Antrochoanal polyp opens In which meant
ANTROCHOANAL POLYP most commonly seen in children.

They are unilateral, usually arises from the mucosa of maxillary antrum near its accessory ostium comes out of it & grows in the channel & nasal cavity.

Maxillary sinus opens into the middle meatus.
Middle meatus
Superior meatus
Inferior meatus
Sphenoethmoidal recess