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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 four pairs of paranasal sinuses – the maxillary, ethmoid, sphenoid, and frontal, develop from the nasal cavity as invaginations extending into their named bones. Two pairs of sinuses form during prenatal development and two pairs form after birth. The maxillary sinuses are the first to appear during the fetal third month.
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 ...
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. [2]: 500 The two sphenoid sinuses vary in size ...
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 ]
The frontal sinuses are one of the four pairs of paranasal sinuses that are situated behind the brow ridges. Sinuses are mucosa -lined airspaces within the bones of the face and skull. Each opens into the anterior part of the corresponding middle nasal meatus of the nose through the frontonasal duct which traverses the anterior part of the ...
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Sinus (anatomy), a sac or cavity in any organ or tissue Paranasal sinuses, air cavities in the cranial bones, especially those near the nose, including: Maxillary sinus, is the largest of the paranasal sinuses, under the eyes, in the maxillary bones; Frontal sinus, superior to the eyes, in the frontal bone, which forms the hard part of the forehead