Paranasal Sinuses

The 4 pair of paranasal sinuses include the maxillary, ethmoid, sphenoid, and frontal sinuses. The sinuses are a group of air-filled cavities located within the facial and cranial skeleton; all are connected to the main nasal cavity and nasopharynx. Functions include contributing to voice resonance, reducing the skull weight to facilitate an upright head position, conditioning (warming and humidifying) inhaled air, and maximizing the surface of the nasal mucosa.

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Maxillary Sinuses

Overview

  • The largest of the paranasal sinuses
  • Pyramid-shaped sinus
  • Drains into the middle meatus
  • Present at birth and fully pneumatized (air-filled) by the age of 7

Relations

  • Medial wall: the lateral wall of the main nasal cavity
  • Roof: the floor of the orbit
  • Anterior wall: contains the infraorbital foramen
  • Anterolateral walls: lateral maxilla
  • Floor: the alveolar process of the maxilla (close to the roots of the 4 molars)
  • Posterior wall: borders the pterygopalatine and infratemporal fossa

Neurovasculature

  • Lymphatic drainage: submandibular lymph nodes 
  • Blood supply: anterior, middle, and posterior superior alveolar arteries
  • Innervation: maxillary branches (V2) of the trigeminal nerve
Sinusitis

The maxillary sinuses (pink) are pyramid-shaped sinuses within the cheeks.

Image by Lecturio.

Frontal Sinuses

Overview

  • Large, irregularly shaped, chambered sinus (can be congenitally hypoplastic/aplastic)
  • Appears at the age of 6 and fully develops during adulthood
  • Drains via the frontonasal duct into the semilunar hiatus in the middle nasal meatus

Relations

  • Floor: orbital roof (danger of perforation into the orbital cavity in sinusitis), anterior ethmoidal sinuses, and nasal cavity
  • Superoposterior wall: base of the skull (danger of intracranial infection) 
  • Anterior wall: superciliary arches

Neurovasculature

  • Lymphatic drainage: submandibular lymph nodes
  • Blood supply: anterior ethmoidal, supraorbital, and supratrochlear arteries (branches of the internal carotid artery via the ophthalmic artery)
  • Innervation: branches of the ophthalmic nerve (V1)
Sinusitis

The frontal sinuses (blue) are irregularly shaped sinuses above the orbital cavities.

Image by Lecturio.

Ethmoid Sinuses

Overview

  • Numerous (3–18), thin-walled cavities (located in the ethmoidal labyrinth)
  • Not usually present at birth, but pneumatized by the age of 2
  • Divided into anterior and posterior groups and separated by the basal lamella:
    • The posterior group drains into the superior meatus above the middle nasal concha.
    • The anterior group drains into the middle meatus via the infundibulum.

Relations

  • Superior wall: floor of anterior cranial fossa and frontal bone
  • Lateral walls: medial wall of the orbital cavity 
  • Medial walls: superolateral walls of the nasal cavity

Neurovasculature

  • Lymphatic drainage:
    • Anterior and middle ethmoid sinuses to the submandibular lymph nodes
    • Posterior ethmoid sinus to the retropharyngeal lymph nodes
  • Blood supply:
    • Anterior and posterior ethmoidal arteries
    • Posterior lateral nasal branches
  • Innervation:
    • Anterior and posterior ethmoidal nerves
    • Posterior lateral superior and inferior nasal nerves
    • Orbital branches of the pterygopalatine ganglion
Sinusitis

The ethmoid sinuses (yellow) are thin-walled sinuses medial to the optic cavities.

Image by Lecturio.

Sphenoidal Sinuses

Overview

  • The most posterior sinus: variable shape and size
  • Rarely symmetrical
  • Drains into the sphenoethmoidal recess
  • Appears at the age of 3 and fully develops during adulthood

Relations

  • Floor: roof of the nasopharynx and pterygoid canal 
  • Anterior wall: posterior wall of the nasal cavity
  • Roof: proximity to:
    • Sella turcica
    • Pituitary gland
    • Optic chiasm
    • Front and middle cranial fossa
  • Lateral walls: proximity to:
    • Internal carotid artery
    • Optic canal
    • Cavernous sinus
  • Medial wall: septum of the sphenoid bone

Neurovasculature

  • Lymphatic drainage: retropharyngeal lymph nodes
  • Blood supply: posterior ethmoidal artery and posterior lateral nasal arteries
  • Innervation: posterior ethmoidal nerve and orbital branch of the pterygopalatine ganglion 
Sinusitis

The sphenoidal sinuses (green) are located posterior to the ethmoid sinuses (yellow).

Image by Lecturio.

Clinical Relevance

  • Sinusitis: inflammation of the mucous membrane of the paranasal sinuses. Sinusitis is extremely common and usually presents concurrently with rhinitis (inflammation of the nasal mucosa). The cause can be a viral, bacterial, or fungal infection, or an allergic reaction. Sinusitis can present as either acute or chronic inflammation and most commonly affects the maxillary sinuses. 
  • Choanal atresia: a congenital condition characterized by an obstruction of the posterior nasal aperture leading into the nasopharynx, which can manifest unilaterally or bilaterally. Bilateral choanal atresia manifests as obstructed nasal breathing with intermittent cyanosis immediately after birth.
  • Mucormycosis: an angioinvasive fungal infection. Inhalation of fungal spores can cause rhinocerebral mucormycosis or pulmonary mucormycosis. The clinical presentation results from fungal hyphae invading the blood vessels, causing thrombosis and (ultimately) tissue necrosis. Diagnosis is confirmed with the identification of the organism on histopathology from biopsy specimens. Patients must be treated aggressively with surgical resection of infected tissues and systemic antifungals. 

References

  1. Petrikkos, G., et al. (2012). Epidemiology and clinical manifestations of mucormycosis. Clin Infect Dis. 54 (Suppl 1), S23–34. https://www.doi.org/10.1093/cid/cir866
  2. Cox, G.M. (2021). Mucormycosis (zygomycosis). In Bond, S. (Ed.), UpToDate. Retrieved June 4, 2021, from https://www.uptodate.com/contents/mucormycosis-zygomycosis
  3. Isaacson, G.C. (2021). Congenital anomalies of the nose. In Messner, A. (Ed.), UpToDate. Retrieved July 2021, from https://www.uptodate.com/contents/congenital-anomalies-of-the-nose

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