Posterior ethmoidal artery

The posterior ethmoidal artery is a small branch of the ophthalmic artery that provides blood to the posterior ethmoidal air cells, the sphenoidal sinus, and parts of the nasal cavity. It plays an important role in supplying oxygenated blood to the structures within the ethmoid and sphenoid bones.

Location

The posterior ethmoidal artery arises from the ophthalmic artery as it travels through the orbit. It runs medially along the superior border of the orbit and exits the orbital cavity via the posterior ethmoidal foramen, a small opening in the medial wall of the orbit. After passing through this foramen, the artery enters the posterior ethmoidal air cells and continues into the sphenoidal sinus. Additionally, it provides blood to the dura mater of the anterior cranial fossa.

Structure and Anatomy

The posterior ethmoidal artery is a small but essential branch of the ophthalmic artery, supplying critical structures within the ethmoid bone and sphenoid sinus, as well as contributing to the blood supply of the dura mater. Below is a detailed description of its anatomy.

Origin

The posterior ethmoidal artery originates from the ophthalmic artery, which is itself a branch of the internal carotid artery. The ophthalmic artery enters the orbit through the optic canal and gives rise to several branches, including the posterior ethmoidal artery. This artery typically branches from the ophthalmic artery at a slightly more posterior point than the anterior ethmoidal artery.

Course

• Intraorbital Segment:After originating from the ophthalmic artery within the orbit, the posterior ethmoidal artery travels medially along the medial wall of the orbit, closely related to the orbital periosteum. It courses superior to the medial rectus muscle, which controls the movement of the eye, but does not directly supply it.
• Passage Through the Posterior Ethmoidal Foramen:The posterior ethmoidal artery exits the orbit through the posterior ethmoidal foramen, a small opening located on the medial orbital wall. This foramen is found in the junction between the frontal and ethmoid bones. The foramen serves as a conduit for the artery to leave the orbit and enter the ethmoidal labyrinth.
• Ethmoidal Segment (Posterior Ethmoidal Air Cells):After passing through the posterior ethmoidal foramen, the artery enters the posterior ethmoidal air cells, which are small air-filled cavities located within the ethmoid bone. In this region, the artery provides blood to the mucosa that lines these air cells, ensuring adequate oxygenation and nourishment of the sinus tissues.
• Sphenoidal Segment (Sphenoidal Sinus):As the posterior ethmoidal artery continues its course, it extends into the sphenoidal sinus, one of the major paranasal sinuses located within the body of the sphenoid bone. The artery helps supply blood to the mucosal lining of the sphenoidal sinus.
• Cranial Segment (Anterior Cranial Fossa):Before or during its course through the ethmoid bone, the posterior ethmoidal artery gives off small branches to the dura mater in the anterior cranial fossa. The dura mater is the outermost membrane that covers the brain, and this arterial supply contributes to its vascularization, specifically overlying the frontal lobes of the brain.

Branches of the Posterior Ethmoidal Artery

• Ethmoidal Branches:As the posterior ethmoidal artery passes through the posterior ethmoidal air cells, it gives off several small branches that supply blood to the mucosa lining these air cells. The mucosa plays a role in humidifying and warming inhaled air, and the artery’s branches ensure that this tissue remains healthy.
• Sphenoidal Branches:The posterior ethmoidal artery also gives off branches to the sphenoidal sinus, one of the four major paranasal sinuses. These branches supply the mucosal lining of the sphenoidal sinus, which is involved in respiratory functions like conditioning the air before it enters the lungs.
• Meningeal Branches:Before entering the nasal region, the posterior ethmoidal artery provides small meningeal branches that supply the dura mater covering the anterior cranial fossa. This region houses the frontal lobes of the brain, and the artery’s contribution to its vascularization is important for maintaining the integrity of the brain’s protective coverings.

Anatomical Relations

• Medial Rectus Muscle:As the posterior ethmoidal artery courses through the orbit, it runs superior to the medial rectus muscle, which controls the inward movement of the eye. Although the artery does not supply the muscle directly, it travels in close proximity to this structure as it approaches the posterior ethmoidal foramen.
• Ethmoid Bone:The posterior ethmoidal artery passes through the ethmoid bone, one of the most complex bones in the skull, which forms part of the nasal cavity and contains the ethmoidal air cells. The artery provides blood to the posterior ethmoidal air cells, which are located within this bone.
• Sphenoid Bone and Sinus:After supplying the ethmoidal air cells, the artery continues to the sphenoidal sinus, located within the sphenoid bone. The sphenoid bone forms the central base of the skull, and the sphenoidal sinus, located within this bone, is an important structure for air filtration and drainage into the nasal cavity.
• Dura Mater and Anterior Cranial Fossa:Before entering the ethmoidal air cells, the posterior ethmoidal artery gives off small branches to the dura mater, the outer protective covering of the brain. These branches supply the dura mater located in the anterior cranial fossa, the bony depression that supports the frontal lobes of the brain.

Termination

The posterior ethmoidal artery terminates by distributing its branches to the posterior ethmoidal air cells, the sphenoidal sinus, and the dura mater of the anterior cranial fossa. Its branches ensure that these regions receive adequate blood supply to support their respiratory and protective functions.

Variability

The posterior ethmoidal artery typically originates from the ophthalmic artery within the orbit, but its exact course and branching pattern can vary between individuals. It is often smaller than the anterior ethmoidal artery, reflecting its role in supplying the smaller, posterior regions of the ethmoid and sphenoid bones. In some individuals, there may be anatomical variations in the size or number of branches that the posterior ethmoidal artery provides to the sphenoid sinus or dura mater.

Function

The posterior ethmoidal artery is an essential blood vessel that supports critical functions in the paranasal sinuses, nasal cavity, and cranial meninges. Below is a detailed explanation of its functions based on the regions it supplies.

Blood Supply to the Posterior Ethmoidal Air Cells

Nourishment of the Posterior Ethmoidal Air Cells

• The posterior ethmoidal artery supplies blood to the posterior ethmoidal air cells, which are part of the ethmoid bone’s sinus system. These air cells are responsible for filtering and humidifying the air before it passes through the nasal cavity.
• By delivering oxygenated blood to the mucosal lining of these air cells, the artery ensures that the tissues remain healthy and functional. The blood flow supports the production of mucus that traps dust, pathogens, and other particles, contributing to respiratory health.

Support for Humidification and Filtration of Inhaled Air

The posterior ethmoidal air cells play an essential role in humidifying and warming inhaled air. The blood supply provided by the posterior ethmoidal artery supports this process, ensuring that the air reaching the lower respiratory tract is conditioned properly, reducing irritation to the lungs and trachea.

Blood Supply to the Sphenoidal Sinus

Nourishment of the Sphenoidal Sinus

• The posterior ethmoidal artery supplies the sphenoidal sinus, one of the major paranasal sinuses located within the sphenoid bone. The mucosa of the sphenoidal sinus is responsible for producing mucus that helps cleanse and moisten the air we breathe.
• By providing a steady blood supply to the mucosa, the artery ensures the proper functioning of the sinus, supporting the mucous production necessary for protecting the respiratory system from pollutants and pathogens.

Support for Sinus Drainage

The sphenoidal sinus drains into the nasal cavity, and the health of this drainage system depends on proper vascularization. The posterior ethmoidal artery’s supply to the sphenoidal sinus ensures that the sinus remains healthy, which aids in the efficient drainage of mucus and prevents sinus infections or blockages.

Blood Supply to the Nasal Cavity and Posterior Septum

Contribution to the Nasal Septum and Lateral Nasal Wall

• Although the posterior ethmoidal artery primarily supplies the ethmoidal and sphenoidal sinuses, it also contributes blood to the posterior nasal septum and the lateral nasal wall. This helps in maintaining the integrity of the nasal mucosa, which filters and conditions the air as it moves through the nasal passages.
• The blood flow ensures the mucosa remains healthy, protecting the nasal cavity from dryness and irritation. Additionally, it aids in maintaining the function of the olfactory epithelium, which is involved in the sense of smell.

Blood Supply to the Dura Mater

Vascularization of the Anterior Cranial Fossa

• The posterior ethmoidal artery gives off small branches to the dura mater in the anterior cranial fossa, which covers the frontal lobes of the brain. The dura mater is the outermost membrane of the meninges, which protect and support the brain.
• The artery’s blood supply helps maintain the health and integrity of the dura mater, ensuring that this protective layer receives the nutrients and oxygen it needs to function properly. This is essential for preventing damage or inflammation to the brain’s protective coverings.

Support for Meningeal Function

The dura mater requires a continuous blood supply to maintain its structural integrity and support its function in protecting the brain from injury and infection. By nourishing the dura mater, the posterior ethmoidal artery helps preserve the meninges’ ability to cushion and support the brain during movement, maintaining the brain’s stability within the skull.

Role in Immune Response and Respiratory Health

Support for Immune Defense in the Sinuses

• The mucosa lining the ethmoidal and sphenoidal sinuses contains immune cells, such as lymphocytes and macrophages, that help protect the body from infections by capturing and neutralizing pathogens. The posterior ethmoidal artery ensures that these cells receive the necessary nutrients and oxygen to function effectively.
• By supporting the immune response within the sinuses, the artery helps the body maintain its defenses against respiratory infections and airborne pathogens.

Facilitation of Mucociliary Clearance

• The mucosa in the sinuses and nasal cavity is lined with cilia, tiny hair-like structures that move mucus and trapped particles toward the pharynx, where they can be swallowed or expelled. The posterior ethmoidal artery provides the blood supply that keeps these ciliated cells healthy and functional.
• This process, known as mucociliary clearance, is essential for maintaining clean and healthy airways. By ensuring proper blood flow to the sinuses, the artery supports this vital respiratory function.

Clinical Significance

The posterior ethmoidal artery plays an important role in supplying blood to the posterior ethmoidal air cells, sphenoidal sinus, and parts of the dura mater. Its clinical significance arises from its involvement in certain medical conditions and surgical procedures. Damage or rupture of the posterior ethmoidal artery during endoscopic sinus surgery, particularly when operating in the ethmoidal and sphenoidal regions, can result in significant bleeding and may lead to complications involving the anterior cranial fossa and the brain’s protective layers.

The artery also contributes to the vascularization of the nasal cavity and can be involved in cases of epistaxis (nosebleeds) originating from the posterior nasal regions, although it is less commonly associated with epistaxis than arteries in the anterior nasal region. In cases of severe trauma or fractures involving the ethmoid bone or orbit, the posterior ethmoidal artery may be compromised, potentially leading to hemorrhage or ischemia of the sinus tissues.

Additionally, the artery’s branches to the dura mater may be implicated in conditions such as meningitis or inflammatory disorders, where inflammation of the meninges occurs. Given its proximity to both the paranasal sinuses and cranial cavity, the posterior ethmoidal artery is a critical structure in both respiratory and neurological health.