Each is lined with tissue called the mucosa, which secretes mucus continuously along hairy cells called cilia and out a tiny passageway called an ostium, through which the mucus drains into the nasal cavity and down the back of the throat, where it is swallowed (unless you blow your nose).

FORBES: Balloon Therapy

They ended up producing a flexible catheter tube that goes a bit of the way up the nostrils, then a guide wire is inserted into the targeted sinus. (In live patients this is done via an endoscope and fluoroscope.) A balloon catheter is advanced over the guide wire and positioned against the blocked ostium.

FORBES: Balloon Therapy