Posterior ethmoidal foramen

Structure

The ethmoid bone is a spongy, irregularly shaped bone located in the midline of the skull, between the orbits (eye sockets) and the nasal cavity. It is composed of several small, thin plates known as lamellae, which are arranged in a honeycomb pattern. Within the ethmoid bone, there are several foramina (openings) that allow for the passage of various structures. The posterior ethmoidal foramen is one of these openings. The posterior ethmoidal foramen is located on the medial (inner) aspect of the orbital plate of the ethmoid bone, near the sphenoid bone. It is situated at the level of the second and third frontal (forehead) convolutions, and is posterior (behind) to the middle ethmoidal foramen. The foramen is surrounded by a bony margin, and is oval in shape. It measures approximately 4-6 mm in diameter.^[3]

Location

The posterior ethmoidal foramen is located within the skull, in the ethmoid bone.^[1] Specifically, it is found on the medial aspect of the orbital plate of the ethmoid bone, near the sphenoid bone. It is located at the level of the second and third frontal convolutions, and is posterior to the middle ethmoidal foramen.^[8]

Function

The posterior ethmoidal foramen serves as a passageway for several important structures within the head. These structures include the following:

• Posterior ethmoidal nerve: This nerve is a branch of the ophthalmic division of the trigeminal nerve (CN V1).^[6] It supplies sensation to the skin of the medial aspect of the orbit (eye socket) and the nasal cavity.
• Posterior ethmoidal artery: This artery is a branch of the ophthalmic artery, which is the first branch of the internal carotid artery. It supplies blood to the nasal cavity, ethmoid sinuses, and orbit.^[7]
• Posterior ethmoidal vein: This vein is a tributary of the superior ophthalmic vein, which drains blood from the orbit.

Clinical Significance

There are several conditions that can affect the posterior ethmoidal foramen and the structures that pass through it.^[4]These conditions include the following:

• Ethmoid sinusitis: This is an infection of the ethmoid sinuses, which are located within the ethmoid bone. Ethmoid sinusitis can cause inflammation and swelling of the mucous membranes lining the sinuses, which can lead to blockage of the posterior ethmoidal foramen. This can lead to pain and discomfort in the orbit and nasal cavity, as well as reduced sense of smell.
• Trauma: The posterior ethmoidal foramen can be damaged by trauma to the head, such as a blow to the face or a car accident. This can result in damage to the posterior ethmoidal nerve, artery, and vein, leading to sensory and vascular abnormalities in the orbit and nasal cavity.^[2]
• Tumors: Tumors can grow within the ethmoid bone and cause pressure on the posterior ethmoidal foramen. This can lead to compression of the structures passing through the foramen, resulting in sensory and vascular abnormalities in the orbit and nasal cavity.
• Aneurysms: An aneurysm is a bulge or ballooning in a blood vessel due to a weakness in the vessel wall. The posterior ethmoidal artery is vulnerable to aneurysm formation due to its location within the skull. If an aneurysm ruptures, it can cause bleeding within the skull, which can be life-threatening.