The Paranasal Sinuses - Podcast Version 0:00 / 0:00 1x 0.25x 0.5x 0.75x 1x 1.25x 1.5x 1.75x 2x The paranasal sinuses are air-filled extensions of the nasal cavity. There are four paired sinuses – named according to the bone in which they are located – maxillary, frontal, sphenoid and ethmoid. Each sinus is lined by a ciliated pseudostratified epithelium, interspersed with mucus-secreting goblet cells. The function of the paranasal sinuses is a topic of much debate. Various roles have been suggested: Lightening the weight of the head Supporting immune defence of the nasal cavity Humidifying inspired air Increasing resonance of the voice The paranasal sinuses are formed during development by the nasal cavity eroding into the surrounding bones. All the sinuses therefore drain back into the nasal cavity – openings to the paranasal sinuses can be found on the roof and lateral nasal walls. In this article, we shall look at the anatomy of the paranasal sinuses – their structure, anatomical relations and innervation. Adobe Stock, Licensed to TeachMeSeries Ltd Fig 1Location of the paranasal sinuses. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Frontal Sinuses There are two frontal sinuses located within the frontal bone of the skull. They are the most superior of the paranasal sinuses, and are triangular in shape. Drainage is via the frontonasal duct. It opens out at the hiatus semilunaris, within the middle meatus of the nasal cavity. Sensation is supplied by the supraorbital nerve (a branch of the ophthalmic nerve), and arterial supply is via the anterior ethmoidal artery (a branch of the internal carotid). Sphenoid Sinuses The sphenoid sinuses are situated within the body of the sphenoid bone. They open out into the nasal cavity in an area supero-posterior to the superior cocha – known as the spheno-ethmoidal recess. They are innervated by the posterior ethmoidal nerve (a branch of the ophthalmic nerve), and branches of the maxillary nerve. They recieve blood supply from pharyngeal branches of the maxillary arteries. Clinical Relevance Transsphenoidal Surgery The sphenoid bone shares a close anatomical relationship with the pituitary gland. Indeed, the pituitary can be accessed surgically by passing instruments through the sphenoid bone and sinus. This type of surgery is known as endoscopic trans-sphenoidal surgery (ETSS), and is the usual treatment of choice for pituitary adenomas. It allows for the surgical management of pituitary pathology without the need for a more extensive craniotomy. By TeachMeSeries Ltd (2026) Fig 2The transsphenoidal approach to pituitary surgery. Ethmoidal Sinuses There are three ethmoidal sinuses located within the ethmoid bone: Anterior – Opens onto the hiatus semilunaris (middle meatus) Middle – Opens onto the lateral wall of the middle meatus Posterior – Opens onto the lateral wall of the superior meatus They are innervated by the anterior and posterior ethmoidal branches of the nasociliary nerve and the maxillary nerve. The anterior and posterior ethmoidal arteries are responsible for arterial supply. Maxillary Sinuses The maxillary sinuses are the largest of the sinuses. They are located laterally and slightly inferiorly to the nasal cavities. They drain into the nasal cavity at the hiatus semilunaris, underneath the frontal sinus opening. This is a potential pathway for spread of infection – fluid draining from the frontal sinus can enter the maxillary sinus. By TeachMeSeries Ltd (2026) Fig 3The conchae have been removed, showing the various openings on the lateral wall of the nasal cavity. Clinical Relevance Sinusitis As the paranasal sinuses are continuous with the nasal cavity, an upper respiratory tract infection can spread to the sinuses. Infection of the sinuses causes inflammation (particularly pain and swelling) of the mucosa, and is known as sinusitis. If more than one sinus is affected, it is called pansinusitis. The maxillary nerve supplies both the maxillary sinus and maxillary teeth, and so inflammation of that sinus can present with toothache. Do you think you’re ready? Take the quiz below Pro Feature - Quiz The Paranasal Sinuses Question 1 of 2 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/2 1800 More Questions Available Upgrade to TeachMeAnatomy Pro Challenge yourself with over 1800 multiple-choice questions to reinforce learning Learn More Frequent questions What are the paranasal sinuses and their functions? The paranasal sinuses are air-filled extensions of the nasal cavity that include the maxillary, frontal, sphenoid, and ethmoid sinuses. They are thought to lighten the weight of the head, support immune defence, humidify inspired air, and enhance voice resonance. How do the frontal sinuses drain and what is their innervation? The frontal sinuses drain through the frontonasal duct into the hiatus semilunaris in the middle meatus of the nasal cavity. They receive sensory innervation from the supraorbital nerve, a branch of the ophthalmic nerve. Where are the sphenoid sinuses located and how do they open into the nasal cavity? The sphenoid sinuses are located within the body of the sphenoid bone and open into the nasal cavity at the spheno-ethmoidal recess, which is positioned supero-posterior to the superior concha. What is the clinical significance of the maxillary sinuses? The maxillary sinuses, being the largest, drain into the nasal cavity at the hiatus semilunaris, creating a potential route for infection spread. Inflammation of these sinuses can lead to sinusitis, which may also cause referred pain in the maxillary teeth. How are the ethmoidal sinuses classified and what is their arterial supply? The ethmoidal sinuses are classified into anterior, middle, and posterior groups based on their drainage points into the nasal cavity. They receive arterial supply from the anterior and posterior ethmoidal arteries, which branch from the ophthalmic artery. Rate This Article