Info

supraclavicular fossa

12%

Cranial nerve palsy

10%

Deafness

3%

Dermatomyositis

1%

Environmental factors

Diet

In high incidence regions, high levels of volatile nitrosamines in preserved food have been implicated as the putative carcinogen for NPC development {2063}. In the 1960s, it was proposed that the increased incidence of NPC among Hong Kong boat dwellers compared to house dwellers may have been due to their staple diet of salted fish {1108}. From case-control studies on Chinese, consumption of Cantonese-style salted fish in the weaning period carries odds ratios ranging from 2-7.5 {2869,2870, 2913}. Animals fed salted fish may develop nasal tumours {1142,2871, 2913}. Other preserved or fermented foods in high incidence regions, consumed during weaning and early childhood, have also been incriminated as risk factors {2869,2903}. The importance of exposure in early life is supported by two studies showing that low-risk ethnic groups born in high-risk areas also have higher risk of NPC {1212,1213}. In low incidence regions like Northern China, the consumption of salted fish still carries an adjusted relative risk as high as 5.6 {304}.

Other environmental risk factors

Other purported risk factors include cigarette smoking {1900,2868,2875}, occupational exposure to smoke, chemical fumes and dusts, formaldehyde exposure {74,1090}, and prior radiation exposure {403}.

Localization

The most common site of origin is the lateral wall of the nasopharynx, especially the fossa of Rosenm├╝ller, followed by the superior posterior wall. Cervical lymph node metastasis is a common occurrence.

Clinical features

Signs and symptoms

About half of the patients have multiple symptoms, but 10% are asymptomatic. Painless enlargement of upper cervical lymph node(s) is the most common presenting feature. Nearly half of the patients complain of nasal symptom(s), particularly blood stained post-nasal drip. Symptoms related to Eustachian tube obstruction (such as serous otitis media) also commonly occur. Headache and symptoms related to cranial nerve involvement are features of more advanced disease.

In endemic areas, NPC is an important underlying malignancy in patients presenting with dermatomyositis, being found in 12% of patients {2005} although only 1% of patients with NPC have der-matomyositis {2573}.

Imaging

Magnetic resonance (MR) is the study of choice for assessing the loco-regional extent because of its superior sensitivity and multiplanar capability. Although CT is useful in depicting cortical bone erosion, MR is superior in revealing soft tissue infiltration and intracranial extension {442,1880} as well as marrow replacement permitting early recognition of bony involvement {442,1880}. Systemic imaging workup for patients with high metastatic risk include X-ray/CT of chest, ultrasonography/CT of liver, isotope bone scan and positron emission tomography coupled with CT (PET-CT).

Table 2.03 Structures involved by local infiltration of nasopharyngeal carcinoma at presentation. Source: Magnetic resonance studies of 308 patients from Pamela Youde Nethersole Eastern Hospital, Hong Kong.

Structures involved Frequency

Adjacent soft tissues

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