Table 1:

Imaging criteria for grading the nasopharynx by MRI^{^a}

MRI Grade	MRI Appearance
Grade 1 = normal	Symmetric mucosa <3 mm thick with or without small retention cysts
Grade 2 = low index of suspicion of NPC	1) Symmetric mucosal thickening >3 mm thick (marked contrast enhancement > NPC) with or without small retention cysts or a Thornwaldt cyst, or 2) symmetric enlargement of the adenoid in the central roof/upper posterior wall with a striped appearance ± a smooth band (mild contrast enhancement < NPC) extending from the roof down the posterior and lateral nasopharyngeal walls
Grade 3 = high index of suspicion of NPC	Asymmetric: asymmetry between the right and left sides of the nasopharynx in grade 1 or 2 appearance
Grade 4 = NPC	Asymmetric mucosal thickening of homogeneous intermediate signal intensity on T2-weighted images and moderate contrast enhancement on T1-weighted images (performed without fat saturation), with or without infiltration outside the nasopharynx, or a focal homogeneous enhancing mass with or without infiltration outside the nasopharynx