In the

ethmoid bone The ethmoid bone (; from grc, ἡθμός, hēthmós, sieve) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a ...

, a sickle shaped projection, the uncinate process, projects posteroinferiorly from the

ethmoid labyrinth 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 ...

. Between the posterior edge of this process and the anterior surface of the

ethmoid bulla The ethmoid bulla (or ethmoidal bulla) is an elevation on the lateral wall of the middle meatus of the nose. It is produced by middle ethmoidal cells. It develops during the first trimester of gestation, and varies significantly based on the size ...

, there is a two-dimensional space, resembling a crescent shape. This space continues laterally as a three-dimensional slit-like space - the

ethmoidal infundibulum The hiatus semilunaris is bounded inferiorly by the sharp concave margin of the uncinate process of the ethmoid bone In the ethmoid bone, a sickle shaped projection, the uncinate process, projects posteroinferiorly from the ethmoid labyrinth. B ...

. This is bounded by the uncinate process, medially, the

orbital lamina of ethmoid bone The orbital lamina of ethmoid bone, (or lamina papyracea or orbital lamina) is a smooth, oblong bone plate which forms the lateral surface of the labyrinth of the ethmoid bone in the skull. The plate covers in the middle and posterior ethmoidal c ...

(lamina papyracea), laterally, and the ethmoidal bulla, posterosuperiorly. This concept is easier to understand if one imagine the infundibulum as a prism so that its medial face is the hiatus semilunaris. The "lateral face" of this infundibulum contains the ostium of the maxillary sinus, which, therefore, opens into the infundibulum.

Variations

The uncinate process can be attached to either the lateral nasal wall, on the lamina papyracea (50%), the anterior cranial fossa, on the ethmoidal roof (25%), or the middle concha (25%). The superior attachment of the uncinate process determines the drainage pattern of the frontal sinus. In the first case, the infundibulum and the frontal recess are separated from each other, forcing the frontal sinus to drain directly into the middle meatus and not into the ethmoidal infundibulum. With the other configurations, the sinus will drain, firstly, into the infundibulum.

References

G., Arun et alli (2017) - Anatomical variations in superior attachment of uncinate process and localization of frontal sinus outflow tract. International Journal of Otorhinolaryngology and Head and Neck Surgery, 3(2):176-179 P.S., Hechl et alli (1997) - The hiatus semilunaris and infundibulum. Endoscopic Anatomy of the Paranasal Sinuses. Springer, Vienna

External links

* - "The bones of the

lateral nasal wall Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral con ...

." Bones of the head and neck {{musculoskeletal-stub