Pterygoid plexus

The pterygoid plexus is a dense network of interconnected veins located in the infratemporal fossa of the skull. It is situated between the lateral and medial pterygoid muscles, near the pterygoid plates of the sphenoid bone. The plexus receives blood from multiple areas, including the face, orbit, nasal cavity, and oral cavity, and is an important component of venous drainage in the head.

Location

The pterygoid plexus is located in the infratemporal fossa, a space situated below the base of the skull and behind the maxilla. It lies between the medial and lateral pterygoid muscles and is close to other important structures such as the maxillary artery and mandibular nerve. The plexus connects with several veins, including the facial vein, deep facial vein, and the maxillary vein.

Structure and Anatomy

Structure

The pterygoid plexus is composed of multiple venous channels that interconnect, forming a highly anastomosed venous network.

Boundaries

• Superiorly: The pterygoid plexus is bordered by the greater wing of the sphenoid bone.
• Medially: It is adjacent to the medial pterygoid muscle.
• Laterally: It is bordered by the lateral pterygoid muscle.
• Anteriorly: The plexus is located near the posterior aspect of the maxilla.
• Posteriorly: It extends toward the mandibular ramus.

Tributaries

The pterygoid plexus receives blood from several regions of the head and face, making it a significant structure for venous drainage. Its tributaries include:

• Deep facial vein: Drains blood from the face, particularly the infraorbital region, and communicates with the pterygoid plexus.
• Maxillary vein: One of the main venous channels draining into the pterygoid plexus. It forms a significant part of the venous outflow from the plexus.
• Sphenopalatine vein: Drains the nasal cavity and connects to the pterygoid plexus, facilitating venous drainage from the nasal region.
• Inferior ophthalmic vein: Drains blood from the orbit and connects to the pterygoid plexus, forming an important pathway for venous return from the eye.
• Muscular branches: Veins from the masticatory muscles, such as the masseter, temporalis, and the pterygoid muscles, drain into the pterygoid plexus.

Connections to Other Venous Systems

The pterygoid plexus serves as a communication point between several important venous systems in the head. These connections include:

• Facial vein: Through the deep facial vein, the pterygoid plexus communicates with the facial vein, which drains the superficial structures of the face.
• Cavernous sinus: The pterygoid plexus connects to the cavernous sinus, located within the cranial cavity, through small emissary veins. This connection provides a potential route for venous blood to travel between the cranial cavity and the infratemporal fossa.
• Pharyngeal plexus: The pterygoid plexus also communicates with the pharyngeal plexus, which drains the pharyngeal region.

Outflow

The venous blood from the pterygoid plexus is eventually drained into the maxillary vein, which continues into the retromandibular vein. The retromandibular vein further drains into the external jugular vein, facilitating the return of venous blood to the heart through the subclavian vein.

Surrounding Structures

• Maxillary Artery: The maxillary artery, one of the terminal branches of the external carotid artery, runs close to the pterygoid plexus. Several branches of the maxillary artery are in close proximity, including the deep temporal arteries and the inferior alveolar artery.
• Mandibular Nerve (V3): The mandibular branch of the trigeminal nerve (cranial nerve V) passes near the pterygoid plexus, providing motor innervation to the muscles of mastication and sensory innervation to parts of the face.
• Temporomandibular Joint (TMJ): The plexus is located near the temporomandibular joint, and its position in the infratemporal fossa places it in close proximity to the joint capsule.

Variations

The anatomy of the pterygoid plexus can vary between individuals in terms of the number of veins and the extent of the venous network. Some individuals may have more prominent communications between the pterygoid plexus and the facial or ophthalmic veins, while others may have fewer connections. The overall size and complexity of the venous network can also differ.

Emissary Veins

The pterygoid plexus is connected to the cavernous sinus via small emissary veins. These emissary veins allow blood to flow between the extracranial and intracranial venous systems, providing a direct route between the pterygoid plexus and the cavernous sinus. This connection also serves as a potential route for the spread of infections from the face to the cranial cavity.

Relation to the Parotid Gland

Although not directly involved in the venous drainage of the parotid gland, the pterygoid plexus is located close to the posterior border of the parotid gland. This proximity places the plexus in a strategic position between the parotid gland and the infratemporal fossa.

Function

Venous Drainage of the Infratemporal Region

The primary function of the pterygoid plexus is to facilitate venous drainage from the infratemporal fossa, a deep area of the face. This region includes important structures such as the pterygoid muscles, temporalis muscle, masseter muscle, and other muscles of mastication. The plexus collects deoxygenated blood from these muscles, ensuring the proper removal of metabolic waste products and maintaining efficient blood circulation in the area.

Drainage of the Deep Facial Veins

The pterygoid plexus plays a significant role in draining blood from the deep facial structures, including:

• Deep facial vein: Drains blood from the midface, including the maxillary region, upper jaw, and infraorbital area. The deep facial vein connects to the pterygoid plexus, allowing blood from these areas to be routed toward larger veins.
• Sphenopalatine veins: Drains the nasal cavity and palate, ensuring venous return from the nasal region into the pterygoid plexus. The plexus acts as a collecting system for blood from these deeper regions, providing a network that integrates venous flow from multiple parts of the head.

Connection with the Maxillary Vein

The pterygoid plexus serves as an intermediary for venous drainage into the maxillary vein. After collecting venous blood from the deep facial regions and muscles of mastication, the plexus channels the blood into the maxillary vein. This vein is a major outflow pathway that eventually drains into the retromandibular vein, which joins the external jugular vein and transports the blood back toward the heart. This function ensures the continuous removal of blood from the deep facial regions to the central venous system.

Regulation of Venous Pressure

Due to its extensive network of interconnected veins, the pterygoid plexus helps regulate venous pressure in the face and deep structures of the head. The plexus can adapt to changes in pressure, accommodating blood flow under different physiological conditions, such as during chewing or talking, when the muscles of mastication are highly active. This regulatory function is important in maintaining a stable venous flow and preventing venous congestion in the facial regions.

Communication with the Cavernous Sinus

One of the most important functions of the pterygoid plexus is its communication with the cavernous sinus, a large venous sinus located within the cranial cavity. The pterygoid plexus connects to the cavernous sinus via emissary veins, providing an alternative route for venous blood to flow between the extracranial and intracranial regions. This connection is part of a broader collateral circulation network that allows blood to be rerouted in case of blockages or increased pressure within the cranial venous system. The emissary veins also enable the venous blood from the orbit and deeper facial structures to drain via the pterygoid plexus when necessary.

Facilitation of Collateral Circulation

The pterygoid plexus provides a critical role in collateral circulation by connecting several major venous pathways in the head and neck, including:

• Facial vein: The pterygoid plexus is connected to the superficial facial venous system via the deep facial vein, offering an alternative route for blood to drain from the face.
• Inferior ophthalmic vein: This vein drains the orbital region and can empty into the pterygoid plexus, providing venous drainage from the eye and orbit in addition to its other connections to the cavernous sinus.
• Pharyngeal plexus: The pterygoid plexus communicates with the pharyngeal venous plexus, helping facilitate drainage from the pharynx and adjacent areas of the neck.

This network of connections allows the pterygoid plexus to act as a hub for rerouting venous blood, maintaining efficient venous return even when other pathways are compromised, such as during trauma, surgery, or venous obstructions.

Absorption of Pressure During Mastication

During mastication (chewing), the muscles of mastication (temporalis, masseter, and pterygoid muscles) exert mechanical forces on the surrounding tissues, which could potentially impede venous flow. The pterygoid plexus absorbs these pressure changes by providing a large, flexible venous network that can expand to accommodate increased blood flow. This helps ensure that venous blood from the muscles of mastication is efficiently drained, even when these muscles are highly active. This absorption of pressure also prevents venous congestion and maintains normal venous circulation during activities that place stress on the facial muscles.

Drainage from the Nasal Cavity and Orbit

In addition to its role in draining blood from the deep facial muscles, the pterygoid plexus also assists in venous return from other key areas of the head, including:

• Nasal cavity: The plexus receives venous blood from the sphenopalatine vein, which drains the nasal cavity and the paranasal sinuses. This ensures the removal of blood from the nasal region and prevents the buildup of pressure in the sinuses.
• Orbit: The inferior ophthalmic vein can drain into the pterygoid plexus, providing an alternative route for venous blood from the orbit to exit the cranial cavity.

This ability to receive blood from multiple regions enhances the role of the pterygoid plexus as a versatile venous network, ensuring efficient drainage from several vital areas of the head.

Communication with the Pharyngeal Plexus

The pterygoid plexus also connects with the pharyngeal venous plexus, facilitating the drainage of blood from the pharynx and surrounding structures. This connection ensures that venous return from the pharyngeal area is well-regulated and helps in preventing venous congestion within the soft tissues of the neck and pharynx.

Clinical Significance

The pterygoid plexus plays an important role in venous drainage from the face, deep facial structures, and cranial cavity, making it clinically significant in several contexts. Due to its connections with the cavernous sinus via emissary veins, the pterygoid plexus can act as a pathway for the spread of infections from the face to the brain, potentially leading to life-threatening conditions like cavernous sinus thrombosis.

Additionally, the plexus is vulnerable to injury during dental procedures, particularly during the extraction of upper molars or surgeries involving the maxilla. Hemorrhage from the pterygoid plexus may occur if it is damaged, which can be difficult to control due to the plexus’s complex and highly anastomosed structure. Its extensive connections to the venous systems of the orbit, nasal cavity, and pharynx make it relevant in various surgical and pathological conditions in the head and neck region.