Hypoplasia of maxillary sinus is uncommon and as it is asymptomatic it is usually identified as an incidental finding when CT is obtained for other reasons. 

Bolger described a classification of maxillary sinus hypoplasia in 1990 as follows:

• Type I
  • mild hypoplasia
  • normally developed uncinate process
  • well developed infundibulum
• Type II
  • significant hypoplasia
  • hypoplastic / absent uncinate process
  • poorly defined or absent infundibulum
• Type III
  • profound hypoplasia
  • absent uncinate process