Paranasal sinuses
 | This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations. (April 2009) |
| Paranasal sinuses | |
|---|---|
 Paranasal sinuses. | |
 Lateral projection of the paranasal sinuses | |
| Details | |
| Identifiers | |
| Latin | sinus paranasales |
| MeSH | D010256 |
| TA98 | A06.1.03.001 |
| TA2 | 3176 |
| FMA | 59679 |
| Anatomical terminology | |
Paranasal sinuses are air-filled spaces, communicating with the nasal cavity, within the bones of the skull and face.
Types in humans
Humans possess a number of paranasal sinuses, divided into subgroups that are named according to the bones within which the sinuses lie:
- the maxillary sinuses, also called the maxillary antra and the largest of the paranasal sinuses, are under the eyes, in the maxillary bones.
- the frontal sinuses, superior to the eyes, in the frontal bone, which forms the hard part of the forehead.
- the ethmoid sinuses, which are formed from several discrete air cells within the ethmoid bone between the nose and the eyes.
- the sphenoid sinuses, in the sphenoid bone at the center of the skull base under the pituitary gland.
The paranasal air sinuses are lined with respiratory epithelium (ciliated pseudostratified columnar epithelium).
Development
Paranasal sinuses form developmentally through excavation of bone by air-filled sacs (pneumatic diverticula) from the nasal cavity. This process begins prenatally, and it continues through the course of an organism's lifetime
Sinuses in animals
Paranasal sinuses occur in a variety of animals (including most mammals, birds, non-avian dinosaurs, and crocodilians). In non-humans, the bones occupied by sinuses are quite variable.
Biological function
The biological role of the sinuses is debated, but a number of possible functions have been proposed:
- Decreasing the relative weight of the front of the skull, and especially the bones of the face. The shape of the facial bones is important, as a point of origin and insertion for the muscles of facial expression.
- Increasing resonance of the voice.
- Providing a buffer against blows to the face.
- Insulating sensitive structures like dental roots and eyes from rapid temperature fluctuations in the nasal cavity.
- Humidifying and heating of inhaled air because of slow air turnover in this region.
Ailments
The paranasal sinuses are joined to the nasal cavity via small orifices called ostia. These become blocked easily by allergic inflammation, or by swelling in the nasal lining which occurs with a cold. If this happens, normal drainage of mucus within the sinuses is disrupted, and sinusitis may occur.
These conditions may be treated with drugs such as pseudoephedrine, which causes vasoconstriction in the sinuses, reducing inflammation, by traditional techniques of nasal irrigation, or by corticosteroid.
Malignancies of the paranasal sinuses comprise approximately 0.2% of all malignancies. About 80% of these malignancies arise in the maxillary sinus. Tumours of the sphenoid and frontal sinuses are extremely rare.
Other sinuses
The paranasal sinuses are not the only sinuses within the skull: the mastoid cells in the mastoid bone around the middle ear are also a type of sinus.
Etymology
Sinus is a Latin word meaning a fold or pocket; in particular the front pocket in a toga.
Additional images
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Paranasal sinuses
External links
