The Anatomy of the Ethmoid Bone

Table of Contents
View All
Table of Contents

The ethmoid bone is a cube-shaped bone located in the center of the skull between the eyes. It helps form the walls of the eye socket, or orbital cavity, as well as the roof, sides, and interior of the nasal cavity.

Very light and sponge-like in texture, the ethmoid bone is one of the most complex bones of the face.

Anatomy

The ethmoid bone has four main parts. The ethmoidal labyrinths consist of two hollow blocks of bone. The ethmoidal labyrinths are made up of multiple thin-walled compartments known as ethmoidal (air) cells. As you get older, the number of cells grows.

At birth, you will only have around three to four ethmoidal cells; however, as an adult, you will normally have around 10 to 15.

These ethmoidal cells form what is more commonly referred to as the ethmoid sinuses. The ethmoid sinus cavities are one of four pairs of sinus cavities in your face, the others being the maxillary, frontal, and sphenoid sinus cavities.

The outside edges of the ethmoidal labyrinths are referred to as the lamina papyracea or orbital lamina. The lamina papyracea makes up the majority of the inside wall of your orbital cavity and connects with the frontal bone, palatine bone, lacrimal bone, and the sphenoid bone.

In the center of the ethmoid bone, between the ethmoidal labyrinth, is the perpendicular plate, which forms the upper part of the bony nasal septum; the lower part of your nasal septum is formed by the vomer bone and the palatine bone.

The inside edges of the ethmoidal labyrinths are joined by the cribriform plate, which is also connected to the perpendicular plate. The cribriform plate is important as it forms part of the base of the skull.

Above these structures, you also have the crista galli, which attaches to part of the connective tissue that surrounds your brain, anchoring it into place.

Branching off the inside edge of the ethmoidal labyrinth, you will also find the superior and middle nasal conchae, also known as turbinates. The conchae help to increase the surface area of your nasal passages, which aids in warming, humidifying, and purifying the air breathed.

X-ray

Getty Images

Function

Because the ethmoid bone is in the middle of the face, it functions to support a variety of everyday activities. The cribriform plate has sieve-like holes that allow the olfactory nerves to locate in your nose so that you can smell things and also plays a role in your ability to taste.

Sinus cavities in the ethmoidal labyrinth help serve many important functions, including:

  • Mucus production to trap allergens or other particles that may be harmful as you breathe in through your nose
  • Vocal tone
  • Reducing the weight of the head

The nasal conchae that the ethmoid forms allow air to circulate and become humidified as it travels from your nose on the way into your lungs. The mucus that is produced in the sinus cavities lines this part of your nose, which also serves as a defense mechanism by trapping any particles that may cause illness or other reactions.

Arteries that flow to your nose also travel through several of the channels that exist in the ethmoid bone, which serves to protect these arteries from trauma.

Associated Conditions

Due to its central location in the face, the ethmoid bone is prone to fracture. However, because there are other bones around it, the ethmoid bone is rarely fractured by itself.

If fractured, it is typically part of a complex NOE (nasoorbitoethmoid) fracture. This type of fracture is usually from blunt-force trauma as you might have in an automotive accident or contact-sports injury.

Because the nasal, orbital, and ethmoid bones are highly vascularized, meaning that there are a lot of blood vessels in this area, severe nosebleeds (epistaxis) usually occurs with an NOE fracture.

Other symptoms associated with an NOE fracture include:

  • Epiphora (overflow of tears)
  • Diplopia (seeing double)
  • Enophthalmos (displacement of the eyeball
  • Telecanthus (increased distance between the inner corners of the eyes)
  • "Raccoon eyes" (bruising around the entire eye)

When visiting a doctor to be evaluated for sinusitis, you may never be told which sinus(es) are inflamed or infected. However, the type of symptoms you experience may be an indicator of which sinus cavity is causing you discomfort.

In ethmoid sinusitis, common symptoms include pain behind and between the eyes and along the sides of the nose, swelling of the eyelids, and loss of smell (olfactory dysfunction).

A deviated septum may involve part of the perpendicular plate. Depending on the severity of your case, you may not notice any symptoms. However, more severe cases may cause nosebleeds and difficulty breathing through one nostril.

Ethmoid cancer is very rare and is typically categorized as a paranasal malignancy. Prevalence is low in comparison to the more common paranasal malignancies in the maxillary or nasal sinuses.

As in all cancers, early detection improves rates of survival. If ethmoid cancer remains localized, 82 out of 100 people are still alive beyond five years. However, if ethmoid cancer has metastasized, or spread to other parts of the body, only 43 to 52 out of 100 people will surpass five years of survival.

Treatment

If you suffer trauma to the face and have symptoms of NOE fracture, you should seek medical attention immediately. Rapid diagnosis of NOE fracture with a thorough exam to determine if surgery is required is important to optimal recovery.

Most sinusitis is caused by a virus, so antibiotics will generally not be recommended. If you are immunocompromised, your risk will be higher for having either a bacterial or a fungal sinus infection.

However, under the following criteria, your doctor may start you on an antibiotic—likely amoxicillin/clavulanate—even without a positive culture:

  1. You have mild to moderate symptoms lasting 10 days or more.
  2. You have severe symptoms such as elevated temperature or severe pain for greater than or equal to three days.
  3. You have worsening symptoms after having started to get better (referred to as "double sickening").

If your doctor is concerned that polyps are the underlying cause of your symptoms, a computed tomography (CT) scan will likely be ordered.

Your doctor may also use a fiber optic scope to visualize inside your nose and sinus cavities. Treatment of polyps in the ethmoid sinuses or correction of deviated septums can be performed surgically.

Proper diagnosis and treatment of an ethmoid bone/sinus cancer or other paranasal cancers will involve multiple care providers. Members of your interdisciplinary team may include:

  • Otolaryngologist (ear, nose, and throat doctor)
  • Neurosurgeon
  • Radiation oncologist
  • Medical oncologist

If the tumor is small and/or noncancerous, an external ethmoidectomy may be performed by a surgeon. For this surgery, you can anticipate a small incision on the upper side of your nose near your upper eyelid. By removing a small part of the bone that is part of your orbital bones, your surgeon will be able to remove the tumor.

If the tumor has spread into the ethmoid sinus cavity, the base of the skull, or to the brain, your surgical team will involve both an otolaryngologist and a neurosurgeon due to the ethmoid's crista galli anchoring tissue that surrounds the brain as well as the risk for neurological issues if complications occur. This surgery is referred to as craniofacial resection.

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Bell DJ, Jones J. Labyrinth of ethmoid bone. Radiopaedia.

  2. Cappello ZJ, Minutello K, Dublin AB. Anatomy, Head and Neck, Nose Paranasal Sinuses. [Updated 2020 Sep 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-.

  3. Cedars-Sinai. Sinus Conditions & Treatments.

  4. Nguyen M, Koshy JC, Hollier LH Jr. Pearls of nasoorbitoethmoid trauma managementSemin Plast Surg. 2010;24(4):383-388. doi:10.1055/s-0030-1269767

  5. Ha YI, Kim SH, Park ES, et al. Approach for naso-orbito-ethmoidal fractureArch Craniofac Surg. 2019;20(4):219-222. doi:10.7181/acfs.2019.00255

  6. Harvard Health Publishing. Harvard Medical School. Acute Sinusitis. Jan 2019.

  7. Harvard Health Publishing, Harvard Health. Deviated Septum. May 2019.

  8. American Cancer Society. Key Statistics About Nasal Cavity and Paranasal Sinus Cancers. Revised: April 19, 2021.

  9. American Cancer Society. Survival Rates for Nasal and Paranasal Cancers. Apr 19, 2021.

  10. Brook I. Microbiology of sinusitis. Proc Am Thorac Soc. 2011 Mar;8(1):90-100. doi:10.1513/pats.201006-038RN

  11. Brook I. Acute Sinusitis. Antimicrobe.

  12. American Academy of Allergy Asthma & Immunology. Nasal Polyps. June 28, 2019.

  13. American Cancer Society. Who treats nasal cavity and paranasal sinus cancers?

  14. American Cancer Society. Surgery for Nasal Cavity and Paranasal Sinus Cancers.

Additional Reading