17.1 Introduction

Incidence of nasopharyngeal carcinoma (NPC) has distinct racial and geographic variations. The tumor is rare in most parts of the world, with incidence for either sex of less than 1 per 100,000 persons per year. However, it is endemic in the southern part of China, including Guangdong Province, where the incidence of NPC is among the highest in the world.1

NPC often demonstrates highly aggressive behavior, with extensive local tumor infiltration, early and multiple/bilateral lymph node metastasis, and a high chance of hematogenous metastasis to the bone, lungs, liver, and distant nodes. Local skull base erosion and intracranial extension are not uncommon. The tumor is sensitive to radiotherapy and has an overall survival of up to 90%, especially for patients who have early-stage disease2; treatment outcomes for late-stage tumors have also dramatically improved with use of concurrent chemoradiation.3 ^,​ 4 ^,​ 5

The overall rate of local tumor recurrence in the nasopharynx after primary treatment is approximately 10%.6 Surgical salvage of recurrent tumors offers better overall survival and quality of life than re-irradiation does.7 ^,​ 8 ^,​ 9 Conversely, surgical access to the nasopharynx is difficult because of its location10 and its proximity to vital structures. Furthermore, complications of surgery, such as meningitis, extensive osteoradionecrosis of the skull base, and torrential bleeding from carotid artery blowout, are potentially life-threatening. Adequate preoperative assessment and meticulous intraoperative technique are essential to the success of surgery.

17.2 Surgical Anatomy

The nasopharynx is located at the posterior end of the nasal cavity. It is bounded superiorly by the floor of the sphenoid sinuses and by the clivus as the roof that slopes posteriorly and inferiorly (Fig. 17.1). Inferiorly the nasopharynx is continuous with the oropharynx at the level of the soft palate. Anteriorly it is bounded in the midline by the posterior edge of the nasal septum and the vomer of the sphenoid bone. On each side, the nasopharynx is continuous with the nasal cavity via the choanae. Posteriorly the nasopharynx is bounded by the prevertebral muscles, the clivus, and the vertebral body of the first cervical vertebra. The lateral walls of the nasopharynx are formed by the Eustachian tube cushions on each side. The opening of the auditory tube leads to the middle ear. The auditory tube is cartilaginous in its distal third and passes into a bony canal as it traverses superiorly and laterally toward the middle ear, where it communicates on its anteroinferior wall. The levator veli palatini and the tensor veli palatini muscles are attached to the auditory tube.

The nasopharynx consists of an epithelium, deep to which is the lamina propria, followed by the superior constrictor and prevertebral muscles. The epithelium is mainly pseudostratified ciliated columnar cells, with transition to squamous cells inferiorly as it merges with the oropharynx. The lamina propria is richly filled with lymphocytes. Enveloping the nasopharynx laterally is the superior constrictor muscles. A thick fascia, the pharyngobasilar fascia, is located superior to this. This fascia lies anterior to the prevertebral muscles and its covering fascia. Laterally the pharyngobasilar fascia is continuous with the prevertebral fascia, medial to the carotid sheath, which forms the boundary of the parapharyngeal space.

Understanding of the course of the internal carotid artery is crucial to avoid inadvertent injury during nasopharyngectomy. After originating from the common carotid artery, the cervical portion of the internal carotid artery ascends about 2.5 cm posterior to the coronal plane of the pterygoid plates, lateral to the lateral pterygoid plate. It then enters the bony carotid canal of the petrous bone, where it passes medially and superiorly, making its first turn. Within this bony carotid canal, it is located posterior and medial to the auditory tube. As the internal carotid leaves the carotid canal medially, it reaches close to the lateral edge of the sphenoid sinus, where it now ascends in a medial and superior direction. Here the internal carotid artery passes posterior and above the foramen lacerum. The internal carotid artery finally enters the cranial cavity via the foramen lacerum, posterior to the anterior clinoid process. It traverses the cavernous sinus and divides into the anterior and middle cerebral arteries.

In nasopharyngectomy, depending on the extent of the tumor, the lateral resection margin often requires that the pterygoid plates be completely or partially transected. After the pterygoid plates are transected, the internal carotid artery will be in proximity. It may be identified by gently dissecting through the fibrofatty tissue in the pterygopalatine fossa and palpating for pulsation or by using intraoperative Doppler ultrasonography or MRI stereotaxy. A sheet of connective tissue, the pharyngobasilar fascia, is superficial to the internal carotid artery and must be breached before reaching the wall of the artery.

17.3 Regional Pathology and Differential Diagnosis

In endemic regions, such as South China (particularly Guangdong Province), Southeast Asia, northern circumpolar region, and the Mediterranean basin, NPC is the most common tumor arising from the nasopharynx. More than 95% of these tumors are of World Health Organization (WHO) type III (undifferentiated, nonkeratinizing), which is associated with Epstein-Barr virus (EBV) infection. Other differential diagnosis of tumors in the region includes squamous cell carcinoma, salivary gland tumors (mucoepidermoid carcinoma, adenoid cystic carcinoma), adenocarcinoma, and sarcoma. Head and neck lymphoma may also present with tumor involving the nasopharynx.

17.4 Clinical Assessment

In endemic areas, such as South China, NPC is the most common malignancy giving rise to nasal symptoms. Symptomatology of patients suffering from NPC can be divided into four categories: (1) nasal symptoms, (2) otological symptoms, (3) cranial nerve symptoms, and (4) neck symptoms.

A patient presenting with unprovoked epistaxis on just one side should raise concern about a malignant cause. In early tumors, bleeding is usually trivial and stops spontaneously after several minutes. New-onset persistent unilateral nasal obstruction is also more worrying, as nasal obstructions that have inflammatory causes are more likely to be bilateral and episodic. NPC patients frequently experience postnasal discharge that is bloodstained. The olfaction of NPC patients, however, is rarely affected, because the nasopharynx is quite far from the cribriform plate that houses the olfaction nerves.

NPC is frequently located near the fossa of Rosenmüller, so that disturbance of Eustachian tube function is seen on one side early in the disease’s progression. This disturbance causes unilateral otitis media with effusion, after which patients experience unilateral conductive hearing loss associated with low-pitch nonpulsatile tinnitus. Pasame ear. However, true otalgia and ear discharge are rare, because the tympanic membrane usually remains intact.

Neck swelling secondary to cervical lymphadenopathy is the most common presenting symptom of NPC. Up to 76% of NPC patients have enlarged cervical lymph nodes on presentation.11 Systemic symptoms, such as anorexia and weight loss, are uncommon in NPC, and distant metastasis should be suspected if such symptoms are present.

Physical examination of the nasal cavity begins with anterior rhinoscopy by a nasal speculum, but this is usually unrevealing in NPC patients. Postnasal space mirror examination provides a satisfactory view of the region in fewer than half of patients. Otoscopy should be carried out to look for the presence of otitis media with effusion, the presence of which should warrant endoscopic examination of the nasopharynx in all adult patients. The neck should be palpated carefully to look for the presence of cervical lymphadenopathy. The most common locations of metastatic lymph nodes from NPC are level II and the apex of level V, and it is not uncommon to have bilateral nodal involvement because of the decussation of the lymphatic supply of the nasopharynx. Finally, the cranial nerves, particularly the abducent nerve and the trigeminal nerves, should be examined, as up to 20% of patients have cranial nerve palsies on presentation.12

In patients who have suspicious symptoms or family history of NPC, blood should be tested for EBV serology, with positive EBV serology another indication for nasal endoscopy.13 The diagnosis of NPC is made on the basis of a positive biopsy result of the nasopharyngeal tumor visualized on nasal endoscopy. Early tumors tend to be near the fossa of Rosenmüller, which is just medial to the Eustachian tube. In patients who have a high clinical suspicion of suffering from NPC, cross-sectional imaging such as CT or MRI of the nasopharynx should be undertaken even if initial nasal endoscopy is unrevealing, with the aim of picking up the infrequent instances of submucosal tumors in which the nasopharyngeal mucosa can remain completely smooth. A targeted deep biopsy of the submucosal tumor identified on imaging can then be done to confirm the diagnosis.

17.5 Diagnostic Imaging

MRI has taken over CT as the primary imaging tool for the staging of NPC. Tumors are isointense or hypointense on T1-weighted images (relative to muscles) and intermediate hyperintense on T2-weighted images. Modest contrast enhancement is noted, but less than that seen in normal nasopharyngeal mucosa (Fig. 17.2).

Eighty-two percent of early tumors arise in the posterolateral recess of the nasopharynx, usually in the fossa of Rosenmüller.14 The fossa is located posterior to the torus tubarius on axial images and superior to it on the coronal images. The torus tuberous contains the cartilaginous portion of the Eustachian tube and the levator veli palatine. Anterior to the torus tubarius is the opening of Eustachian tube. Fluid collection in the middle ear cavity secondary to tumor obstruction or Eustachian tube dysfunction is commonly seen. Although ventral tumor extension to the choanal orifice is not uncommon, extensive disease extension into the nasal cavity is encountered only occasionally. Careful imaging examination of the nasal septum is essential, for tumor involving the roof of the nasopharynx may extend anteriorly to invade the septum.15

The retropharyngeal lymph nodes are the first echelon of nodes of lymphatic drainage of the nasopharynx. Most of them are seen at the C1/C2 level. Tumors extending posterolaterally may involve the carotid artery and the jugular and hypoglossal canal and thus affect cranial nerves IX, X, XI, and XII. Assessment of tumor involvement of the carotid is essential when planning surgery.

Locally advanced tumors have a propensity to extend superiorly and involve the base of skull. Invasion of the sphenoid sinus is common, as it is separated from the roof of the nasopharynx by only a thin plate of bone. Replacement of the normal high T1-weighted fatty marrow signal should raise suspicions of skull base involvement. The clivus, pterygoid plates, and body of the sphenoid are commonly involved (Fig. 17.2). The pterygopalatine fossa can be involved with disease extension via the sphenopalatine foramen. Once the fossa is involved, disease can spread to the orbit via the inferior orbital fissure, to the infratemporal fossa via the pterygomaxillary fissure, to the middle cranial fossae via the foramen of rotundum, to the foramen of lacerum via the vidian canal, and to the oral cavity via the greater palatine foramen.

Direct invasion of the base of skull is the most common manner of intracranial tumor extension.16 Sphenoid and the foramen of lacerum can be involved by direct tumor spread (Fig. 17.3). After the foramen lacerum is involved, the tumor will be sitting next to the internal carotid artery, which runs over the superior portion of the foramen lacerum.

Cranial nerve involvement is seen in 15 to 20% of patients who have NPC.16 ^,​ 17 ^,​ 18 Perineural spread, particularly through the mandibular division of the trigeminal nerve via the foramen ovale, has been shown to be the most common route of intracranial disease extension with the advent of MRI,19 ^,​ 20 but perineural spread can also involve the maxillary division of the trigeminal nerve with tumor extending through the foramen rotundum. Perineural invasions are best seen in fat-saturated postcontrast T1-weighted MR images in the coronal plane. Cranial nerve enlargement, irregularity, excessive enhancement, and foraminal enlargement with destruction are MR features of perineural spread. Effacement of the normal intraforaminal fat signal on T1-weighted images is also suggestive of perineural tumor invasion.21 The foramen ovale can be seen on the coronal images at and slightly ventral to the condylar head of the mandible. Dural involvement in the middle cranial fossae and involvement of the cavernous sinus and Meckel’s caves should be checked as well. Tumors that invade the cavernous sinuses can lead to multiple cranial nerve palsies, including oculomotor, trochlear, and the ophthalmic and maxillary divisions of the trigeminal and the abducent nerves.

17.6 Preoperative Preparation

Before contemplating salvage nasopharyngectomy, a thorough endoscopic examination of the nasopharynx and oropharynx is important. Suspicious mucosal ulceration should be biopsied for histological confirmation of tumor recurrence. For submucosal tumors, deep biopsy is required; in some patients, biopsy under general anesthesia is indicated. Fine-needle aspiration of cervical lymph nodes is useful for nodal staging, although its efficacy is diminished in cases of prior radiotherapy.22 Patients are assessed for fitness of general anesthesia, with particular attention to the stability of the cervical spine in patients who have osteoradionecrosis and to the presence of hypopituitarism. The presence of trismus from previous radiotherapy, which may cause difficulty in intubation during anesthesia, should be noted. If necessary, surgeons should be available during the induction of anesthesia and should prepare for the creation of a surgical airway should intubation fail. Preoperative dental assessment is important, and an obturator should be fabricated for postoperative application.

17.7 Surgical Technique

Although early recurrent tumors in the nasopharynx can be resected using an endoscopic or transoral robotic-assisted approach, the traditional open approach offers a wide exposure that is particularly advantageous for locally advanced tumor. Among the various open approaches described, the maxillary swing approach, first described in 1991,23 offers wide access to the ipsilateral nasopharynx and parapharyngeal space up to the infratemporal fossa. It offers access to the middle cranial base superiorly, the contralateral nasopharynx, and the oropharynx inferiorly. Exposure of the contralateral parapharyngeal space, however, is limited, so the approach is contraindicated in tumors infiltrating the contralateral parapharyngeal space.

17.8 Positioning

Patient is positioned supine, with neck extended. In general, intubation via the transnasal route is avoided to prevent trauma and bleeding from the tumor. Transoral intubation is preferred, although tracheostomy under local anesthesia should be considered in patients who have severe trismus after radiotherapy. Induction of anesthesia can subsequently be performed via the tracheostomy.

The ipsilateral eyelids are then apposed with a temporary tarsorrhaphy, with the contralateral orbital contents protected using watertight adhesives. The mid- and lower face are prepared with antiseptic solution and draped accordingly. If vastus lateralis muscle flap is indicated for reconstruction, the thigh is prepared and draped as well. The oral cavity is then cleansed with antiseptic solution.

17.9 Incision

A Weber-Ferguson-Longmire incision is placed on the side of tumor (Fig. 17.4). The subcillary incision is placed 5 mm inferior to the lower lid margin. The angle between the skin incisions at the subcillary region and the nasal sidewall should not be acute, so as to avoid ischemic necrosis of the tip of the angle, which is not uncommon after previous radical radiotherapy.

A palatal incision is placed along the gingiva in a curvilinear fashion on the ipsilateral side of the hard palate. It is then gently curved behind the last molar tooth.

17.10 Soft Tissue Dissection

Soft tissue dissection after the skin incision exposes the underlying osteotomy sites. However, it is crucial not to detach soft tissues from the underlying bone/periosteum to an excessive degree, so as to maximally preserve the blood supply to the maxillary bone, thus minimizing the risk of osteonecrosis after surgery.

Soft tissue dissection starts at the upper lip. The orbicularis oris muscle is transected and the superior labial artery is ligated and divided. As the dissection is continued superiorly, part of the levator labii superioris muscle is divided. The skin at the pyriform aperture is then incised; it is important to preserve a 2- to 3-mm rim of skin from the edge of the bony aperture to allow subsequent closure. The dissection is carried out until the inferior edge of the nasal bone is exposed.

The lower eyelid skin is separated from the underlying orbicularis occuli muscle by sharp dissection. The infraorbital nerve, which is located about 1 cm inferior to the infraorbital rim,24 is identified and divided. The infraorbital foramen marks the level of the horizontal osteotomy across the maxillary bone. After defining the line of osteotomy at the body of the zygoma and the premaxillary region, the osteotomy sites are preplated at these regions using titanium miniplates, allowing restoration of the preoperative dental occlusion after the return of the maxilla on completion of surgery. The titanium plates and screws are then removed and saved for subsequent use.

At the hard palate, the curvilinear mucosal incision is made down to the underlying bone. The palatal mucosal flap is elevated at the subperiosteal plane until the midline is reached (Fig. 17.5). Care must be taken, especially in patients who have torus palatinus, in whom the overlying mucosa is usually thin and thus is prone to perforation during the palatal flap dissection, increasing the risk of subsequent palatal fistula formation after surgery. The greater palatine vessels are ligated and divided to allow a complete mobilization of the palatal flap. Posterior to the last molar tooth, soft tissue is dissected until the maxillary tuberosity is exposed. The soft palate musculature is then separated from the posterior border of the ipsilateral hard palate until the midline is reached.