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A sinus is a sac or cavity in any organ or tissue, or an abnormal cavity or passage. In common usage, "sinus" usually refers to the paranasal sinuses, which are air cavities in the cranial bones, especially those near the nose and connecting to it. Most individuals have four paired cavities located in the cranial bone or skull.
The frontal sinuses are located in the frontal bone; the sphenoidal sinuses in the sphenoid bone; the maxillary sinuses in the maxilla; and the ethmoidal sinuses in the ethmoid bone. [2] [13] A narrow opening called a sinus ostium from each of the paranasal sinuses allows drainage into the nasal cavity. The maxillary sinus is the largest of the ...
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 ...
Frontal sinuses are rarely symmetrical as the septum between them frequently deviates to either side of the midline. [3] [1] The two sinuses also vary in extent compared to one another. [2] Their size of the frontal sinuses is highly variable. [2] Rarely, one or both sinuses is hypoplastic [1] or even absent. [1] [2]
The pyramid-shaped maxillary sinus (or antrum of Highmore) is the largest of the paranasal sinuses, located in the maxilla. It drains into the middle meatus of the nose [1] [2] through the semilunar hiatus. It is located to the side of the nasal cavity, and below the orbit. [2]
The sphenoid sinus is a paired paranasal sinus in the body of the sphenoid bone. It is one pair of the four paired paranasal sinuses. [1] The two sphenoid sinuses are separated from each other by a septum. Each sphenoid sinus communicates with the nasal cavity via the opening of sphenoidal sinus.
The paranasal sinuses are connected to the nasal cavity through small orifices called ostia. Most of these ostia communicate with the nose through the lateral nasal wall, via a semi-lunar depression in it known as the semilunar hiatus. The hiatus is bound laterally by a projection known as the uncinate process.
The ethmoid sinuses or ethmoid air cells of the ethmoid bone are one of the four paired paranasal sinuses. [1] Unlike the other three pairs of paranasal sinuses which consist of one or two large cavities, the ethmoidal sinuses entail a number of small air-filled cavities ("air cells"). [ 2 ]