Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal
cavity, above the eyes, between the eyes, and behind the ethmoids.
The sinuses are named for the facial bones in which they are located.
Structure Humans possess four paired 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 ethmoidal sinuses, which are formed from several discrete air cells within the ethmoid
bone between the nose and the eyes.
the sphenoidal sinuses, in the sphenoid bone.
The paranasal air sinuses are lined with respiratory epithelium.
Development Paranasal sinuses form developmentally through
excavation of bone by air-filled sacs from the nasal cavity.
This process begins prenatally, and it continues through the course of an organism's lifetime.
The results of experimental studies suggest that the natural ventilation rate of a sinus
with a single ostium is extremely slow.
Indeed, such limited ventilation may be protective for the sinus, as it would help prevent drying
of its mucosal surface and maintain a near-sterile environment with high NO concentrations and
minimal pathogen access.
Thus composition of gas content in the maxillary sinus is similar to venous blood, with high
CO2 and lower O2 level compared to breathing air.
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.
Clinical relevance Inflammation
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.
Because the maxillary posterior teeth are close to the maxillary sinus, this can also
cause clinical problems if any disease processes are present, such as an infection in any of
these teeth.
These clinical problems can include secondary sinusitis, the inflammation of the sinuses
from another source such as an infection of the adjacent teeth.
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.
Cancer 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.
History Etymology
Sinus is a latin word meaning a fold or pocket; in particular the front pocket in a toga.
Other animals Paranasal sinuses occur in many other animals,
including most mammals, birds, non-avian dinosaurs, and crocodilians.
The bones occupied by sinuses are quite variable in these other species.
Additional images
See also This article uses anatomical terminology;
for an overview, see anatomical terminology.
References
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