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ANATOMY

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The nasopharynx is the anatomical region bounded by the sphenoid bone superiorly, the soft palate inferiorly, the clivus and uppermost cervical vertebrae posteriorly, and the nasal choanae anteriorly. The lateral walls include the mucosa covering the torus tubarius, which forms the eustachian tube orifice, and the fossa of Rosenmüller, a recess that lies posterior to the torus. The eustachian tube pierces the pharyngobasilar fascia at the sinus of Morgagni, a common site for tumor infiltration. The American Joint Committee on Cancer (AJCC) defines three anatomic spaces that are in close proximity to the nasopharynx and are relevant for staging of nasopharyngeal carcinoma (NPC): the parapharyngeal space, the carotid space, and the masticator space.1 The parapharyngeal space lies lateral and posterior to the nasopharynx. It extends from the skull base down to the level of the angle of the mandible, and is anterior to the styloid process and medial to the masticator space. The carotid space is an enclosed fascial space that lies posterior to the styloid process and contains the internal carotid artery, internal jugular vein, and cranial nerves IX–XII. The masticator space includes the muscles of mastication and is enclosed by the superficial layer of the deep cervical fascia.

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PATTERNS OF SPREAD

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The lateral nasopharyngeal wall, namely the fossa of Rosenmüller, is the most common site of origin for NPC. Lateral and posterior spread into the parapharyngeal space occurs early, while invasion of the pterygoid muscles and plates occurs in more advanced disease. The degree of parapharyngeal extension has been correlated with overall survival.2 Direct tumor extension or lateral retropharyngeal lymph node metastases in the parapharyngeal space can lead to compression or invasion of several cranial nerves, including cranial nerve XII as it exits through the hypoglossal canal, cranial nerves IX to XI as they exit from the jugular foramen, and the cervical sympathetic nerves. Compression or direct invasion of the internal carotid artery can also occur in advanced disease. Anterior spread to the nasal cavity and inferior spread to the oropharynx are common and have comparable outcomes to tumor confined to the nasopharynx.3,4 In advanced cases, tumor may spread to adjacent maxillary or ethmoid sinuses. Tumor can also involve the orbital apex through the inferior orbital fissure or invade the C1 vertebral body posteriorly and inferiorly. Superiorly, tumor can invade directly through the base of skull, sphenoid sinus, and clivus. Tumor spread through the foramen lacerum provides easy access to the cavernous sinus and can lead to the involvement of cranial nerves III to VI. Perineural spread along the maxillary and mandibular branches of the trigeminal nerve can lead to intracranial extension from spread through the foramina rotundum and ovale, respectively.

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The nasopharynx has a rich supply of submucosal lymphatics and has a high incidence of node involvement. At presentation, 90% of patients have clinically involved neck nodes; bilateral spread occurs in about 50% of ...

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