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The ethmoid air cells consist of numerous thin-walled cavities in the ethmoidal labyrinth [4] that represent invaginations of the mucous membrane of the nasal wall into the ethmoid bone. [3] They are situated between the superior parts of the nasal cavities and the orbits, and are separated from these cavities by thin bony lamellae. [4]
The ethmoidal labyrinth or lateral mass of the ethmoid bone consists of a number of thin-walled cellular cavities, the ethmoid air cells, arranged in three groups, anterior, middle, and posterior, and interposed between two vertical plates of bone; the lateral plate forms part of the orbit, the medial plate forms part of the nasal cavity.
The ethmoid bulla (or ethmoidal bulla) is a rounded elevation upon the lateral wall of the middle nasal meatus [1] [2]: 377 (nasal cavity inferior to the middle nasal concha) produced by one or more of the underlying middle ethmoidal air cells (which open into the nasal cavity upon or superior to the ethmoidal bulla [2]: 374 [3]).
The frontonasal duct may or may not drain into the ethmoidal infundibulum - this is determined by the place of attachment of the uncinate process of the ethmoid bone: if the uncinate process is attached to the lateral nasal wall, the frontonasal duct will open directly into the middle nasal meatus; if otherwise, it will drain into the infundibulum.
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It is also called the nasoturbinal concha and the nasal ridge. In 90% of patients an anterior ethmoidal cell (called the "agger nasi cell") can be found in the lacrimal bone below the agger nasi ridge. [1] An enlarged agger nasi cell may encroach the frontal recess area, constricting it and causing mechanical obstruction to frontal sinus drainage.
The margins of the notch present several half-cells which, when united with corresponding half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells. Two grooves cross these edges transversely; they are converted into the anterior and posterior ethmoidal canals by the ethmoid, and open on the medial wall of the orbit.
the medial or ethmoidal, directed forward, articulates with the labyrinth of the ethmoid. In some cases the air cell opens on this surface of the bone and then communicates with the posterior ethmoidal cells. More rarely it opens on both surfaces, and then communicates with the posterior ethmoidal cells and the sphenoidal sinus.