The ethmoid bone is divided into two parts: the perpendicular plate and the horizontal plate. There are usually three turbinates - superior, middle, and inferior - that are seen on endoscopy of the nose. The middle turbinate is part of the ethmoid bone and covers several structures. The uncinate process is attached to surrounding bones and covers the maxillary hiatus along with other structures. The ethmoidal infundibulum is a funnel-shaped passage bounded by various structures that tapers posteriorly. Pneumatization from ethmoidal cells can extend to surrounding areas to form additional cells.

1. Endoscopic anatomy of
ethmoid bone

2. • ethmoid bone is divided into 2 parts
• perpendicular plate of ethmoid
• horizontal plate of ethmoid

4. ethmoid bone:

5. • turbinates are the major structures seen on endoscopy of the nose.
• passage between turbinates are called meati/ meatus.
• there are usually 3 turbinates superior, middle and inferior turbinates
with their respective meatus
• inferior turbinate is a separate bone but superior and middle
turbinate are the part of ethmoid bone.

7. aggar nasi:
• most anterior part of ethmoid bone
• it is the pneumatised lacrimal bone and ethmoid crest of frontonasal
process of maxilla
• present just anterior to the attachment of middle turbinate

9. agger nasi relations
• just above and anterior to middle turbinate
• anteriorly - frontal process of maxilla
• superiorly - frontal recess/ frontal sinus
• antero laterally - nasal bone
• inferomedially - uncinate process
• inferolaterally - lacrimal bone

10. middle turbinate:
• part of ethmoid bone.
• dried leaf in shape
• covers maxillary hiatus,uncinate process, bulla ethmoidalis, hiatus
semilunaris
• has curved course with passing in three planes

11. middle turbinate:
• divides into 3 segments
• basal lamella of middle turbinate
divides ethmoid labyrinth into
anterior and posterior ethmoid
air cells

12. middle turbinate attachments
• 1st part - frontonasal process of maxilla and cribriform plate
• 2nd part - lamina papyracea
• 3rd part - perpendicular plate of palatine bone

14. • swollen middle turbinate is called as concha bullosa

15. uncinate process
• seen after reflecting the middle
turbinate
• attached to
• lacrimal bone and frontonasal
process of maxilla anteriorly
• inferior turbinate inferiorly
• posteriorly, it is free but related to
the perperndicular plate of
palatine bone

16. • based on its superior attachment, anatomical variations of uncinate
process are noted

17. • uncinate process is one of the 4 structures that cover the maxillary
hiatus
• the other 3 include
• lacrimal bone
• inferior turbinate
• palatine bone (maxillary process)

18. bulla ethmoidalis:
• most constant anterior ethmoidal air cell
• largest ant. ethmoid cell
• attached to basal lamella of middle turbinate
• present posterior to the uncinate process
• superiorly, wall of bulla extend to skull base

21. hiatus semilunaris:
• sickle shaped 2 dimensional cleft
• between posterior free margin of uncinate process and anterior wall
of bulla ethmoidalis
• forms the doorway to ethmoidal infunibulum
• usually, it is referred to as hiatus semilunaris inferioris whereas,
opening of lateral sinus of grunwald is referred to as hiatus
semilunaris inferioris.( between bulla and middle turbinate)

23. sinus lateralis
• seen if the posterior wall of bulla is not in contact with basal
lamella of middle turbinate
• the recess above bulla between bulla and skull base is called
suprabullar recess
• the recess behind bulla between bulla and basal lamella is
called as retrobullar recess
• together forms sinus lateralis
• boundaries are
• posteriorly - basal lamella
• anteriorly - bulla
• superiorly - skull base
• laterally - lamina papyraceae

25. ethmoidal infundibulum:
• cleft like 3 dimensional space in lateral wall of nose
• funnel shaped passage
• boundaries are
• anteriorly - lacrimal bone
• posteriorly - bulla
• superiorly - frontal recess
• medially - uncinate process
• laterally - lamina papyraceae

26. • if uncinate process is attached to lamina papyracea, blind pouch is
seen superiorly in ethmoid infundibulum - called as RECESS
TERMINALIS. described by stammberger as an inverted egg cup.
• posteriorly, infundibulum tapers parallel to the tapering of uncinate
process

29. superior turbinate:
• 1/2 the length of middle turbinate
• starts from middle part of middle turbinate
• has opening of posterior ethmoidal cells in its meatus

30. anterior ethmoidal artery:
• canal for AEA is over superiomedial aspect of orbit - pyramidal sign

31. • anterior ethmoidal artery is a branch of ophthalmic artery given in
orbit.
• enters the nose, transverses across the roof of ethmoidal sinus in an
anteromedial direction and then leaves the nose at lateral lamella of
cribriform plate to enter in to cranial cavity
• thus the canal in which it transverses is called as orbitocranial canal.
• lateral end of canal is - suture line of frontal bone and lamina
papyracea
• medial end is - cribriform plate
• canal is 17mm below the roof of ethmoid, 1-2 mm behind the point
where anterior wall of bulla meets skull base

32. • from cranial cavity, artery turns anteriorly along the cribriform plate
in a sulcus called ethmoidal sulcus (length of ethmoid sulcus - 3 to
16mm)
• then, enters the nasal cavity on either side of crista galli

33. posterior ethmoidal artery:
• branch of ophthalmic artery.
• passes through fissure between frontal bone and lamina papyracea to
enter nasal cavity
• as it lies high in roof of ethmoid, usually not seen easily
• enters cranial cavity through cribriform plate and then again passes
through foramen in cribriform plate to enter back into nasal cavity

35. • anterior nasal crest to anterior ethmoid artery - 22 to 24 mm
• anterior to posterior ethmoidal artery - 12 to 15 mm
• posterior ethmoidal artery to optic canal - 3 to 7 mm( 6mm)

36. keros classification:
• the depth of olfactory fossa is classified by keros classification
• it is the height of lateral lamella of cribriform plate
• based on the height, it is of 3 types
• type 1 - 1 to 3 mm
• type 2 - 4 to 7 mm
• type 3 - 8 to 17 mm

38. ethmoidal cells:
• anterior ethmoidal cells are cuboidal to round in shape
• as we go posteriorly, posterior ethmoid cells are conical in shape.
• pneumatisation from ethmoidal cells can extend to the surroundings
to form
• haller cell
• supra orbital cell
• onodi cell
• frontal sinus
• agger nasi cell

39. haller cell:
• inferomedial aspect of orbital rim
• also called as orbitoethmoidal cell

40. onodi cell
• pneumatisation extending between sphenoid sinus and optic nerve

41. supra orbital cell:
• the supraorbital cell extends up into the frontal sinus posterior to
frontal recess
• can extend over the skull base

42. •