Paranasal Sinuses

Author: Scott A. Sheffield MS

Last update: May 22nd, 2023

Introduction to the Paranasal Sinuses:

The paranasal sinuses are cavities in the bones of the face and cranium.

• These air – filled spaces vary in size and are lined by mucous membrane.
• The mucous secretions drain into the nasal cavity and help, warm, humidify, and clean the air.
• The paranasal sinuses also help lighten the skull and resonate the voice.

Anterior View:

1. Frontal sinuses – two cavities located just above the orbits and behind the superciliary arches. [Anterior view]

• Mucous secretions are drained from each sinus by a frontonasal duct, which empties into the nasal cavity at the middle meatus.

Coronal View:

1. Ethmoid sinuses – a collection of small cavities located between the orbits in the lateral masses (or labyrinths) of the ethmoid bone. [Coronal view]

• Each lateral mass contains approximately 6 to 12 cavities, which are referred to as ethmoid air cells.
• The mucous secretions produced by the air cells drain into the nasal cavity at the superior and middle meatuses.

Have you been making any of these common anatomy learning mistakes?

2. Maxillary sinuses – two large, cavities located in the body of the maxillary bone, on either side of the nasal cavity. [Coronal view]

• Mucous produced by each sinus drains into the mid-lateral wall of the nasal cavity.

Sagittal View:

1. Sphenoid sinuses – two cavities (right & left) in the centre (or body) of the sphenoid bone. [Sagittal view]

• A thin bony septum separates the two sinuses.
• Mucous from the sinuses drains into the spheno-ethmoidal recess located at the top of the nasal cavity.

2. Frontal sinuses – two cavities located just above the orbits and behind the superciliary arches. [Sagittal view]

• Mucous secretions are drained from each sinus by a frontonasal duct, which empties into the nasal cavity at the middle meatus.

Paranasal Sinuses and Sinusitis

Several open, air-filled chambers called paranasal sinuses (see the image below) are present in the bones surrounding the nasal cavity.

Two frontal sinuses are in the bones just above the orbits, and several small ethmoid air cells (or sinuses) are in the bones between the orbits. Two large maxillary sinuses are in the cheek bones, and and two sphenoid sinuses  are in the bones at the base of the skull.

A thin layer of respiratory mucosa(or nasal mucosa) lines the paranasal sinuses. Mucus produced in the sinuses normally drains out of small apertures (or ostia) and adds to the mucus in the nasal cavity.

Struggling to learn so much new information? Find out how active recall can help you learn and remember more efficiently.

The open sinuses also help lighten the skull and resonate the voice sounds.

Sinusitis most often occurs when infections, allergies, or tissue irritants cause the sinus mucosa to become inflamed. The edematous (= swollen) membranes block the ostia drainageways that lead to the nasal cavity and mucus accumulates in the open sinus chamber.

Air trapped in the sinus is absorbed into the bloodstream, creating a negative pressure or vacuum. As the vacuum builds, so does the sense of pain. The vacuum may draw fluids into the sinus from the bloodstream. Bacteria and other microbes often grow in these fluids leading to more edema and inflammation.

Test yourself:

Anterior view [Show/Hide answers]

Test yourself:

Coronal view [Show/Hide answers]

Test yourself:

Sagittal view [Show/Hide answers]

Solidify your knowledge with this interactive quiz about the paranasal sinuses.