Why antrochoanal polyp grows posteriorly?

Antrochoanal polyp Click on image for an enlarged view

• Antrochoanal polyp arises from the maxillary sinus.
• It usually grows posteriorly towards the nasopharynx

The reasons for growing posteriorly are as follows:

• Mucociliary flow is directed posteriorly
• Accessory ostium, through which the antrochoanal polyp comes out is located more posterior in the nasal cavity
• Effect of gravity when lying down
• Inspiratory airflow is stronger compared to expiratory flow
• Broetz anatomical variation theory
• Bernoulli effect

Image credits:

Antrochoanal polyp – Otolaryngology Houston
Antrochoanal polyp – endoscopic view – Otolaryngology Houston
Antrochoanal polyp CT scan – Radiopaedia. Original image can be viewed here