Paranasal sinuses

Paranasal sinuses
Paranasal sinuses.
Lateral projection of the paranasal sinuses
Latin	sinus paranasales
Gray's	subject #223 998
MeSH	Paranasal+Sinuses
Dorlands/Elsevier	Paranasal sinuses

Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity (maxillary sinuses), above the eyes (frontal sinuses), between the eyes (ethmoid sinuses), and behind the ethmoids (sphenoid sinuses). The sinuses are named for the facial bones in which they are located.

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 antrechea 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 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.
• 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.
• Regulation of intranasal and serum gas pressures
• Immunological defense

Despite these various proposals, the paranasal sinuses may not serve any biological function at all, instead developing as spandrels during ontogeny.

Ailments

For more details on this topic, see Sinusitis.

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 that 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 decongestants, which cause 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. Men are much more often affected than women. They most often occur in the age group between 40 and 70 years. Carcinomas are more frequent than sarcomas. Metastases are rare. Tumours of the sphenoid and frontal sinuses are extremely rare.

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

• Paranasal+sinuses at eMedicine Dictionary
• The Anatomy Wiz: CT Paranasal Sinuses
• Sinus Problems FAQ
• Sinusitis: Symptoms, Causes, and Treatment
• University of Texas Medical Branch: Paranasal Sinus Anatomy and Function