Frontal and Ethmoid Sinuses

• The frontal sinus is located in the frontal bone anteriorly and the frontal lobe of the brain posteriorly.
• Frontal sinus infections can spread to the frontal lobe.
• The orbital roof is inferior to the frontal sinus and can be affected by frontal sinus issues.
• The septum divides the two frontal sinuses medially.
• Septum corrosion can occur between the sinuses.

Ethmoid Sinus

• The ethmoid bone, which houses the ethmoid sinus, is positioned between the orbits.
• The ethmoid sinus contains anterior, posterior, and middle ethmoidal air cells.
• Ethmoidal air cell configurations vary among individuals.
• Superiorly, the cribriform plate forms the floor of the anterior cranial fossa.
• Olfactory nerve rootlets pass through the cribriform plate and are vulnerable to injury.
• The medial orbital wall borders the ethmoid sinus laterally.
• Thin lateral walls of ethmoid air cells are prone to fracture from trauma.
• Fractures can cause air to enter the orbit or orbital fat to enter the ethmoid air cells.
• The nasal cavity lies medially, and the sphenoid sinus posteriorly.
• The ethmoid sinus is adjacent to the sphenoid air cells.

Sphenoid Sinus

• The sphenoid sinus offers surgical access to various structures.
• The pituitary gland and optic chiasm are superior to the sphenoid sinus.
• Pituitary tumors can affect hormone production and impinge on the optic chiasm.
• The cavernous sinus, cranial nerves (III, VI, V1, V2), and the internal carotid artery are located laterally.
• The internal carotid artery passes through the cavernous sinus.

Maxillary Sinus

• The orbital floor and infraorbital vessels and nerves are superior to the maxillary sinus.
• Thin orbital floor bones are susceptible to fracture from maxillary sinus issues.
• Molar and premolar roots are inferior to the maxillary sinus.
• Long-term sinus issues may erode bone and affect molar teeth.
• Oral abscesses, resulting from tooth infections, can drain into the maxillary sinus.
• The nasal cavity is medial to the maxillary sinus.

Sinusitis

• Sinusitis involves inflammation of the sinus mucosa.
• Mucus overproduction disrupts the normal balance, leading to accumulation and bacterial colonization.
• Mucus thickens, becomes viscid, and gets trapped, leading to chronic sinusitis.
• Bright orange mucus indicates a sinus infection.
• Treatments include antibiotics and steroids.
• Surgery, such as FESS, may be needed to correct anatomical variations hindering drainage.
• FESS involves improving nasal drainage by modifying bone or anatomical anomalies in the ethmoid bone.
• Transsphenoidal or sublabial approaches are used in surgery.

Nasal Skeleton

• Unpaired bones of the nasal skeleton include the ethmoid, sphenoid, frontal, vomer.
• Paired bones of the nasal skeleton include the nasal, maxillary, palatine, lacrimal, and conchae.
• The medial wall comprises the perpendicular plate of the ethmoid bone, septal cartilage, and vomer.
• The lateral wall features the superior, middle, and inferior conchae (turbinates).
• Turbinates (conchae) project medially from the lateral wall.
• A conchae is a bony shelf.
• A turbinate is a conchae with soft tissue covering.
• A meatus is the space beneath each shelf.
• The superior turbinate sits above the superior meatus.
• The middle turbinate sits above the middle meatus.
• The inferior turbinate sits above the inferior meatus.

Turbinates and Airflow

• Turbinates are visible on CT scans.
• Turbinates and meatuses increase the surface area of the respiratory epithelium.
• Airflow becomes turbulent, increasing heat and humidity.
• Airflow alternates between nostrils, allowing the lateral wall to recover.

Sinus Openings

• The sphenoethmoidal recess is where the sphenoidal air sinuses open, located near the superior turbinate.
• The bulla ethmoidalis/hiatus semilunaris provide openings for the anterior ethmoidal, middle ethmoidal, and maxillary air sinuses beneath the middle turbinate.
• The ostiomeatal complex is where the anterior, middle, and maxillary channels open, along with the frontal sinuses.
• Surgical targeting of the ostiomeatal complex can relieve chronic sinusitis by improving sinus drainage.
• The nasolacrimal duct carries tears and opens beneath the inferior turbinate into the inferior meatus, aiding humidification.
• CNDO (congenital nasolacrimal duct obstruction) causes excess tearing and discharge.

Innervation

• Special sensory innervation includes Olfactory CN I and Terminal CN 0.
• General somatosensory innervation includes Ophthalmic (CN V1) for the superior and anterior lateral wall and septum, and Maxillary (CN V2) for the posterior and inferior lateral wall and septum.
• The ocular sneeze reflex involves general sensory input from the nose and cornea, triggering a sneeze from sudden light changes.

Arterial Supply

• The septum's arterial supply includes the anterior ethmoidal (anterosuperior), posterior ethmoidal (posteroinferior), sphenopalatine (posteroinferior), greater palatine, and superior labial arteries.
• The lateral wall's arterial supply includes the anterior ethmoidal, posterior ethmoidal, sphenopalatine, and greater palatine arteries.

Venous Drainage

• Nasal cavity veins lack valves, allowing bidirectional flow to the brain and superficial face structures.
• Infections can spread from the nasal cavity to the CNS via these valveless veins.

Epistaxis (Nosebleed)

• In Little’s area (anterior), arterial bleeds from the anastomosis of the sphenopalatine, anterior ethmoid, and palatine arteries account for 90% of nosebleeds.
• Blood flows from one nostril when the head is tilted forward.
• These nosebleeds are more common in younger individuals and are easier to manage.
• Woodruff’s plexus (posterior) involves venous bleeding, or arterial if the sphenopalatine artery is damaged.
• Blood tends to flow backward into the nasopharynx; may gush from both nostrils.
• These nosebleeds are more common in older individuals and are more difficult to manage, often requiring treatment at the back of the nasal cavity.