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Pterygoid plexus

The pterygoid plexus is a valveless network of interconnected veins located in the infratemporal fossa of the skull, serving as a primary drainage pathway for blood from the nasal cavity, paranasal sinuses, nasopharynx, and adjacent structures in the head.^[1] Positioned between the medial and lateral pterygoid muscles and in close association with the maxillary artery, the plexus facilitates venous return through a pumping mechanism driven by contractions of the lateral pterygoid muscle during jaw movement.^[1]^[2] Key tributaries to the pterygoid plexus include the superior and inferior alveolar veins, sphenopalatine vein, descending palatine vein, infraorbital vein, posterior superior alveolar vein, anterior and posterior deep temporal veins, middle meningeal vein, masseteric vein, buccal vein, and inferior alveolar vein, collectively draining regions such as the meninges, infratemporal fossa, and oral cavity.^[1]^[2] The plexus primarily drains posteriorly via the maxillary vein, which joins the superficial temporal vein to form the retromandibular vein and ultimately contributes to the external jugular vein.^[1] It also maintains extensive communications with surrounding venous structures, including the facial vein through the deep facial vein, the inferior ophthalmic vein via the inferior orbital fissure, and the cavernous sinus through emissary veins passing via the foramen ovale and foramen Vesalius, as well as connections to the pharyngeal venous plexus.^[1]^[3]^[2] Clinically, the pterygoid plexus's valveless design and direct linkage to the cavernous sinus enable bidirectional blood flow but increase the risk of retrograde infection spread from facial or oral sources, potentially resulting in cavernous sinus thrombosis with complications such as cranial nerve palsies (affecting nerves III, IV, V1, V2, and VI) or central nervous system involvement.^[1]^[3] Additionally, inadvertent puncture of the plexus during procedures like posterior superior alveolar nerve blocks can lead to hematoma formation.^[1]

Anatomy

Location and Composition

The pterygoid plexus is defined as a complex network of interconnected veins situated within the infratemporal fossa of the skull, primarily surrounding the lateral pterygoid muscle and the pterygoid portion of the maxillary artery.^[1]^[4] This venous structure occupies a space bordered anteriorly by the posterior surface of the maxilla, posteriorly by the tympanic plate and styloid process, laterally by the ramus of the mandible, medially by the lateral pterygoid plate of the sphenoid bone, inferiorly by the attachment of the medial pterygoid muscle to the medial ramus surface, and superiorly by the infratemporal surface of the greater wing of the sphenoid bone.^[1]^[5] As such, the plexus typically extends vertically from the base of the skull to the level of the mandibular ramus, filling much of the infratemporal fossa's depth.^[1] In terms of gross anatomy, the pterygoid plexus comprises numerous small, interconnecting veins that form a diffuse, three-dimensional network rather than a unified trunk, paralleling the branches of the maxillary artery within the fossa.^[1]^[4] It lies partly deep to the lower head of the lateral pterygoid muscle and between the temporal and pterygoid muscles superiorly, as well as between the medial and lateral pterygoid muscles inferiorly, embedded amid the loose areolar tissue of the region.^[4]^[5] The overall configuration lacks prominent valves in its primary channels, contributing to its role as a low-pressure collecting system.^[6]

Tributaries

The pterygoid plexus, situated within the infratemporal fossa, receives venous drainage from multiple tributaries that parallel the branches of the maxillary artery, collecting blood from adjacent muscles, dental structures, and soft tissues.^[1] These tributaries form a network that ensures efficient drainage from the masticatory apparatus and surrounding areas.^[7] The deep temporal veins are prominent tributaries originating from the deep surface of the temporalis muscle, where they accompany the deep temporal arteries and converge to enter the anterior aspect of the pterygoid plexus.^[4] Typically, anterior and posterior deep temporal veins are distinguished, with the posterior pair draining the posterior temporalis and joining near the muscle's insertion.^[7] Pterygoid veins arise directly from the venous drainage of the medial and lateral pterygoid muscles, forming small channels that intertwine with the plexus around the lateral pterygoid muscle in the infratemporal fossa.^[1] These veins provide essential outflow for the masticatory muscles, with their origins embedded within the muscle bellies. The masseteric vein collects blood from the masseter muscle, traveling alongside the masseteric artery to unite with the pterygoid plexus laterally.^[7] This tributary is consistent in its contribution to the venous network supporting jaw elevation.^[1] Posterior superior alveolar veins drain the upper molar and premolar teeth and associated gingiva, emerging from the alveolar processes to join the posterior portion of the plexus.^[7] These veins accompany the posterior superior alveolar arteries through foramina in the maxilla.^[1] The inferior alveolar vein originates from the lower teeth and mandible, coursing through the mandibular canal with the inferior alveolar artery and nerve before emptying into the pterygoid plexus medially.^[7] It provides drainage for the mandibular dental arch and associated structures.^[1] Buccal veins drain the buccal mucosa and cheek region, passing superficially through the buccinator muscle to connect with the plexus.^[1] These veins often accompany the buccal artery and contribute to the overall facial venous return.^[1] Sphenopalatine vein drains the nasal cavity and joins the plexus.^[7] Descending palatine vein (also known as greater palatine vein) drains the palate and hard palate region.^[4] Infraorbital vein drains the infraorbital region and lower eyelid area.^[7] Middle meningeal vein drains the dura mater and enters the plexus, providing a connection between intracranial and extracranial venous systems.^[7] Tributary patterns exhibit variability across individuals, including occasional direct communications from other regional veins. Such variations are noted in anatomical dissections but do not alter the primary drainage role of the core tributaries.^[1]

Anastomoses and Drainage

The pterygoid venous plexus primarily drains posteriorly through the maxillary vein, which unites with the superficial temporal vein to form the retromandibular vein; the retromandibular vein then bifurcates, with its anterior division joining the common facial vein to drain into the internal jugular vein, while its posterior division contributes to the external jugular vein.^[1]^[8] This pathway integrates the plexus into the broader extracranial venous network, facilitating the return of venous blood from the infratemporal fossa to the central venous system.^[1] Key anastomoses of the pterygoid plexus include connections with the cavernous sinus via emissary veins passing through the foramen ovale, as well as the vein of Vesalius through the foramen of Vesalius when present.^[1]^[8] It also anastomoses with the facial vein through the deep facial vein, allowing bidirectional exchange between extracranial facial drainage and the pterygoid network.^[1]^[8] The plexus communicates with the pharyngeal venous plexus, providing a pathway for venous return from pharyngeal structures, and with the ophthalmic veins via the inferior ophthalmic vein through the inferior orbital fissure, which can enable potential retrograde flow under certain conditions.^[1] The absence of valves in the pterygoid plexus veins permits this bidirectional flow, directing primary outflow toward the internal jugular vein while preventing significant backflow through coordinated muscular compression during jaw movement.^[1]

Relations to Surrounding Structures

The pterygoid plexus occupies a central position within the infratemporal fossa, bordered superiorly by the temporalis muscle, medially by the medial pterygoid muscle, and laterally by the mandibular ramus.^[1] This venous network lies in close proximity to the lateral pterygoid muscle, positioning superficially to its fibers while intermingling with them, which facilitates interactions during masticatory movements.^[1] The plexus also relates to the branches of the mandibular nerve (cranial nerve V3), which traverse the fossa after emerging from the foramen ovale, with some venous tributaries paralleling these neural structures.^[1] The maxillary artery passes through the infratemporal fossa in intimate relation to the pterygoid plexus, with the second (pterygoid) portion of the artery embedded within and surrounded by the venous network, allowing for shared pathways with its branches.^[10] Additionally, the plexus maintains positional relations to key foramina in the greater wing of the sphenoid bone, including the foramen ovale and foramen spinosum; emissary veins traverse the foramen ovale to connect the plexus to the cavernous sinus, while the middle meningeal vein links it via the foramen spinosum, providing potential extracranial-intracranial communications.^[1] The pterygoid plexus interacts with the sphenomandibular ligament, as the maxillary vein—formed by coalescence of the plexus—courses posteriorly between this ligament and the mandibular neck, influencing the spatial constraints in the medial aspect of the fossa.^[10] Furthermore, the plexus is embedded within the loose areolar connective tissue and adjacent fascia of the infratemporal fossa, which envelops the surrounding masticatory muscles and neurovascular elements, thereby defining boundaries for surgical approaches to the region.^[11]

Function

Mechanism of Venous Drainage

The mechanism of venous drainage in the pterygoid plexus relies on a biomechanical pumping action generated by contractions of the lateral pterygoid muscle, which surrounds and compresses the plexus to propel blood posteriorly toward the maxillary vein. This muscular compression mimics a peripheral pump, facilitating the return of deoxygenated blood in the low-pressure venous system.^[12]^[1] The valveless veins within the plexus allow bidirectional flow, directing blood primarily toward the maxillary vein for eventual drainage into the retromandibular vein. These work in concert with the muscle-induced compression to maintain efficient forward propulsion. Additionally, muscle activity during contractions establishes localized pressure gradients that overcome the inherent low pressure of venous return, compensating for the absence of arterial pulsations.^[12] Jaw movements, such as mastication and yawning, drive cyclic compression and decompression of the plexus through repeated contractions of the lateral pterygoid muscle. During mastication, the coordinated action of masticatory muscles enhances drainage by rhythmically squeezing the venous network. Similarly, yawning involves significant jaw opening mediated by the lateral pterygoid, promoting plexus expansion and subsequent blood propulsion upon relaxation. The plexus maintains anastomotic connections to the cavernous sinus via emissary veins.^[11]^[13]

Role in Head and Neck Circulation

The pterygoid plexus integrates into the valveless venous network of the head and neck, serving as a critical conduit that connects extracranial and intracranial circulations through emissary veins. Specifically, it communicates with the cavernous sinus via an emissary vein passing through the foramen ovale, allowing bidirectional flow between the deep facial veins and the dural venous sinuses without valvular restriction. This arrangement facilitates the exchange of venous blood between superficial and deep compartments, contributing to the overall efficiency of cerebral and facial venous drainage.^[1]^[14] In scenarios of obstruction in major veins such as the internal jugular, the pterygoid plexus supports collateral drainage pathways, primarily by emptying into the maxillary vein, which joins the retromandibular vein and ultimately the external jugular vein. This collateral route helps maintain venous return from the head and neck when primary pathways are compromised, preventing potential venous hypertension in the intracranial compartment. The plexus's connections thus enhance circulatory resilience in the region.^[1]^[15] The pterygoid plexus plays a vital role in supporting venous return from deep facial structures, including the nasal cavity, paranasal sinuses, nasopharynx, and infratemporal fossa, as well as from surrounding muscles like the pterygoids and indirectly from the meninges via dural sinus linkages. By efficiently channeling this blood toward the heart, it helps prevent venous stasis in these enclosed spaces, promoting steady circulation and reducing the risk of localized congestion. Muscle contractions, such as those of the lateral pterygoid, assist this drainage process.^[1]^[15] Additionally, the pterygoid plexus contributes to adaptive functions in the head and neck by influencing eustachian tube dynamics through changes in venous volume, which can aid in adjusting middle ear pressures during postural changes.^[16]

Clinical Significance

Risk of Infection Propagation

The pterygoid plexus poses a significant risk for the propagation of infections due to its valveless venous structure, which allows bidirectional flow and facilitates the retrograde spread of pathogens from extracranial sites to intracranial spaces. This plexus communicates with the cavernous sinus through emissary veins passing via the foramen ovale, enabling bacteria or thrombi to disseminate rapidly without valvular barriers impeding progression.^[1] Such connections heighten the vulnerability to severe complications like septic thrombosis when infections originate in adjacent regions.^[17] Odontogenic infections, such as those arising from dental abscesses, commonly exploit the pterygoid plexus as a conduit to the cavernous sinus, potentially leading to life-threatening cavernous sinus thrombosis (CST). Pathogens from untreated dental sources can enter the plexus directly through its proximity to the masticatory muscles and oral cavity, traveling via emissary veins to form infected thrombi in the cavernous sinus. This pathway accounts for a notable portion of septic CST cases, with odontogenic origins implicated in up to 10% of severe instances, emphasizing the need for prompt dental intervention to prevent intracranial extension.^[18]^[1] Infections within the masticator space, often stemming from mandibular or maxillary odontogenic foci, can similarly propagate through the pterygoid plexus to the cranial cavity, bypassing anatomical barriers due to the absence of valves in these venous channels. This spread may result in dural sinus involvement, meningitis, or cerebral abscesses, as the plexus's connections allow direct access to intracranial venous systems. The infratemporal and pterygomandibular subspaces, integral to the masticator region, serve as initial reservoirs where infections accumulate before venous dissemination.^[17]^[1] Case reports illustrate the perilous potential for septic emboli originating from pterygoid plexus infections, including historical examples tied to odontogenic sources. In one instance, a 65-year-old man developed CST from a buccal space abscess linked to a denture-related laceration, with Staphylococcus aureus spreading via the pterygoid plexus, resulting in periorbital edema and visual impairment before resolution with drainage and antibiotics. Another case involved a 50-year-old woman with a maxillary molar abscess that progressed to bilateral CST and a cerebellar abscess, disseminating septic emboli through the valveless plexus and causing ophthalmoplegia and facial palsy, ultimately managed with multidisciplinary therapy. A third report described a 49-year-old man with third molar caries leading to bilateral CST via the plexus from masticator space involvement, complicated by orbital cellulitis and Pseudomonas aeruginosa septicemia. These examples underscore the historical pattern of such emboli causing multifocal intracranial pathology.^[18]^[19]^[20] Contributing factors to this infection risk include the pterygoid plexus's anatomical proximity to the oral cavity, which exposes it to polymicrobial flora from dental procedures or abscesses, and poor oral hygiene, which fosters chronic bacteremia and untreated odontogenic foci conducive to venous invasion. Immunocompromised states or delayed treatment further amplify the likelihood of progression from local infection to systemic septic events via these routes.^[17]^[1]

Implications in Surgery and Procedures

The pterygoid plexus poses a significant risk of hemorrhage during temporomandibular joint (TMJ) surgeries, such as ankylosis release or condylar procedures, due to its proximity to the deep condylar head and potential for disruption by surgical instruments.^[21] In these interventions, injury to the plexus can lead to troublesome, uncontrolled bleeding that is difficult to arrest without advanced hemostatic measures.^[22] Similarly, in maxillary osteotomies like Le Fort I procedures, separation of the pterygomaxillary junction often risks damaging the plexus, resulting in profuse venous bleeding from the infratemporal fossa.^[23] This complication occurs in up to 0.2–2.2% of orthognathic cases, potentially requiring transfusion or conversion to open approaches.^[24] Precautions are essential in endoscopic sinus surgery to avoid plexus injury, particularly during subperiosteal elevation near the pterygoid process or resection of tumors like juvenile nasopharyngeal angiofibroma (JNA), where venous bleeding can obscure visualization.^[25] Surgeons employ meticulous dissection and preoperative imaging to identify venous connections, minimizing inadvertent damage to communicating branches.^[26] In dental extractions, especially of maxillary molars involving aggressive tuberosity removal, care must be taken to prevent penetration into the infratemporal fossa, as this can lacerate the plexus and cause life-threatening hemorrhage.^[6] Management of plexus disruption in infratemporal fossa procedures includes ligation of the maxillary vein to isolate venous outflow and reduce bleeding volume, often performed intraorally or endoscopically for access.^[27] Hemostatic agents such as oxidized cellulose (Surgicel) or gelatin sponges (Gelfoam) are applied to tamponade venous oozing, while bipolar electrocautery targets focal points without spreading current to adjacent nerves.^[28] Packing with vasoconstrictive agents provides temporary control in endoscopic settings.^[29] Postoperative monitoring focuses on detecting hematoma formation through serial clinical exams and imaging, as expanding collections in the infratemporal fossa can compromise airway patency or cause facial swelling.^[30] Vigilance for air embolism is critical due to the plexus's open connections to intracranial veins like the cavernous sinus; symptoms such as sudden neurological changes warrant immediate CT angiography and hyperbaric therapy if confirmed.^[31] Patients are observed in a controlled setting for at least 24–48 hours to identify delayed bleeding or embolic events.^[32]

References

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The pterygoid plexus is a complex of veins located in the infratemporal fossa of the skull with comprehensive connections to surrounding veins and anatomical ...
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The Pterygoid Plexus refers to a network of veins that surrounds the lateral pterygoid muscle. It is important to consider this plexus when performing ...
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unnamed tributaries that drain the pharyngeal wall, internal jugular, pharynx, connects with the pterygoid venous plexus. plexus, pterygoid venous, descending ...
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Mar 7, 1980 · The anterior facial vein anastomoses with the pterygoid plexus via the deep facial vein and with the cavernous sinus via the angular and ...
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