Maxillary sinus (sinus maxillaris)
The maxillary sinus is the largest of all paranasal sinuses. Visually, it resembles a four-sided pyramid and topographically extends from the level of the first premolar to the maxillary tuberosity. In clinical practice, it is important to remember that its superior wall simultaneously serves as the floor of the orbit. If this wall becomes thinned, the inflammatory process (maxillary sinusitis) can easily spread into the orbital region.
Anatomy of the walls:
- Anterior wall: formed by the part of the maxilla located between the alveolar process and the infraorbital margin. In the center it is quite thin, but thickens toward the periphery. Within the thickness of this bony structure run the alveolar arteries (aa. alveolares from the maxillary artery system) and branches of the infraorbital nerve — rr. alveolares superiores anteriores et medius (from the V2 branch of the trigeminal nerve). These nerves participate in the formation of the superior dental plexus (plexus dentalis superior).
- Posterolateral wall: formed by the maxillary tuberosity (tuber maxillae). Superiorly it borders the inferior orbital fissure, and posteriorly it reaches the pterygopalatine fossa. The posterosuperior angle of the wall is in close contact with the sphenoid sinus and ethmoidal cells. Branches of the maxillary artery and the a. alveolaris superior posterior, palatine nerves (nn. palatini from the pterygopalatine ganglion), and rr. alveolares superiores posteriores approach the tuberosity.
- Inner (medial) wall: anteriorly borders the nasolacrimal canal, and in the posterosuperior part is adjacent to the ethmoid bone cells.
- Inferior wall: represented by the alveolar process of the maxilla.
Topography of vessels and nerves of the lateral nasal wall
The lateral wall of the nasal cavity features a complex and dense vascular and neural network that provides sensitivity, secretion, and blood supply to the surrounding tissues.
Nervous system includes several pairs of cranial nerves (CN) and autonomic ganglia:
- Pair I (olfactory nerve): represented by nn. olfactorii and the olfactory bulb (bulbus olfactorius).
- Pair II: optic nerve (n. opticus).
- Pair V (trigeminal nerve): three main branches arise from the trigeminal ganglion (ganglion trigeminale). The first is n. ophthalmicus, the second is n. maxillaris (having connections with the pterygopalatine ganglion), and the third is n. mandibularis (giving off the auriculotemporal nerve — n. auriculotemporalis, and the lingual nerve — n. lingualis).
- Pair VII (facial nerve): n. facialis, greater petrosal nerve (n. petrosus major), and chorda tympani (chorda tympani).
- Pair VIII: vestibulocochlear nerve (n. vestibulocochlearis).
- Ganglia: the pterygopalatine ganglion (ganglion pterygopalatinum) gives rise to the nerve of the pterygoid canal, palatine nerves (greater, lesser, anterior), and nasopalatine nerve. The otic ganglion (ganglion oticum) is also located in this region.
Blood supply is provided by the external and internal carotid artery systems. These include the ophthalmic artery (a. ophthalmica), maxillary artery (a. maxillaris), middle meningeal artery (a. meningea media), sphenopalatine artery (a. sphenopalatina) with its palatine branches, as well as the anterior and posterior ethmoidal arteries.
Frontal sinus (sinus frontalis)
The frontal sinus is extremely variable in size. In some cases, it may be completely absent, while in others, it extends to the zygomatic processes of the frontal bone, lesser wings, and even the optic canal of the sphenoid bone. The cavity is divided by a septum into right and left halves, and this septum often deviates from the strict sagittal plane.
The anterior wall of the frontal sinus is the strongest and thickest, forming the bony framework of the frontal region. It is through this wall that surgeons perform surgical access—trepanation. The posterior and inferior walls can be thinned, posing a risk of inflammation (frontal sinusitis) spreading into the anterior cranial fossa or the orbit.
Sphenoid sinus (sinus sphenoidalis)
This sinus is located directly within the body of the sphenoid bone and has a complex spatial topography bounded by six walls. Internally, it is divided by a septum (septum sinuum sphenoidalium), which is rarely located strictly in the center.
- The anterior wall in its medial part contains an aperture (apertura sinus sphenoidalis), through which the sinus communicates with the nasal cavity.
- The inferior wall forms the roof of the nasal cavity.
- The superior wall in its middle section corresponds to the hypophyseal fossa (sella turcica), and anterior to it lies the optic chiasm (chiasma opticum).
- The lateral wall (its upper part) lies directly adjacent to the cavernous sinus (sinus cavernosus) and the structures passing through it.
Ethmoidal labyrinth (labyrinthus ethmoidalis)
The ethmoidal labyrinth is located anterior to the body of the sphenoid bone and participates in the formation of the lateral wall of the nasal cavity. Superiorly it is bounded by the orbital part of the frontal bone, inferiorly by the body of the maxilla, and laterally by the lacrimal bone and the orbital plate of the ethmoid bone.
The system of air-filled cavities of the labyrinth is divided into cells (cellulae):
- Anterior (anteriores) and middle (mediae) cells open into the middle nasal meatus.
- Posterior (posteriores) cells drain into the superior nasal meatus.
The bony walls of the cells are very thin. The optic nerve canal runs in close proximity to the posterior cells, so in purulent processes, inflammation can rapidly spread to the optic nerve, the orbital cavity, or the cranial cavity.
Briefly: answers to topical questions
Where is the ostium of the frontal sinus located and where does it open?
The ostium of the frontal sinus (sinus frontalis) opens into the middle nasal meatus of the nasal cavity. Anatomically, it is located in the anterosuperior part of the semilunar hiatus (hiatus semilunaris), which is situated directly beneath the middle nasal concha. For comparison, the maxillary sinus opens into the posteroinferior part of this same hiatus.
What structures pass through the lateral wall of the sphenoid sinus?
Important neurovascular structures are adjacent to the lateral wall of the sphenoid sinus (sinus sphenoidalis), although direct passage of structures through the wall itself is not described in the sources. The upper part of the lateral wall is adjacent to the following structures:
- Cavernous sinus (sinus cavernosus)—and its contents (internal carotid artery, abducens nerve).
- Maxillary nerve—the second branch of the trigeminal nerve.
- Optic nerves—lie in close contact with the sinus wall.
What vessels and nerves pass through the cribriform plate of the ethmoid bone?
The olfactory nerves (nn. olfactorii / fila olfactoria)—15–20 thin filaments formed by axons of olfactory receptor cells—pass through the openings of the cribriform plate (lamina cribrosa ossis ethmoidalis). Fibers of the terminal nerve (n. terminalis) run among the olfactory nerve fibers. The cited sources do not describe the passage of blood vessels through the cribriform plate.
Class and exam questions
Which of the paranasal sinuses is the largest?
The largest is the maxillary sinus (sinus maxillaris). It has the shape of a four-sided pyramid and occupies the space from the first premolar to the maxillary tuberosity.
How does the sphenoidal sinus communicate with the nasal cavity?
On the anterior wall of the sphenoid sinus, in its medial part, there is a special opening—apertura sinus sphenoidalis, through which communication with the nasal cavity occurs.
Where do the ethmoidal labyrinth cells open?
The anterior and middle cells open into the middle nasal meatus, whereas the posterior cells drain into the superior nasal meatus.
What is the clinical hazard of ethmoidal labyrinth inflammation?
The walls of the ethmoidal cells are very thin, and the posterior cells lie adjacent to the optic nerve canal. During inflammation, the process can spread to this nerve, as well as into the orbit or cranial cavity.
What else to study on this topic
- Topography and branches of the pterygopalatine ganglion (ganglion pterygopalatinum)
- Formation and anatomy of the superior dental plexus (plexus dentalis superior)
- Relationship of the sphenoidal sinus with the cavernous sinus and structures of the sella turcica
- Surgical approaches to the paranasal sinuses: trepanation of the frontal sinus and surgery on the maxillary sinus
- Blood supply to the lateral wall of the nasal cavity: branches of the internal and external carotid arteries
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