Table 3. NBI classification of nasopharyngeal mucosal microvessel patterns.

Type	IPCLs	Microvascular network	The submucosal veins
Type I	Invisible	Oblique and arborescent vessels and can be observed as thin, short brownish line shapes	Indistinct, dark-green stump shapes
Type II	Invisible	Oblique and arborescent vessels can be observed indistinctly and nearly disappear	Invisible
Type III	Invisible	Oblique and arborescent vessels which are engorged and can be seen clearly as fine brownish lines	Enlarged and can be seen clearly as thick, twisted, dark-green line shapes
Type IV	Visible, with a relatively regular arrangement and high density, appear as scattered, small, dark-brown dots.	Nearly invisible	Nearly invisible
Type V	Dilated, elongated, and distorted, and appear clearly as irregular, twisted, brownish line shapes; have snake-like, earthworm-like, or branch-like shapes.	Nearly invisible	Nearly invisible

NBI, narrow-band imaging; IPCLs, Intrapapillary capillary loops.