How many sinus cavities are there?

How many sinus cavities are there?

• A. 3
• B. 4
• C. 5
• D. 6

Answer: (B)

Sinus cavities, or paranasal sinuses, are air-filled spaces inside the skull that drain into the nasal cavity. They’re grouped by bone: frontal sinuses (in the forehead), maxillary sinuses (in the cheekbones), ethmoid sinuses (a network of small air cells between the eyes), and sphenoid sinuses (behind the eyes). Although the ethmoid region contains many tiny cells, they’re considered one sinus group. Therefore, there are four main sinus cavities in the skull. If you were counting every side separately, you might conceptually think of eight, but the standard count used in most studies is four.

Sinus cavities, or paranasal sinuses, are air-filled spaces inside the skull that drain into the nasal cavity. They’re grouped by bone: frontal sinuses (in the forehead), maxillary sinuses (in the cheekbones), ethmoid sinuses (a network of small air cells between the eyes), and sphenoid sinuses (behind the eyes). Although the ethmoid region contains many tiny cells, they’re considered one sinus group. Therefore, there are four main sinus cavities in the skull. If you were counting every side separately, you might conceptually think of eight, but the standard count used in most studies is four.