The magnetic resonance imaging (MRI) diagnosis criteria for nasopharyngeal
carcinoma (NPC)
The MRI diagnosis criteria are mainly based on the review of King et al (World J Radiol
2010; 2(5): 159) and the American Joint Committee for Cancer (AJCC) cancer staging
manuals.
Nasal cavity involvement
Tumor crosses the margin of the choanal orifice, extends into the main body of the
nasal cavity or spread centrally along the nasal septum. Fiberoptic nasopharyngoscopy
helps to diagnosis the doubtful cases.
Oropharynx involvement
Oropharynx includes the base of the tongue, the inferior surface of the soft palate and
the uvula, the anterior and posterior tonsillar pillars, the glossotonsillar sulci, the
pharyngeal tonsils, and the lateral and posterior pharyngeal walls. But inferior superficial
extension down to the mucosa of the oropharynx is uncommon, tumors preferentially
spreading superiorly to the skull base. Therefore, invasion of the oropharynx rarely
occurs as an isolated event and is not usually an early sign of disease because it is already
associated with tumor spread to sites such as the parapharyngeal region, skull base and
cranium.
Parapharyngeal space involvement
Tumor involves lateral penetration through the levator palatini muscle and
pharyngobasilar fascia to involve the tensor palatini muscle and parapharyngeal fat space.
The anatomic parapharyngeal space contains primarily deep lobe of parotid gland, fat,
vascular structures, and small branches of the mandibular division of the fifth cranial
nerve. The vascular components include the internal maxillary artery, ascending
pharyngeal artery, and the pharyngeal venous plexus. Further posterolateral spread may
also involve the carotid space and encase the carotid artery.
Masticator space involvement
In the sixth edition of the TNM staging system (TNM6th), masticator space
involvement denotes extension of tumor beyond the anterior surface of the lateral
pterygoid muscle or lateral extension beyond the posterolateral wall of the maxillary
antrum and the pterygomaxillary fissure. In the seventh edition of the TNM staging
system (TNM7th) and the Chinese 2008 Staging System for NPC (TNMc2008),
masticator space primarily consists of the muscles of mastication. Anatomically, the
superficial layer of the deep cervical fascia splits to enclose the muscles of mastication to
enclose this space. These muscles are the medial and lateral pterygoid, masseter, and
temporalis.
Lymph nodes metastases
MRI diagnoses nodal metastases on the basis of size if the shortest nodal axial
diameter reaches 5 mm or greater in the lateral retropharyngeal region, 11 mm in the
jugulodigastric region or 10 mm in other non-retropharyngeal nodes of the neck, or if
there are a group of three or more nodes which are borderline in size. However, it should
be noted that normal nodes become progressively smaller moving caudally in the neck
and therefore a size of 5-7 mm is sometimes used as a cutoff in the lower neck. NPC
nodes are often necrotic and show extracapsular spread and these signs are used by MRI
to identify metastatic nodes irrespective of size.
The criteria of treatment failure
Treatment failure was defined as locoregional relapse, distant metastasis or death from
any cause, whichever was first. Locoregional relapses included local relapses, regional
relapses or both. All local relapses were diagnosed with fibreoptic endoscopy and
biopsy, MRI scan, or both, of the nasopharynx and the skull base showing progressive
bone erosion and soft tissue swelling. Regional relapses were diagnosed by clinical
examination of the neck and, in doubtful cases, by fine needle aspiration or an MRI
scan of the neck. Chest radiography, abdominal sonography, Technetium-99m-methylene
diphosphonate (Tc-99-MDP) whole-body bone scan and/or 18F-fluorodeoxyglucose
positron emission tomography and computed tomography (PET/CT) were used to screen
distant metastases. If metastases were suggested, then additional computed tomography
(CT), MRI, biopsy, or aspiration at the site in question was underwent to further confirm
them.