Processus uncinatus ossis ethmoidalis

The uncinate process of the ethmoid bone is a thin hook-like osseous structure of the wall of the lateral nasal cavity.

Gross anatomy

Together with the ethmoid bulla, it forms the boundaries of the hiatus semilunaris and ethmoid infundibulum.

The course of the free edge of the uncinate process is variable. Its tip is usually attached to the lateral nasal wall (most common) or to the lateral surface of the middle turbinate. It can also attach more laterally to the lamina papyracea, agger nasi cell or ethmoid roof. Attachment of its tip is important as it dictates the drainage pathway of the frontal recess:

  • when attached to the nasal wall or middle turbinate, it makes up the medial wall of the frontal recess, redirecting drainage to the ethmoid infundibulum prior to the passage into the middle meatus;
  • when attached more laterally, the uncinate process makes up the lateral wall of the frontal recess, redirecting drainage directly to the middle meatus, bypassing the ethmoid infundibulum which then forms a blind-ending recess known as the recessus terminalis.

Practical points

  • the uncinate process is usually removed during functional endoscopic sinus surgery (FESS) – uncinectomy
  • a retained uncinate process is a common cause of failed frontal FESS
  • it is important to report attachment of its tip as forceful traction during surgery may damage the ethmoid roof
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