The Anatomy of the Ethmoid Bone

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The ethmoid bone is one of the most complex bones of your face and is located in the center of your skull between your eyes. The ethmoid bone is only about the size of an ice cube but is very light and sponge-like in appearance that helps to form the walls of your eye socket, or orbital cavity, as well as the roof, sides, and interior of your nasal cavity.

Anatomy

The ethmoid bone is made up of 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, which includes: maxillary, frontal, ethmoid, 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 (falx cerebri) that surrounds your brain, anchoring it into place.

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

Function

Because the ethmoid bone is a complex bony structure that is centrally located in your face, it has various functions that it has to support some common everyday activities that you enjoy. The cribriform plate has sieve-like holes that allow the olfactory nerves to locate in your nose so that you can experience your sense of smell, and also plays a role in your ability to taste.

Sinus cavities which are contained in the ethmoidal labyrinth help to 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
  • lighten the head

The nasal conchae that the ethmoid forms allows airflow 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 as well which 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 is a lot of blood vessels in this area, severe nose bleeds (epistaxis) usually occurs with an NOE fracture. Other symptoms associated with an NOE fracture include:

  • overflowing tears
  • ocular injury
  • abnormal distance between 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 may include pain (behind and between the eyes and sides of the nose), a "splitting headache" (a headache that occurs at the front of your head), periorbital cellulitis (a skin infection around your eye, particularly your eyelids), tearing or watery eyes and/or a loss of smell (olfactory dysfunction).

You may also experience pain similar to ethmoid sinusitis if you have an overabundance of polyps (abnormal non-cancerous growths) in your ethmoid sinus cavity. Symptoms related to this would be the same pain behind or between the eyes, however, you may experience this more commonly when diving, flying, or a general change in altitude or pressure.

Polyps, like sinusitis, is another common cause for loss of your sense of smell.

A deviated septum may involve part of the perpendicular plate which forms the upper part of the nasal septum. Depending on the severity of the deviated septum, you may not notice any symptoms. However, more severe cases may cause nose bleeds and difficulty breathing through one of your nares.

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, 85 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 44 to 50 out of 100 people will make it to more than five years of survival.

Treatment

If you suffer trauma to the face and have symptoms of NOE fracture described above, 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. Beyond surgery, other follow-up care such as an eye exam may be required.

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 even without a positive culture:

  1. You have mild to moderate symptoms lasting greater than or equal to 10 days.
  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 it is determined to start you on antibiotics, a first line choice is often amoxicillin/clavulanate. Typically you will be given 875 mg (or 25 milligrams per kilogram in children) every 12 hours. However, if you are thought to have antibiotic resistance, doses may be escalated up to 2 grams (or 45 milligrams per kilogram in children) every 12 hours.

A CT scan may be used in determining sinus infection, but often treatment is determined by clinical exam.

However, if your doctor is concerned that polyps are the underlying cause of your symptoms, a 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. Member of your interdisciplinary team may include:

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

If the tumor is small and/or non-cancerous, 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 connective tissue that surrounds the brain as well as the risk for neurological complications if complications occur. This surgery is referred to as craniofacial resection.

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