Overview and topographic anatomy
General information
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The paranasal sinuses are invaginations from the nasal cavity that drain into spaces associated with the lateral nasal wall
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There are 4 paranasal sinuses:
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Frontal
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Maxillary
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Ethmoid
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Sphenoid
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Each paranasal sinus is named after the bone in which it is located
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Each is lined by a respiratory epithelium (pseudostratified columnar epithelium with cilia)
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Morphology of the sinuses is highly variable
| FEATURES OF THE PARANASAL SINUSES | ||||
|---|---|---|---|---|
| Sinus | Location | Comment | Artery | Nerve |
| Frontal | Within frontal bone |
|
Ophthalmic branches | Ophthalmic division of the trigeminal n. |
| Maxillary | Within maxillary bone |
|
Maxillary branches | Maxillary division of the trigeminal n. |
| Ethmoid | Within ethmoid bone |
|
Ophthalmic and maxillary branches | Ophthalmic and maxillary divisions of the trigeminal n. |
| Sphenoid | Within sphenoid bone |
|
||
Drainage of the paranasal sinuses and associated structures
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All paranasal sinuses drain into the nasal cavity
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Different sinuses serve as drainage conduits for different regions
| SUMMARY OF PARANASAL SINUS DRAINAGE | ||
|---|---|---|
| Region Drained | Location | Structure(s) Drained |
| Sphenoethmoidal recess | Superior to the superior concha | Sphenoid sinus |
| Superior meatus | Inferior to the superior concha | Posterior ethmoid sinus |
| Middle meatus | Inferior to the middle concha |
|
| Inferior meatus | Inferior to the inferior concha | Nasolacrimal duct |
Frontal sinus
General information
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The 2 frontal sinuses typically are asymmetric
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Usually not present at birth, or there is a small outpouching
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The most common of the paranasal sinuses to undergo aplasia
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Is the last paranasal sinus to begin to pneumatize—beginning around the 2nd year
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Usually well developed by the age of 7 or 8 years
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A prime expansion in size occurs when the 1st deciduous molars erupt and another when the permanent molars begin to appear at about age 6
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The adult frontal sinus has 2 extensions:
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Frontal—which extends superiorly into the frontal bone in the region of the forehead
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Orbital—which extends posteriorly into the frontal bone over the medial part of the orbit
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Drainage varies; may drain in front of, above, or into the ethmoidal infundibulum
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Primary lymphatic drainage is to the submandibular lymph nodes
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The frontal sinus receives its nerve supply from branches of the ophthalmic division of the trigeminal nerve
Relations of sinus
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Superior— anterior cranial fossa and contents
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Inferior— orbit, anterior ethmoidal sinuses, nasal cavity
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Anterior— forehead, superciliary arches
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Posterior— anterior cranial fossa and contents
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Medial— other frontal sinus
Location of ostium
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Middle meatus
Arterial supply
| Artery | Source | Course |
|---|---|---|
| Anterior ethmoid | Ophthalmic a. (from the internal carotid a.) |
|
| Supraorbital |
|
Nerve supply
| Nerve | Source | Course |
|---|---|---|
| Supraorbital | Ophthalmic division of the trigeminal n. |
|
Imaging
Ethmoid sinus
General information
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Ethmoid sinuses form within the ethmoid as many individual air cells
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Anatomically they are located between the superior portion of the nasal cavity and the orbit, and the surrounding bone is very thin
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From 3 to 18 total ethmoid air cells may be present on each side
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Divided into anterior, middle, and posterior groups or anterior and posterior groups (controversy exists on nomenclature, depends on your reference source)
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The most anterior ethmoidal air cells are called the agger nasi
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The middle ethmoidal air cells produce the ethmoidal bulla, a swelling that protrudes from the lateral wall of the nasal cavity and represents the largest group of ethmoidal air cells
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The most posterior group of ethmoidal air cells is closely related to the orbit
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Ethmoid air cells may invade any of the other 3 sinuses
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Primary lymphatic drainage is to the submandibular lymph nodes for the anterior and middle ethmoid sinuses, and the retropharyngeal lymph nodes for the posterior ethmoid sinus
Relations of sinus
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Superior— anterior cranial fossa and contents, frontal bone with sinus
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Medial— nasal cavity
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Lateral— orbit
Location of ostium
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Anterior— middle meatus (frontonasal duct or ethmoidal infundibulum)
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Middle— middle meatus (on or above ethmoid bulla)
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Posterior— superior meatus
