Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity.
Structure
Humans possess four pairs of paranasal sinuses, divided into subgroups that are named according to the
within which the sinuses lie. They are all innervated by branches of the
trigeminal nerve (CN V).
The paranasal sinuses are lined with respiratory epithelium (ciliated pseudostratified columnar epithelium).
Functions
One known function of the paranasal sinuses is the production of
nitric oxide, which also functions as a facilitator of oxygen uptake.
Development
Paranasal sinuses form developmentally through excavation of bone by air-filled sacs (pneumatic diverticula) from the
nasal cavity. This process begins prenatally (intrauterine life), 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 sinus ostium (opening) is extremely slow. 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 carbon dioxide concentrations and minimal pathogen access. Thus composition of gas content in the maxillary sinus is similar to venous blood, with high carbon dioxide and lower oxygen levels compared to breathing air.
At birth, only the maxillary sinus and the ethmoid sinus are developed but not yet pneumatized; only by the age of seven are they fully aerated. The sphenoid sinus appears at the age of three, and the first appear at the age of six, and fully develop during adulthood.
===CT scans, radiographs (x-ray) and other illustrations===
Clinical significance
Inflammation
The paranasal sinuses are joined to the
nasal cavity via small orifices called
Sinus ostium. These become blocked easily by allergic inflammation, or by swelling in the nasal lining that occurs with a
common 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.
[Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, p. 68]
These conditions may be treated with drugs such as , 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.
are more frequent than
. Metastases are rare.
Neoplasm of the sphenoid and frontal sinuses are extremely rare.
Etymology
Sinus is a
Latin word meaning a fold, curve, or bay. Compare
sine.
Other animals
Paranasal sinuses occur in many other animals, including most
,
, and
. They have also been discovered in non-avian
. The bones occupied by sinuses vary with species.
==Illustrations==
See also
External links
