Nose and Paranasal Sinuses
The bones forming the medial, inferior, and superior orbital walls are close to the nasal cavity and are pneumatized by the paranasal sinuses, which arise from and drain into the nasal cavity. The sinuses decrease the weight of the skull and function as resonators for the voice. The sinuses also support the nasal passages by trapping irritants and by warming and humidifying inhaled air. Pathophysiologic processes in these spaces that secondarily affect the orbit include sinonasal carcinomas, inverted papillomas, zygomycoses, granulomatosis with polyangiitis (formerly, Wegener granulomatosis), and mucoceles, as well as sinusitis, which may cause orbital cellulitis or abscess.
The nasal cavity is divided into 2 nasal fossae by the nasal septum. The lateral wall of the nose has 3 bony projections: the superior, middle, and inferior conchae (turbinates). The turbinates are covered by nasal mucosa, and they overhang the corresponding meati. Just cephalad to the superior concha is the sphenoethmoidal recess, into which the sphenoid sinus drains. The frontal sinus, the maxillary sinus, and the anterior and middle ethmoid air cells drain into the middle meatus. The nasolacrimal duct opens into the inferior meatus. The nasal cavity is lined by a pseudostratified, ciliated columnar epithelium with copious goblet cells. The mucous membrane overlying the lateral alar cartilage is hairbearing and, therefore, less suitable for use as a composite graft in eyelid reconstruction than the mucoperichondrium over the nasal septum.
The frontal sinuses develop from evaginations of the frontal recess and cannot be seen radiographically until the sixth year of life. Pneumatization of the frontal bone continues through childhood and is complete by early adulthood (Fig 1-11). The sinuses can develop asymmetrically and vary greatly in size and shape. Each frontal sinus drains through a separate frontonasal duct and empties into the anterior portion of the middle meatus.
The ethmoid air cells are thin-walled cavities that lie between the medial orbital wall and the lateral wall of the nose. They are present at birth and expand as the child grows. Ethmoid air cells can extend into the frontal, lacrimal, and maxillary bones and may extend into the orbital roof (supraorbital ethmoids). The numerous small, thin-walled air cells of the ethmoid sinus are divided into anterior, middle, and posterior. The anterior and middle air cells drain into the middle meatus; the posterior air cells, into the superior meatus. Sinusitis in the ethmoids is a common cause of orbital cellulitis and medial orbital subperiosteal abscess when the inflammation or infection spreads into the orbit.
Figure 1-11 Relationship of the orbits to the paranasal sinuses. FS, frontal sinus; ES, ethmoid sinus; MS, maxillary sinus; SS, sphenoid sinus.
The sphenoid sinus evaginates from the posterior nasal roof to pneumatize the sphenoid bone. It is rudimentary at birth and reaches full size after puberty. The sinus drains into the sphenoethmoidal recess of each nasal fossa. The optic canal is located immediately superolateral to the sinus wall. Pathologic processes involving the sphenoid sinus compress the optic nerve, leading to visual field abnormalities and vision loss.
The maxillary sinuses are the largest of the paranasal sinuses. The roof of the maxillary sinus forms the floor of the orbit. The maxillary sinuses extend posteriorly in the maxillary bone to the inferior orbital fissure. The infraorbital nerve and artery travel along the roof of the sinus from posterior to anterior. The bony nasolacrimal canal lies within the medial wall. The sinus drains into the middle meatus of the nose by way of the maxillary ostium. Orbital blowout fractures commonly disrupt the floor of the orbit medial to the infraorbital canal, where the bone is thinnest. The infraorbital nerve is often compromised, causing hypoesthesia of the cheek, upper lip, and maxillary teeth.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.