Tympanostomy tube patency

Proper function of a tympanostomy tube is assured if it is seen to span the eardrum, its lumen is unobstructed, and no middle ear effusion is present.
(A) A tube that is in place and patent.
(B) A tube that is in place but occluded.
(C) A tube that is in place and patent but appears to have extruded.