eMedicine Specialties > Radiology > Head/Neck

Nasopharynx, Squamous Cell Carcinoma

Author: Simon Lo, MBBS, Assistant Professor, Department of Radiation Oncology, Indiana University School of Medicine
Coauthor(s): Nancy Lee, MD, Consulting Staff, Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center; Sasan Karimi, MD, Assistant Professor of Radiology, Weill Medical College of Cornell University; Director of Neurospectroscopy, Director of Neuroradiology Fellowship Program, Director of Radiology at 55th Street Imaging Center, Memorial Sloan-Kettering Cancer Center; Assistant Attending Radiologist, Neuroradiology Section, Memorial Hospital for Cancer and Allied Diseases; Alan Tim-shing Choy, MBBS, FRCR(UK), FHKCR, FHKAM(Clinical Oncology), Staff Clinical Oncologist, Department of Clinical Oncology, Queen Elizabeth Hospital, Hong Kong; Sameer R Keole, MD, Staff Physician, Department of Radiation Oncology, Gershenson Radiation Oncology Center, Karmanos Cancer Institute, Harper Hospital, Wayne State University School of Medicine; J Jay Lu, MD, MBA, Consulting Staff, Director of Research, Department of Radiation Oncology, National University Hospital, The Cancer Institute, National Healthcare Group, Singapore; Kam-wang Siu, MBChB, FRCR (UK), FHKCR, Associate Consultant, Department of Diagnostic Radiology and Imaging, Queen Elizabeth Hospital, Hong Kong; Lawrence Chun-kuen Chow, MBChB, FRCSEd (ORL), FHKCORL, Associate Consultant in Otorhinolaryngology, Department of Surgery, Section of Otolaryngology, Queen Mary Hospital, Hong Kong; Vivek Sehgal, MD, Assistant Professor of Radiology, Wayne State University; Director of Magnetic Resonance Imaging, Department of Radiology, Harper University Hospital; Harold E Kim, MD, Assistant Professor, Department of Radiation Oncology, Wayne State University School of Medicine; Clinical Chief, DMC-Crittenton Radiation Oncology Center, Harper Hospital; Arthur J Frazier, MD, Assistant Professor of Radiation Oncology, Residency Program Director, Wayne State University School of Medicine; Radiation Oncologist, Barbara Ann Karmanos Cancer Institute, Gershenson Radiation Oncology Center, Harper Hospital/DMC
Contributor Information and Disclosures

Updated: Feb 12, 2009

Introduction

Background

Nasopharyngeal carcinoma (NPC) is uncommon in the United States and in most countries of the world. Although NPC accounts for less than 1% of all cancers in Americans, it is common among Southeast Asians, especially in Chinese persons from the southern provinces of Kwantung, Kwangsi, and Fukien. Native populations in Canada, Alaska, Greenland, and Africa also have elevated rates compared with those of the rest of the world.

Current epidemiologic and experimental data suggest at least 3 major etiologic factors, namely, viral, environmental, and genetic.

For excellent patient education resources, visit eMedicine's Cancer and Tumors Center. Also, see eMedicine's patient education articles Cancer of the Mouth and Throat and Skin Cancer.

Pathophysiology

Patients with locally advanced disease have poor treatment outcomes after definitive radiotherapy, especially patients with cervical lymph nodes that clinically test positive, those with cranial nerve (CN) involvement, and those with invasion of the skull base. These patients often develop distant metastases despite control of locoregional disease. Most recurrences occur within 5 years of diagnosis, but late relapses are possible. The incidence of second primary malignancy in patients with nasopharyngeal carcinoma (NPC) appears to be less than that of other head and neck cancers, which are usually related to smoking.

Tumor invasion into the skull base occurs in approximately 25% of cases and may lead to cranial nerve (CN) deficit. CN V and CN VI are most commonly involved, followed by CN III and CN IV. Patients with this involvement present with changes in ocular motion.

Unlike malignancies of the oral cavity and oropharynx, NPCs often metastasize to level V lymph nodes. Bilateral metastases are common (with rates as high as 50%) on presentation.

The Epstein-Barr virus (EBV) is associated with NPC. Titers of EBV antibodies can be elevated in patients with NPC, regardless of their ethnic and/or geographic origin. The EBV genome has been demonstrated by using nucleic acid hybridization in biopsy specimens from NPC lesions. Compared with other head and neck cancers, NPCs have high EBV antibody titers and an overexpression of the BCL2 product. Differences in the ability of the immune system to control EBV infection on the basis of the efficiency of human leukocyte antigen (HLA) haplotypes to present EBV-latent membrane protein antigen have been shown.

All NPCs are associated with EBV-latent gene products, unlike other head and neck carcinomas. About 80% of NPCs overexpress the BCL2 product. These findings are consistent and may contribute to the development of NPC by inhibiting apoptosis. Immunoglobulin A titers of EBV-replicative antigens precede the development of NPC, and they may be used as tumor markers of a response to treatment. As a result of the near-universal presence of EBV in humans, it cannot be the sole causative factor in the NPC because rates of NPC vary dramatically with geography.

Case control studies have shown an association between the consumption of salt-preserved fish at an early age and an increased risk for NPC among people from southern China. Tumor-promoting chemicals in traditional foods have been identified in areas with high rates of NPC, such as Tunisia, southern China, and Greenland. No obvious occupational exposures have been linked to NPC, though smoking increases the risk of NPC by 3 times. An inherited predisposition for NPC may exist, as evidenced in the almost 100-fold increase in incidence in a relatively homogeneous genetic group of southern Chinese individuals compared with the incidence in a comparable group of white persons.¹

Emigration does not reduce the increased risk, even into the second immigrant generation of southern Chinese in whom environmental exposures are comparable to those of other population groups. Certain HLA haplotypes occupying the short arm of chromosome 6 have been implicated. Overexpression of oncogenes has been noted, as has the overexpression of ras (76% of patients) and C -myc (90% of patients) proteins in NPC lesions. Overexpression of the C -myc protein is an adverse prognostic factor.

Despite the TP53 mutations that commonly occur in patients with other carcinomas, less than 10% of patients with NPC have mutations in the TP53 gene. Accumulation of p53 protein is often demonstrated and may be the result of a breakdown in the inactivation pathway of p53 or interference in inactivation due to the presence of viral protein or aberrant native protein. Functional inactivation may occur as a result of a homozygous deletion of the p16 (p19) gene because its product blocks normal functioning of the MDM2- induced TP53 gene function.²

Patterns of spread

NPC has common patterns of spread that are often related to the primary site. Midline tumors often spread bilaterally. As lateral tumors enlarge, they may cross the midline. Pathologic lymph nodes appear soon afterward. Tumors often grow into the lumen and extend to the orbits, maxillary sinus, nasal cavity, and soft palate. The most common route of spread is along the lymphatic pathways to the node of Rouviere. Direct extension into the retropharyngeal space, with destruction of the lateral aspect of the atlas, is possible.

Parapharyngeal invasion often results in CN impairment. Pain due to involvement of the sensory fibers of the trigeminal nerve usually precedes motor fiber involvement. When the levator veli palatini muscle is involved, the soft palate may be asymmetric at rest. Facial asymmetry result from involvement of the facial nerve is rare. Trismus occurs with direct invasion of the medial or lateral pterygoid muscles. When tumor infiltrates the pterygoid muscles, the infratemporal fossa is at risk. The maxillary sinus and orbits may be involved with invasion of the tumor from the pterygoid muscles.

Tumor may invade posteriorly to the base of the skull to involve CNs IX-XII. The sphenoid body, sphenoid sinus, greater wing of the sphenoid, foramina lacerum, ovale, and rotundum may be invaded superiorly. Downward extension of the tumor into the palate may lead to referred ear pain due to involvement of the trigeminal nerve. The parotid and submandibular glands may be invaded. The tumor may spread intracranially from the fossa of Rosenmüller and from erosion of the base of the skull.

The tumor may follow the internal carotid artery or invade through the foramen lacerum into the cavernous sinus. Symptoms from this invasion include ophthalmoplegia due to the involvement of CNs III, IV, and VI and facial numbness from involvement of the CN V. Invasion of major blood vessels may cause compressive symptoms with thrombosis or rupture. Involvement of the inner ear is uncommon but may occur with invasion of the petrous bone.

Staging

The Union Internationale Contre le Cancer (UICC) and the American Joint Committee on Cancer (AJCC) have maintained a primary tumor, regional lymph nodes, and distant metastasis (TNM) classification for NPC. However, the staging system that Ho developed is used far more frequently than the TNM system in Southeast Asia and appears to be superior.³

In 1993, the UICC and AJCC collaborated to form a task force at the international level to initiate a process of consultation with the objective of developing a relevant staging classification. The fifth edition of the TNM classification published by the UICC and AJCC in 1977 featured a complete revision of staging classification for NPC.³ The sixth edition, published in 2002, is the same as the fifth edition.

The AJCC/UICC classification system is as follows:

• Primary tumor (T)
  • TX - Primary tumor not assessable
  • T0 - No evidence of primary tumor
  • Tis - Carcinoma in situ
  • T1 - Tumor confined to the nasopharynx
  • T2 - Tumor extending to soft tissues of oropharynx and/or nasal fossa
    • T2a - Without parapharyngeal extension
    • T2b - With parapharyngeal extension
  • T3 - Tumor invading bone structures and/or paranasal sinuses
  • T4 - Tumor with intracranial extension and/or involvement of CNs, infratemporal fossa, hypopharynx, or orbit
• Regional lymph nodes (N)
  • NX - Regional lymph nodes not assessable
  • N0 - No regional lymph node metastasis
  • N1 - Unilateral metastasis in lymph node(s), 6 cm or less in greatest dimension, above the supraclavicular fossa
  • N2 - Bilateral metastasis in lymph node(s), 6 cm or less in greatest dimension, above the supraclavicular fossa
  • N3 - Metastasis in a lymph node(s)
    • N3a - Greater than 6 cm in dimension
    • N3b - Extension to the supraclavicular fossa
• Distant metastasis (M)
  • MX - Distant metastasis not assessable
  • M0 - No distant metastasis
  • M1 - Distant metastasis

AJCC/UICC stages are as follows:

• Stage 0 - Tis, N0, M0
• Stage I - T1, N0, M0
• Stage IIA - T2a, N0, M0
• Stage IIB
  • T1, N1, M0
  • T2, N1, M0
  • T2a, N1, M0
  • T2b, N0, M0
  • T2b, N1, M0
• Stage III
  • T1, N2, M0
  • T2a, N2, M0
  • T2b, N2, M0
  • T3, N0, M0
  • T3, N1, M0
  • T3, N2, M0
• Stage IVA
  • T4, N0, M0
  • T4, N1, M0
  • T4, N2, M0
• Stage IVB - Any T, N3, M0
• Stage IVC - Any T, any N, M1

Survival is consistently correlated with the stage of disease. Patients with disease in early stages fare markedly better than others, with overall survival rates of 80% for stage I and 65% for stage II. Survival rates for patients with more advanced disease are 45% in stage III and 30% in stage IV. The extension of the tumor behind the styloid process or into the masticator space is common and is associated with poor survival, with 5-year relapse-free survival rates of 46% and 43%, respectively.

Adverse prognostic features include CN palsies, involvement of the paranasopharyngeal space, advanced age, male sex, and involvement of the lymph nodes. The prognosis is worse with distal lymph node involvement proceeding from the upper cervical chain to the middle and lower cervical chain; patients with bilateral involvement have a 5-year overall survival rate of less than 10%.

Pathology

Approximately 80-99% of all malignant nasopharyngeal tumors arise from the epithelium and should be considered variants of squamous cell carcinoma. According to the World Health Organization (WHO), NPC is classified into 3 subtypes: (1) WHO type 1, or squamous cell carcinoma; (2) WHO type 2, or nonkeratinizing carcinoma; and (3) WHO type 3, or undifferentiated carcinoma.

The term lymphoepithelioma or lymphoepithelial carcinoma is used to describe nonkeratinizing and undifferentiated carcinoma with an abundant lymphoid stroma.

In North America, WHO types 1, 2, and 3, account for 20%, 10%, and 70% of all NPCs, respectively. In Hong Kong, the respective rates are 3%, 9%, and 88%.

Frequency

United States

In Hawaii, the incidence among whites is 0.7 case per 100,000 men and 0.9 case per 100,000 women. The incidence among people of Chinese descent in Hawaii is 8.9 cases per 100,000 men and 3.7 cases per 100,000 women. The incidence among people of Chinese descent in Los Angeles is 6.5 cases per 100,000 men and 3.7 cases per 100,000 women. These data were extracted from the International Agency for Research on Cancer, 1992.⁴

International

In Hong Kong, the incidence is 28.5 cases per 100,000 men and 11.2 cases per 100,000 women. In Singapore, among Chinese persons, the incidence is 18.1 cases per 100,000 men and 7.4 cases per 100,000 women. In Shanghai, the incidence is 4.0 cases per 100,000 men and 1.9 cases per 100,000 women. In Tianjin, China, the incidence is 1.8 cases per 100,000 men and 0.6 case per 100,000 women. In Miyagi, Japan, the incidence is 0.5 case per 100,000 men and 0.2 case per 100,000 women. In Manila, the Philippines, the incidence is 8.3 cases per 100,000 men and 3.4 cases per 100,000 women. In Setif, Algeria, the incidence is 5.0 cases per 100,000 men and 2.2 cases per 100,000 women. In Yorkshire, United Kingdom, the incidence is 0.2 case per 100,000 men and 0.1 case per 100,000 women. In the Northwest Territories and the Yukon, Canada, the incidence is 6.4 cases per 100,000 men and 2.3 cases per 100,000 women.⁴

Mortality/Morbidity

The 5-year survival rate after radiation therapy is 36-58%. For locally advanced disease, the 3-year overall survival rate is reported to be 78% for chemoirradiation versus 47% for radiotherapy alone.

As a result of the large treatment volume and high radiation dose required in most patients with nasopharyngeal carcinoma (NPC), various complications can occur. The overall complication rate is 31-66%. Severe complications occur in 6-15% of patients, and fatal complications occur in 1-3% of patients. Complication rates increase with concurrent chemoirradiation or coexisting medical conditions, such as hypertension or diabetes mellitus.

• Xerostomia is the most common sequela. Dental problems occur in 4-17% of patients. The use of dental topical fluorides and good dental hygiene before, during, and after radiation therapy can reduce the incidence of dental caries. Chronic otitis media occurs in 3-18% of patients after radiation therapy, and hearing loss occurs in 6-8%. The incidence of hearing impairment is related to the dose to the cochlea, and doses higher than 50 Gy significantly increase the incidence of hearing deficits.
• Trismus occurs in 5-10% of patients as a result of fibrosis and contraction of the pterygoid muscles or fibrosis of the temporomandibular joint. Patients should be advised to perform mandibular exercises to prevent the progression of trismus. Surgical intervention may be considered to relieve severe trismus. Soft tissue, bone necrosis, or both occur in 5-16% of patients.
• Brain necrosis occurs in 2-3% of patients. The incidence of cranial nerve (CN) entrapment (especially for the last 4 CNs) due to soft tissue fibrosis is approximately 1-6%. Transverse myelitis has been reported to occur in 1-4% of patients. Because a portion of the orbit, and sometimes the eye (especially in patients with advanced disease), is usually included in the clinical target volume, radiation-induced retinopathy and injury to the optic nerve can occur, causing blindness. Therefore, the daily fraction should be limited to 2 Gy or less, and the retina and optic apparatus should be shielded after 45-50 Gy to prevent this devastating complication.
• In patients who receive radiation therapy to the entire thyroid gland, the rate of hypothyroidism is increased by 30-40%. Thyroid-function testing should be done before therapy to provide a baseline and then repeated after treatment for monitoring. Hypothyroidism is highly treatable with medical approaches.

Race

The incidence of nasopharyngeal carcinoma (NPC) is highest among southern Chinese populations, particularly those originating from Kwantung province. Mixed Chinese populations of Southeast Asians and Eskimos have the next highest rates. The incidence is intermediate among people of North African or Filipino descent. NPC is rare in whites and in the Japanese population.

Sex

Nasopharyngeal carcinoma (NPC) occurs more frequently in men than in women, with a male-to-female ratio of 2-3:1. Some series have shown that the prognosis is better in women than in men, but other series have not demonstrated this difference.

Age

The mean age at presentation is 45-55 years. Younger patients appear to have survival rates better than those of older patients. In 1 series from Hong Kong, a statistically significant difference was found between the 5-year survival rates in patients younger than 40 years and patients aged 40 years or older. However, data from the Children's Cancer Study Group regarding patients younger than 30 years showed that the 5-year survival rate was 51%, which was not significantly different from those reported in other adult series.

Anatomy

The nasopharynx is a space. As the name implies, it contains 2 distinct parts: (1) the anterior upper division, which is histologically, embryologically, and morphologically related to the nasal cavity, and (2) the inferior posterior division, which is similarly related to the oral cavity, as both are foregut structures. The nasopharynx measures 2-3 cm in the anteroposterior dimension and as much as 3-4 cm in the vertical and transverse dimensions. It lies behind the nasal fossa, marked by the posterior choanae.

The base of the skull, specifically, the clivus and the first 2 vertebral bodies, form the posterior bone border. The lateral aspects of the space are flanked by the pharyngeal fascia and mucosa, which also overlies the posterior bone border. The oropharyngeal cavity is underneath it, and the soft palate demarcates the anterior inferior edge. The superior border blends with the posterior wall and houses abundant lymphoid tissue in children, which usually fades with age. If this lymph tissue (adenoid tonsils) persists into adulthood, it may be confused with tumor during examination. This space, without many natural barriers of spread or growth, has many critical structures in the immediate vicinity. The diffuse nature of this border contributes to the variety of routes of spread and multiple complaints at presentation.

Identifiable anatomic structures normally visible on examination include the eustachian tubes on the lateral walls. The cartilaginous ends of the tubes push the mucosa outward to form a ridge; the torus tubarius; and a recessed space, the fossa of Rosenmüller.

Depiction of the fossa of Rosenmüller is difficult but crucial because it is the most common site of origin in NPC. The borders of the fossa are the eustachian tube anteriorly, the levator veli palatini muscle anterolaterally, the retropharyngeal space posteriorly, the upper edge of the superior constrictor muscle inferiorly, and the tensor veli palatini muscle and pharyngeal space laterally. The superior border is the base of the skull with the foramen lacerum medially, the petrous apex and carotid canal posteriorly, and the foramina ovale and spinosum anterolaterally. These anatomic relationships provide explanations for the symptoms commonly found in patients and the pathways for direct extension.

Sensory innervation of the nasopharynx and the posterior soft palate is derived from CN IX, except for a variable area adjacent to the tubal orifices supplied by the maxillary division of CN V. Several separate small nerves of CN IX comprise the glossopharyngeal nerve, including a communicating fiber from the tympanic branch of CN IX that follows the same route as the greater petrosal nerve. The sensory pathway for the trigeminal component runs from the roof of the nasopharynx along the palatovaginal canal and past the pterygopalatine ganglion to the pterygopalatine fossa. The origin of the motor component for the pharyngeal musculature is the cranial root of the accessory nerve that courses with the vagus nerve. Further muscular innervation derives from the pharyngeal plexus, a commingling of the motor fibers of CNs IX and X.

Embryologic remnants may persist and be confused with cancer. A pharyngeal hypophysis, a vestige of the Rathke pouch (the origin of the anterior pituitary gland), may persist in the vomerosphenoidal articulation, appearing as a midline submucosal mass between the posterior border of the nasal septum and pharyngeal tonsil. Although usually small, the hypophysis may reach 10 mm. Capable of hormone production, it may hypertrophy in women undergoing menopause without hormone replacement.

Lymphatic drainage

Lymphoid tissue is abundant in the nasopharynx, as evidenced in the high rate of nodal metastases found at diagnosis. Three main groups of submucosal collecting pathways drain the pharynx, the superior, middle, and inferior pathways. The superior pathway provides the primary drainage of the nasopharynx along with a small contribution by the middle pathway. The superior pathway drains the oropharynx, soft palate, eustachian tube and fossa of Rosenmüller, tympanic cavity, and nasal fossae.

The superior pathway is divided into median and lateral groups. The median group drains the roof and posterior border of the nasopharynx into the lateral retropharyngeal node. This node may be bypassed, in which case, the first echelon node is the upper deep cervical lymph node chain located near the internal jugular vein. The lateral group drains the lateral nasopharynx, including the fossa of Rosenmüller, and flows into the lateral half of the upper internal jugular chain or into the lateral retropharyngeal node. The retropharyngeal nodes atrophy with age and usually are obliterated by adulthood. They lie in a potential space behind the posterior wall of the nasopharynx and anterior to the prevertebral fascia. The lateral group is often a single node or several confluent nodes, termed the node of Rouviere. Occasionally, the node is absent on 1 side and usually nonpalpable.

The node of Rouviere is the most commonly involved lymph node. It usually lies below the base of the skull near the level of the atlas and may overlay the internal carotid artery. The upper cervical lymph node chain encases the internal jugular vein and receives lymph from the node of Rouviere. Nodes exist at the angle of the mandible, the superior sternocleidomastoid muscle, and the apex of the posterior triangle. Nodes also course adjacent to the pathways of CNs XI and XII. The chain runs inferiorly to the anterior neck triangle where the jugulodigastric node is present, which is the most important and constant node. The efferent pathway descends along the internal jugular vein to the lower deep cervical nodes, terminating at the junction of the internal jugular vein and subclavian vein on the right and the thoracic duct on the left.

Presentation

In patients with nasopharyngeal carcinoma (NPC), the most common presentation is a neck mass representing a metastatic lymph node. Nonspecific, nonsensitive complaints include symptoms of allergic rhinosinusitis, such as nasal congestion, rhinorrhea, and epistaxis. When the eustachian tube is blocked, as often occurs with tumors in the fossa of Rosenmüller, serous otitis media, ear pain, and ipsilateral hearing loss may occur.

One function of the nasopharyngeal space is to increase the resonant quality of the voice, which may be attenuated by the mass effect of a tumor. Anterior invasion into the soft palate results in resting asymmetry of the posterior oral cavity. The Trotter triad consists of decreased hearing, mandibular pain, and impaired soft palate mobility. With invasion of the base of the skull, headaches may occur in the temporal and occipital regions. Superior invasion into the orbit may result in proptosis.

Routes into the orbit are from the posterior nasal fossa through the ethmoid air cells or tracking along the CNs into the eye from previous cavernous sinus invasion. Cavernous sinus invasion occurs because the tumor tracks through the foramen lacerum, which often leads to multiple CN deficits. The order of loss is CNs VI, III, V1, V2, and IV as the tumor invades the superior orbital fissure (CNs III, IV, V1, and VI), foramen rotundum (CN V2), and foramen ovale (CN V3.) The most common deficits are ophthalmoplegia (CN VI), ptosis (CN III), and pain and anesthesia of the supraorbital and superior maxillary regions (CN V1 followed by CN V2). Complete ophthalmoplegia occurs with CN III, IV, and VI involvement. Metastatic parapharyngeal nodes can compress the posterior CNs, namely, CNs IX, X, XI, and XII. A tumor in the fossa of Rosenmüller can directly invade these nerves because they exit the base of the skull in the parapharyngeal space.

A deficit indicating CN involvement is dysphagia from hemiparesis of the muscles innervating the superior constrictor muscles (CN IX) and soft palate (CN X). Sensory deficits in the mucous membranes of the soft palate, pharynx, and larynx result from CN X injury and dysgeusia from CN IX. CN XI injury results in atrophy and paralysis of the trapezius and sternocleidomastoid muscles, and CN XII injury results in deviation of the tongue to the side of injury, with atrophy of the muscle, causing difficulty with deglutition. Horner syndrome with ptosis, miosis, and anhydrosis occurs when the cervical sympathetic plexus coursing along the carotid is involved. NPC is more likely to extend into the cranium through the foramen lacerum or foramen ovale than invade the bone.

Preferred Examination

Preferred examinations include the following: clinical examination of the neck, fiberoptic examination, CT scanning of the nasopharynx and neck, and MRI of the nasopharynx and neck.^5,6

Pathologic diagnosis is achieved by examining biopsy specimens from the nasopharyngeal mass. Workup includes assessment of the tumor by means of flexible or rigid endoscopic examination; documentation of the extent of the tumor and the location of neck nodes; assessment of CN function, vision, and hearing; CT or MRI of the head and neck regions (see CT Scan, Findings and MRI, Findings); chest radiography; and blood work, including complete blood counts and serum chemistry panels, particularly renal function tests.

Creatinine clearance is determined by using 24-hour urine specimens. Any clinical or laboratory findings suggestive of distant metastasis warrant further investigation. Baseline endocrine function is established. Dental and oral hygiene evaluation is necessary before radiation therapy is started. MRI is often more helpful than CT in depicting abnormalities and in defining the extent of tumors.

Limitations of Techniques

Evaluation of mucosal lesions is best achieved endoscopically. Imaging findings often lead to incorrect estimates of the extent and frequency of mucosal involvement. Conversely, clinical evaluation is inadequate in tumors located entirely or almost entirely beneath the mucosa. Hence, the full staging process should include endoscopy, clinical examination of the neck, and imaging.

The role of CT is well established. CT remains the most common modality for tumor mapping and nodal staging, particularly in the regions of the globe in which nasopharyngeal carcinoma (NPC) occurs with high frequency, because access to MRI remains limited.

MRI is superior to CT in demonstrating the extent of soft tissue tumors. This is particularly relevant in tumors with extensive submucosal involvement. Generally, CT is accepted as being superior to MRI in the detection of skull base involvement; however, contrary to common belief, changes in the skull base are better identified on MRI than on CT. Although cortical erosion often is diagnosed more confidently by using CT, marrow infiltration is better determined with MRI. MRI is also more sensitive than CT in detecting perineural invasion; the obliteration of fat just external to the foramen rotundum or foramen ovale is as a good sign of early perineural infiltration.

Cervical lymphadenopathy is depicted better by using CT scans than MRIs, especially in terms of nodal necrosis and extracapsular spread. Although large amounts of data exist regarding the superiority of CT over MRI in the assessment of nodal metastasis, both modalities are adequate in routine clinical practice. Compared with MRI, CT rarely provides additional information that results in a change in treatment options.

MRI is recommended for use in staging tumor recurrences. Although MRI has limitations in separating postirradiation fibrosis from tumor recurrence, it is superior to CT in identifying submucosal infiltration, replacement of marrow in the skull base, and intracranial spread.

In many tumors that are staged with CT, their classification may be changed on MRI, especially in patients with involvement of the skull base or early CN infiltration and intracranial extension. This disparity of staging results between CT and MRI can potentially affect treatment recommendations, which may in turn pose problems in comparing treatment outcomes.

Differential Diagnoses

Other Problems to Be Considered

Malignant neoplasms

Malignant lymphoma
Plasmacytoma
Adenocarcinoma
Melanoma
Sarcoma

Benign neoplasms

Angiofibroma
Neuroma

Normal variants

Lymphoid tissue

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