Tumours of the nasopharynx Introduction

J.K.C. Chan B.Z. Pilch T.T. Kuo B.M. Wenig A.W.M. Lee

Squamous Cell The Nose

Fig. 2.1 Sagittal section of the head showing the nasopharynx, nasal cavity and paranasal sinuses. {3797} 1 - Sphenoidal sinus; 2 - Superior meatus; 3- Middle meatus; 4 - Tubal elevation; 5 - Pharyngeal tonsil; 6 -Pharyngeal orifice of Eustachian tube; 7 - Salpingopharyngeal fold; 8 - Pharyngeal recess; 9 - Soft palate; 10- Uvula; 11- Frontal sinus; 12 - Sphenoethmoidal recess; 13 - Superior nasal concha; 14 - Middle nasal concha; 15 - Inferior nasal concha; 16 - Vestibule; 17 - Inferior meatus; 18 - Hard palate; 24 - Atrium.

Fig. 2.1 Sagittal section of the head showing the nasopharynx, nasal cavity and paranasal sinuses. {3797} 1 - Sphenoidal sinus; 2 - Superior meatus; 3- Middle meatus; 4 - Tubal elevation; 5 - Pharyngeal tonsil; 6 -Pharyngeal orifice of Eustachian tube; 7 - Salpingopharyngeal fold; 8 - Pharyngeal recess; 9 - Soft palate; 10- Uvula; 11- Frontal sinus; 12 - Sphenoethmoidal recess; 13 - Superior nasal concha; 14 - Middle nasal concha; 15 - Inferior nasal concha; 16 - Vestibule; 17 - Inferior meatus; 18 - Hard palate; 24 - Atrium.

The most common type of nasopharyngeal tumour is nasopharyngeal carcinoma, which is remarkable for the striking geographic differences in its incidence as well as the near consistent association with the Epstein-Barr virus (EBV). Nasopharyngeal carcinoma is also the prototype of a family of morphologically distinctive tumours - the lymphoepithelial carcinomas - that can arise in a variety of sites, such as other head and neck mucosal sites, salivary gland, lung and thymus, albeit uncommonly. Interestingly, in contrast to nasopharyngeal carcinoma, lymphoepithelial carcinomas occurring in these sites usually show a strong association with EBV only in Asians, but not in Caucasians.

Besides nasopharyngeal carcinoma, a broad range of neoplasms can arise in the nasopharynx, from epithelial to lymphoid, mesenchymal and neurogenic. Rarely, tumours derived from embryonic remnants either entrapped in their normal pathway of ascent or descent (ectopic pituitary tumour, craniopharyn-gioma) or dissociated from their normal regulatory influences (germ cell tumour) can occur. Since the nasopharynx is in close proximity to many different anatomic structures, tumours arising in the latter sites can also present clinically as a nasopharyngeal mass, for example, chordoma arising in the clivus.

Anatomy

The nasopharynx is the narrow tubular passage behind the nasal cavity. Its sloping roof and posterior wall are formed by the basi-sphenoid, basi-occiput and the first cervical vertebra. Anteriorly, it communicates with the nasal cavity via the choanae. The orifices of Eustachian tubes are in the lateral walls, and each is shielded superiorly and posteriorly by a comma-shaped elevation called the torus tubarius. Immediately above and behind the torus tubarius is a pharyngeal recess called the fossa of Rosenmuller. The nasopharynx tapers inferiorly, and continues as the oropharynx from the level of the soft palate.

The nasopharynx constitutes part of the Waldeyer ring. Histologically, its mucosa is covered by respiratory-type ciliated epithelium, but variable amounts of squamous epithelium are common. The mucosa exhibits invaginations, forming crypts that abut the underlying stroma. The stroma is rich in lymphoid tissue that often includes reactive lymphoid follicles. The surface or crypt epithelium is commonly infiltrated by many small lymphoid cells, which expand and disrupt the epithelium to produce a reticulated pattern. Some seromucinous glands are present, but they are not as abundant as in the nasal mucosa.

Clinical features

Diagnostic procedures

Various imaging techniques, such as computed tomography and magnetic resonance imaging, are helpful for detection of the presence of a tumour, as well as in precise delineation of the extent of disease. Endoscopic examination with directed biopsy is the key in obtaining materials for a definitive histological diagnosis.

Tumour staging

The TNM staging system for nasopha-ryngeal tumours (see preceding section) is only applicable for epithelial tumours, and in fact has been developed specifically for nasopharyngeal carcinoma. For lymphomas, the Ann Arbor staging system is recommended {947}.

Classification of nasopharyngeal carcinomas

In the 1978 WHO classification, three his-tological subtypes of nasopharyngeal carcinoma were recognized: squamous cell carcinoma (WHO type 1), nonkera-tinizing carcinoma (WHO type 2), and undifferentiated carcinoma (WHO type 3) {2320}. In the 1991 WHO classification, the squamous cell carcinoma subtype (keratinizing squamous cell carcinoma) was retained, while the last two subtypes in the previous classification were combined under a single category of "nonkeratinizing carcinoma", which was further subdivided as being "differentiated" or "undifferentiated"; lymphoepithe-lioma-like carcinoma was considered a morphologic variant of undifferentiated carcinoma {2317}. The use of numerical designation of WHO types 1, 2 and 3 was eliminated. The wide ranging reported figures on the frequencies of various subtypes indicate that the boundaries between the categories are not always clear (such as less well differentiated forms of keratinizing squamous cell carcinoma versus nonkeratinizing carcinoma, and nonkeratinizing carcinoma versus undifferentiated carcinoma), sampling error is a significant problem due to the small size of the biopsies, and intra-and inter-observer reproducibility of the classification is sub-optimal {323,2318, 2497,2735}. In fact, squamous cell carcinoma and nonkeratinizing carcinoma have been viewed by some investigators as being merely variants of a fairly homogeneous group of tumours {2318,2577}. Notwithstanding these problems, the proportion of keratinizing squamous cell carcinoma among all nasopharyngeal carcinomas is probably higher in low-incidence compared with high-incidence areas.

The current WHO classification maintains the terminology of the 1991 classification, with the addition of one category: basaloid squamous cell carcinoma.

Globocan Global Top Cancer Type
Fig. 2.1A Global incidence rates of cancer of the nasopharynx (all ages) in males. Age-standardized rates (ASR, world standard population) per 100,000 population and year. From: Globocan 2002 (http://www-depdb.iarc.fr/globocan/GLOBOframe.htm).

Nasopharyngeal carcinoma

Definition

A carcinoma arising in the nasopharyn-geal mucosa that shows light microscopic or ultrastructural evidence of squa-mous differentiation. It encompasses squamous cell carcinoma, nonkeratiniz-ing carcinoma (differentiated or undifferentiated) and basaloid squamous cell carcinoma. Adenocarcinoma and salivary gland-type carcinoma are excluded.

ICD-O codes

Nonkeratinizing carcinoma

8072/3

Keratinizing squamous cell carcinoma

8071/3

Basaloid squamous cell carcinoma

8083/3

Synonyms

Lymphoepithelioma, lymphoepithelioma-like carcinoma, lymphoepithelial carcinoma, Schmincke type lymphoepithelioma, Regaud type lymphoepithelioma, transitional cell carcinoma, intermediate cell carcinoma, anaplastic carcinoma, undifferentiated carcinoma with lymphoid stroma, vesicular nucleus cell carcinoma, squamous cell carcinoma (WHO-1), nonkeratinizing carcinoma (WHO-2), undifferentiated carcinoma (WHO-3).

Epidemiology

Global incidence and mortality

Nasopharyngeal carcinoma (NPC) shows a distinct racial and geographical distribution and a multifactorial etiology. Globally, there were approximately 65,000 new cases and 38,000 deaths in the year 2000 {730}. While rare in most parts of the world (onset rates commonly <1 per 105, or 0.6% of all cancers), there are certain populations for which the incidence is considerably higher, notably native and foreign-born Chinese, Southeast Asians (e.g. in Thailand, Philippines, and Vietnam), North Africans (e.g. in Algeria and Morocco), as well as native peoples of the Arctic region (e.g. in Canada and Alaska). Within these populations, there is a remarkable heterogeneity among ethnic lines {2872}. The highest incidence of NPC has long been observed in Hong Kong, where 1 in 40 men develop NPC before the age of 75 years {1981}.

Age and sex distribution

In high-risk groups, NPC incidence rises after the age of 30 years and peaks at 40-60 years, and thereafter declines {730}. The age distribution is similar in males and females, although rates in men are commonly 2-3-fold those observed in women {1981}.

Nasopharynx Examination

Fig. 2.2 Nasopharyngeal carcinoma. A and B Magnetic resonance imaging (MRI) of nasopharyngeal carcinoma (NPC): A 40-year old female patient presented with 2 months history of tinnitus, followed by neck masses, nasal symptoms, headache and diplopia. Physical examination showed left VI nerve palsy and bilateral upper-mid cervical lymph nodes. Endoscopy revealed tumour in the nasopharynx extending to posterior nasal cavity. Biopsy confirmed undifferentiated carcinoma. MRI showed NPC with extensive local infiltration of adjacent soft tissues, erosion of skull base / paranasal sinuses, and intracranial extension, together with bilateral retropharyngeal and cervical nodes.

Fig. 2.2 Nasopharyngeal carcinoma. A and B Magnetic resonance imaging (MRI) of nasopharyngeal carcinoma (NPC): A 40-year old female patient presented with 2 months history of tinnitus, followed by neck masses, nasal symptoms, headache and diplopia. Physical examination showed left VI nerve palsy and bilateral upper-mid cervical lymph nodes. Endoscopy revealed tumour in the nasopharynx extending to posterior nasal cavity. Biopsy confirmed undifferentiated carcinoma. MRI showed NPC with extensive local infiltration of adjacent soft tissues, erosion of skull base / paranasal sinuses, and intracranial extension, together with bilateral retropharyngeal and cervical nodes.

J.K.C. Chan

B.Z. Pilch

F. Bray

B.M. Wenig

P. McCarron

D. Huang

W. Foo

K.W. Lo

A.W.M. Lee

Y.X. Zeng

T. Yip

W.H. Jia

T.T. Kuo

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