise, a tracheotomy, performed under local anesthesia, is the safest perioperative airway.

Neoplastic invasion of the facial nerve may manifest with facial weakness or paralysis, facial spasms, epiphora, facial spasms, and dysgeusia. Significant destruction of the facial nerve fibers by the tumor may occur before the patient develops clinical signs. A gold or platinum weight implanted in the upper eyelid or a surgical tightening of the lower lid may be necessary to protect the cornea.

Hearing loss caused by a tumor of the ITF may be conductive, resulting from eustachian tube dysfunction, or sensorineural, resulting from tumor involvement of the temporal bone or posterior cranial fossa. A myringotomy, amplification, or both facilitate communication with the patient.

Deficits of the lower cranial nerves (CN IX, X, XI, and XII) are often associated with tumors that originate in the parapharyngeal space, tumors that extend to the jugular foramen, or both. Patients with deficits of CN IX, X, and XII present with varying degrees of swallowing or speech problems, such as hypernasal or slurred speech, nasal regurgitation, dysphagia, aspiration, and dysphonia. The findings on physical examination reflect the involvement of specific cranial nerves, and include decreased elevation of the palate, decreased mobility and strength of the tongue with deviation to the involved side on protrusion, decreased supraglottic sensation, pooling of secretions in the hypopharynx, ipsilateral vocal cord paralysis, and decreased bulk and strength of the sternocleidomastoid and trapezius muscles. Patients with partial deficits of the lower cranial nerves (paresis) often experience a complete deficit (paralysis) after surgery, resulting in increased dysphagia and aspiration. Consequently, a tracheostomy for tracheal toilet and a gastrostomy tube for nutrition and hydration are often necessary during the perioperative period.

Laryngeal framework surgery (i.e., medialization laryngoplasty or thyroplasty I) performed during the extirpative surgery or during the early postoperative period improves the glottic closure and decreases the risk for aspiration, often obviating the need for a tracheotomy for the sole purpose of a tracheopulmonary toilet. Laryngeal framework surgery allows the patient to compensate for swallowing deficits associated with an ipsilateral laryngopharyngeal paralysis by optimizing the remaining function of the contralateral side. Laryngeal framework surgery, however, does not restore the motor or sensory function. Therefore, these patients remain at a higher risk for aspiration and nutritional deficiencies. Collaboration with an experienced speech-language pathologist and nutritionist (i.e., dietician), who can assist with the monitoring of the patient and the diet modifications and provide intensive swallowing therapy, is crucial to prevent the pulmonary and nutritional complications of dysphagia and aspiration. In patients with severe deficits or in patients with cognitive problems, strong consideration should also be given to the placement of a gastrostomy tube to facilitate postoperative feeding and decrease the risk of prandial aspiration.

Velopharyngeal insufficiency may be ameliorated by a palatal lift prosthesis that thrusts the soft palate against the posterior pharyngeal wall, thereby closing the gap. Alternatively, a pharyngeal flap or a palatopexy may be performed. These are also indicated in patients who do not tolerate the prosthesis.

Reconstructive Considerations

Most commonly, a temporalis muscle transposition flap is adequate to separate the cranial cavity from the upper aerodigestive tract and obliterate the dead space. A microvascular free flap is indicated when the temporalis muscle or its blood supply is sacrificed as part of the oncological resection; when the patient requires a complex resection involving composite tissue flaps with skin, bone, or both; or when the extirpative surgery leads to a massive soft tissue defect and dead space. Ideally, every reconstruction should strive to “replace like with like”; thus, soft tissue defects are reconstructed with myocutaneous or fasciocutaneous free flaps such as from the anterolateral thigh, latissimus dorsi, or rectus abdominis. In order to choose the best flap, one should also consider the amount of soft tissue removed, the volume of dead space to be obliterated, and the patient’s body habitus. Flaps with vascularized bone are ideally used when the zygoma or orbital rim are removed (free bone grafts or prosthetic implants should be used with caution if the patient has received preoperative radiotherapy or if adjuvant radiation therapy is anticipated). Chimeric flaps, such as the scapular tip–thoracodorsal arterial perforator flap, should be considered for more complex defects ( Fig. 49.2 ). These needs can be anticipated during the surgical planning so that the microvascular surgeon and the patient are informed accordingly.

Ideally, functional and cosmetic deficits created by the tumor or the surgery should be addressed concomitant with the oncological resection. When a temporary facial palsy is anticipated, corneal protection using lubricants, a temporary lateral tarsorrhaphy, or both is usually adequate. Grafting of the facial nerve involves a longer recovery period, however. The insertion of a gold or platinum weight implant into the upper eyelid is advisable. When an immediate reconstruction of the facial nerve is impossible, static fascial slings or muscle transpositions are indicated. Lower cranial nerve deficits may be ameliorated by laryngeal framework surgery, tracheotomy, or laryngotracheal separation, as previously discussed.