[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) › Ethmoid bone [Skeletal system](https://durgical.com/en/anatomy/system/skeletal-system/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) # Ethmoid bone The ethmoid is a light, honeycombed bone between the eyes; it forms part of the nose and eye sockets, and its sieve-like roof lets the smell nerves through. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=head_neck&select=ethmoid_bone&side=r) Opens in the Durgical app, no sign-up needed. ## What it is A light, honeycombed bone between the eyes, forming part of the nose and the eye sockets. ## What it does Its sieve-like roof lets the smell nerves through; its air cells lighten the skull. ## Key points - The cribriform plate is the thinnest part of the anterior cranial fossa floor; a fracture here can tear the olfactory filaments and the dura, causing anosmia and CSF rhinorrhoea - Its orbital plate (lamina papyracea) is a paper-thin medial orbital wall: the route by which ethmoid sinusitis reaches the orbit and a common site of medial wall fractures - It carries the superior and middle conchae; the middle meatus under the middle concha receives the frontal, maxillary and anterior ethmoid drainage (ostiomeatal complex) ## Key facts **Joints with** Frontal, sphenoid, nasals, [maxillae](https://durgical.com/en/anatomy/maxilla/), lacrimals, palatines, vomer, inferior conchae **Landmarks** Cribriform plate, crista galli, perpendicular plate, ethmoid air cells, superior and middle conchae, orbital plate ## Relations **Above** Anterior cranial fossa: the olfactory bulbs rest on the [cribriform plate](https://durgical.com/en/anatomy/cribriform-plate/) on each side of the crista galli, which anchors the [falx cerebri](https://durgical.com/en/anatomy/falx-cerebri/); the frontal lobes lie above **Lateral** The orbits, separated from the [ethmoid cells](https://durgical.com/en/anatomy/anterior-cells-of-ethmoid-bone/) only by the lamina papyracea; the [medial rectus](https://durgical.com/en/anatomy/medial-rectus-muscle/) lies against this wall **Below** The [nasal cavity](https://durgical.com/en/anatomy/nasal-cavity/): the perpendicular plate meets the [vomer](https://durgical.com/en/anatomy/vomer/) and septal cartilage in the [nasal septum](https://durgical.com/en/anatomy/nasal-septum/), and the conchae hang from the lateral walls **In front** [Frontal bone](https://durgical.com/en/anatomy/frontal-bone/) and [nasal bones](https://durgical.com/en/anatomy/nasal-bone/); the [frontal sinus](https://durgical.com/en/anatomy/sinus-of-frontal-bone/) drains down through the frontal recess between its anterior cells **Behind** Body of the [sphenoid bone](https://durgical.com/en/anatomy/sphenoid-bone/) and the [sphenoid sinus](https://durgical.com/en/anatomy/sinus-of-sphenoid-bone/) ## How to find it It cannot be felt. On coronal CT it sits in the midline between the orbits: cribriform plate and crista galli on top, the air cells on each side and the perpendicular plate below. In endoscopic sinus surgery it is entered through the middle meatus. ## On imaging Coronal CT of the paranasal sinuses (bone window) shows the height and slope of the cribriform plate, the lamina papyracea and the ethmoid cells; it is the standard map before endoscopic sinus surgery. ## Clinical notes - Clear, watery nasal drip after head trauma suggests CSF rhinorrhoea through a cribriform plate fracture, with a risk of meningitis; beta-2 transferrin in the fluid confirms CSF - Loss of smell after a blow to the head can follow shearing of the [olfactory nerve](https://durgical.com/en/anatomy/olfactory-nerve/) filaments where they pass through the cribriform plate - In endoscopic sinus surgery the lamina papyracea (orbit) and the skull base above (CSF leak) are the two walls not to breach - A blind nasal tube is avoided when an anterior skull base fracture is suspected, because it can pass through a broken cribriform plate into the cranial cavity ## Anatomical variants - Concha bullosa: an air cell inside the middle concha; common and usually harmless, though a large one can narrow the middle meatus - Infraorbital ethmoid (Haller) cells: cells that extend along the orbital floor and can crowd the outflow of the [maxillary sinus](https://durgical.com/en/anatomy/maxillary-sinus/) - Sphenoethmoidal (Onodi) cell: a posterior ethmoid cell reaching beside or above the sphenoid sinus, next to the [optic nerve](https://durgical.com/en/anatomy/optic-nerve/) - Agger nasi cell: the most anterior ethmoid cell, in front of the attachment of the middle concha; its size shapes the frontal recess ## Development Ossifies in cartilage from three centres: one in each labyrinth before birth and one for the perpendicular plate and crista galli after birth; they fuse in early childhood. The ethmoid cells already exist at birth, so ethmoid sinusitis can occur in infants. (Some texts describe two medial centres, four in all; ossification is complete by about 5–6 years.) ## Test yourself Think of the answer, then tap the question to see it. ## What can a fracture of the cribriform plate of the ethmoid bone cause? Anosmia from torn olfactory filaments and CSF rhinorrhoea from a dural tear, with a risk of meningitis. ## Why does ethmoid sinusitis spread to the orbit? The orbital plate of the ethmoid bone (lamina papyracea) is a paper-thin medial orbital wall separating the ethmoid cells from the orbit. ## Which conchae belong to the ethmoid bone, and what drains into the middle meatus? The superior and middle conchae; the middle meatus receives frontal, maxillary and anterior ethmoid drainage (ostiomeatal complex). ## Which test on clear nasal fluid after head trauma confirms CSF from a cribriform plate fracture? Beta-2 transferrin in the fluid confirms that it is CSF. ## Why is a blind nasal tube avoided when an anterior skull base fracture is suspected? It can pass through a broken cribriform plate of the ethmoid bone into the cranial cavity. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/anatomy/ethmoid-bone/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** os ethmoideum TA2 721 **Official Spanish (DeCS)** Hueso Etmoides DeCS D005004 **English (TA2)** Ethmoid bone **Also called** ethmoid · ethmoidal bone · os ethmoides Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=5096&filter=ths_termall&q=Ethmoid%20Bone); [Anatomy, Head and Neck, Ethmoid Bone](https://www.ncbi.nlm.nih.gov/books/NBK544328/); [Anatomy, Head and Neck, Skull](https://www.ncbi.nlm.nih.gov/books/NBK499834/); Anatomía humana (4.ª ed.), tomo 1, cap. 9: Huesos del neurocráneo. ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/ethmoid-bone/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/ethmoid-bone/