LOCAL STAGING OF NASOPHARYNGEAL CARCINOMAS
Squamous cell carcinoma accounts for approximately 70% to 98%of all malignant nasopharyngeal neoplasms. Lymphomas account forabout 20% of cases, and the remaining 10% result from an array oflesions, including adenocarcinomas, cystic adenoid carcinomas,rhabdomyosarcomas, etc. Nasopharyngeal squamous cell carcinoma isa relatively rare type of cancer, accounting for 0.25% ofmalignant neoplasms in the North America, however presents a highincidence among Asians, particularly in the Southeast Asia,accounting for up to 18% of all malignancies inChina(2). It tends to affect younger age groupsthan other lesions of the upper respiratory-digestive tract, withhigher prevalence in men than inwomen(14).
Risk factors for development of nasopharyngeal carcinomainclude those for oropharinx carcinoma, like nitrosamine (presentin food seasonings) and polycyclic hydrocarbons consumption,chronic tobacco and alcohol consumption, precarious conditions oflife, repeated sinonasal infections. Additionally, there is astrong association with Epstein-Barr virus, particularly inSoutheast Asia, where the affected population usually is youngerwhen compared with the Caucasianpopulation(2).
The World Health Organization has updated the histologicalclassification of nasopharyngeal carcinomas, dividing them intotwo large subtypes: 1 – squamous cell carcinoma, and 2 –non-keratinized carcinoma.
The non-keratinized carcinoma subtype is still subdividedinto: subtype I – differentiated (2a) and II – undifferentiated(2b). The term lymphoepithelioma also is utilized to designatethese two subtypes of tumors. These new nomenclatures 2a and 2bcorrespond, respectively, to 2 and 3 types in the formerclassification(2). The latest one,undifferentiated subtype of non-keratinized, seems to be moreclosely related to the presence of Epstein-Barr virus, resultingin the development of cancer in younger patients, by a stillunknown mechanism(15–17). Yet, the presence ofthe viral genome (Epstein-Barr virus) in metastatic lymph nodesmight suggest a nasopharyngeal carcinoma as primarysite(18).
The site of origin varies. Most common sites are the lateral nasopharyngeal walls, most frequently the lateral pharyngeal recess. Frequently the torus tubarius is involved(14,19,20) (Figures 5A and 5B).
The nasopharyngeal carcinoma clinical manifestation depends onthe size, localization and tumor dissemination route. Usually,small lesions are asymptomatic, but serous otitis media,headache, nasal obstruction, epistaxis, "throat ache", trismus,and proptosis may be present, depending on the degree ofinvolvement of neighbor structures and the size of thelesion(2). Other less frequent symptoms may bepresent: hemotympanum, periauricular mass, plugged ear sensation,barotrauma, polyp inside the inner ear, and sudden,neurosensorial hearing loss(21).
Specific anatomical routes through which the tumordisseminates to the skull base or intracranial regions, as wellas the lymph node or distant metastatic dissemination are foundon CT and MRI images.
Nasopharyngeal carcinoma is one of few head and neck tumorswhich do not present any relationship between the tumor size andthe presence of lymph node metastasis, and this is due to thewide drainage plexus present in the region. About 90% of casespresent with lymph node metastasis at the moment of diagnosis,and 50% of them already present bilateraldisease(17).
The primary drainage site is to retropharyngeal lymph nodes,but, since in the adulthood these lymph nodes may presentobliteration by inflammatory/infectious processes occurred in thechildhood, they may not be involved. Other preferential drainagesites are the II, III, and, occasionally, Vlevels(2).
Distant metastasis may affect the lungs, sketeleton, liver,and, occasionally, the choroid plexus(17).
Usually, nasopharyngeal carcinomas disseminate through themucosa and sub-mucosa alongside muscular clusters, and in theirorigins and insertions, adjacent to fat planes surrounding themuscles, along the vascular/nervous bundles, and through theforamens created for the normal passage of these structures. Somestructures, like the auditory tube cartilaginous portion andpharyngobasilar fascia, demonstrate higher resistance against thetumor invasion(2, 19,22,23).
The perineural dissemination is the most insidious form oftumor dissemination, and its presence is extremely important forthe prognosis and therapeutical planning. The nerve of thepterygoid canal represents the main nasopharyngeal carcinomaperineural dissemination route. Perineural dissemination shouldbe suspected in case of abnormal enlargement or enhancement ofthe nerve with obliteration of fatplanes(24).
The nasopharyngeal carcinoma frequently originates in thelateral pharyngeal recess region. On CT images, asymmetry,blurring or obliterations are usually seen, and may be associatedwith an increase of the levatorpalati(6,19,25).
When the tumor surpasses the pharyngobasilar fascia, itinvades the parapharyngeal space; according to Hoe, this occursin 65% of nasopharyngeal carcinomas(14,25).Sham and Choy have found 85% involvement of thisregion(26). From the parapharyngeal space, thetumor may extend superiorly, anteriorly, laterally orposteriorly.
The superior extension of the nasopharyngeal carcinoma is the most frequent route of direct dissemination (48%)(19,25). Intracranial extension may occur by direct destruction of the skull base or by extension towards the sinus cavernosum via the foramen lacerum or foramen ovale. The superior extension of the tumor is visualized as an infiltration of sphenoid sinus with opacification or presence of fluid and bone destruction. Most usually, areas of bone destruction in the skull base are the clivus, the foramen lacerum and the middle cranial fossa, around the sphenoid sinus floor and foramen jugularis (Figure 6).

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Mailing Address:Dra. Ilka YamashiroRua Afonso Celso, 1637, ap. 33, Chácara InglesaSão Paulo, SP,
Received October 28, 2004.Accepted after revision March 17, 2005.


* Study developed at Service of Diagnostic Imaging – Hospital Heliópolis Department of Radiology, São Paulo, SP, Brazil.

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