Paranasal sinuses

Classification and topography of the sinuses

Four groups of paranasal (accessory) sinuses are distinguished in the cranial bones:

• Maxillary sinuses (sinus maxillares). The largest in volume; their size gradually increases depending on age (from 1–3 months to 7–12 years).
• Frontal sinuses (sinus frontales). Located within the squama of the frontal bone, typically above the supraorbital margin (margo supraorbitalis). Separated by a septum (septum sinuum frontalium); their shape and size vary individually.
• Sphenoid sinuses (sinus sphenoidales).
• Ethmoidal sinuses (ethmoidal labyrinth cells, labyrinthus ethmoidalis).

Communications with the nasal meatuses

The sinuses open into the nasal meatuses via natural ostia. The narrowness of these openings plays a major role in the development of inflammation: when the mucous membrane swells, mucus drainage is blocked, causing stasis and the formation of sinusitis.

• Superior nasal meatus (meatus nasi superior): receives the posterior ethmoidal cells and the sphenoid sinus (via the apertura sinus sphenoidalis).
• Middle nasal meatus (meatus nasi medius): receives the majority of the sinuses. Through the semilunar hiatus (hiatus semilunaris) and its posterior funnel-shaped extension — the ethmoidal infundibulum (infundibulum ethmoidale) — open the frontal sinus (anteriorly and superiorly), the maxillary sinus (posteriorly and inferiorly), as well as the anterior and some of the middle ethmoidal labyrinth cells.
• Inferior nasal meatus (meatus nasi inferior): has no connection with the sinuses; only the nasolacrimal duct (canalis nasolacrimalis) opens into it.

Osteomeatal complex and middle nasal meatus

The middle nasal meatus is of paramount clinical importance. Physicians refer to it as "the mirror of the paranasal sinuses" because purulent or catarrhal pathological processes in the sinuses manifest with characteristic discharge specifically within this meatus.

Located in this region is the osteomeatal complex — a system of anatomical structures whose knowledge is absolutely essential for modern endoscopic sinus surgery. It includes:

1. Uncinate process (processus uncinatus). It covers the natural ostium of the maxillary sinus, making it impossible to visualize during standard rhinoscopy.
2. Agger nasi cells (agger nasi).
3. Ethmoid bulla (bulla ethmoidalis), located posteriorly.
4. Lateral surface of the middle nasal concha.

Clinical anatomy of the maxillary sinus

The anterior wall of the maxillary sinus is formed by relatively dense spongy bone. During surgical interventions in this zone, there is a risk of persistent bone hemorrhage.

Key landmarks of the anterior wall:

• Infraorbital foramen: opens approximately 0.5–1 cm below the orbital margin. Contains the neurovascular bundle (maxillary nerve — n. maxillaris, along with the infraorbital artery and vein).
• Canine fossa (fossa canina): a pronounced depression below the infraorbital foramen at the level of the second premolar. It is the recommended site for surgical trepanation of the sinus.

Inflammatory diseases (sinusitis)

Inflammatory processes in the paranasal sinuses are collectively termed sinusitis. Nomenclature strictly depends on the anatomical localization of the inflammation:

• Maxillary sinusitis — inflammation of the maxillary sinus.
• Frontal sinusitis — inflammation of the frontal sinus.
• Ethmoiditis — inflammation of the ethmoidal labyrinth cells.
• Sphenoiditis — inflammation of the sphenoid sinus.

Frequently, multiple sinuses are involved simultaneously, which is termed polysinusitis. If all sinuses on only one side (right or left) are affected, it is referred to as hemisinusitis, while total bilateral inflammation of all sinuses is called pansinusitis.

Other nasal cavity communications and specific infections

In addition to the sinuses, the nasal cavity has several other important communications that determine the pathways of infection spread. Through the sphenopalatine foramen (foramen sphenopalatinum), it communicates with the pterygopalatine fossa, and through the incisive canals of the floor, with the oral cavity. The anterior and posterior ethmoidal foramina, as well as the cecal foramen of the frontal bone, connect the nasal cavity with the orbit and the anterior cranial fossa.

Specific processes may also develop in the nasal cavity, for example, in syphilis. Secondary syphilis manifests with papules, while tertiary syphilis presents with typical gummas in the mucous membrane, periosteum, bone tissue, and cartilage. The pathological process causes bone necrosis with sequestration. In the tertiary stage, consultation with a dermatologist-venereologist, blood tests (Wasserman reaction), and specific treatment are mandatory.

Class and exam questions

What else to study on this topic

• Topography of the openings of the ethmoidal infundibulum and semilunar hiatus
• Pathways of infection spread from the nasal cavity to the cranial cavity and orbit
• Age-related dynamics of development and volume increase of the maxillary sinus
• Specific nasal lesions: manifestations and management tactics in tertiary syphilis
• Anatomy and contents of the infraorbital canal

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.