Pterygoid Plexus
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Direct answer
Veins of the deep face gather into the pterygoid plexus, a dense valveless network woven around and between the lateral and medial pterygoid muscles in the infratemporal fossa. It collects the middle meningeal, deep temporal, pterygoid, masseteric, buccal, dental, greater palatine, pharyngeal and infraorbital veins, drains mainly through the maxillary veins into the retromandibular vein, and connects in three dangerous directions: with the facial vein through the deep facial vein, with the inferior ophthalmic vein through the inferior orbital fissure, and — the examinable crown — with the cavernous sinus through emissary veins traversing the foramen ovale, the sphenoidal emissary foramen of Vesalius and adjacent skull-base openings. Because the plexus is valveless, flow follows pressure, which is why infections of the upper molars, the tonsil or the face can travel backwards into the cavernous sinus.
What you must remember
- Position and extent: infratemporal fossa, around the lateral pterygoid and between the two pterygoids, extending up to the inferior orbital fissure — the plexus is both a venous net and a cushion around the pterygoid muscles.
- Tributaries worth naming: middle meningeal vein (also draining the meninges), deep temporal veins, dental and alveolar veins from upper and lower teeth, buccal, masseteric, pterygoid, greater palatine, pharyngeal and infraorbital veins.
- Drainage: maxillary veins (often paired) run back between the sphenomandibular ligament and the mandible to join the superficial temporal vein, forming the retromandibular vein.
- Cavernous connections: emissary veins through the foramen ovale and the sphenoidal emissary foramen (of Vesalius) plus connections with the inferior ophthalmic vein via the inferior orbital fissure — all valveless, all bidirectional.
- Danger area of the face: the facial vein lacks valves and anastomoses at the inner canthus with the superior ophthalmic vein; deep face infection reaches the plexus through the deep facial vein — squeezing a boil on the upper lip or nose is the classical precipitant.
- Cavernous sinus thrombosis picture: periorbital oedema and chemosis, proptosis, ophthalmoplegia (III, IV, VI), V1 and V2 sensory loss, papilloedema with high fever — and possible spread across intercavernous sinuses to the opposite eye.
- Everyday dental relevance: a posterior superior alveolar or inferior alveolar injection can puncture the plexus, producing an immediate expanding haematoma of the cheek; pressure and cold compress manage most.
From an infected molar to the cavernous sinus
A young man neglects an infected upper second molar for a week; the periorbital swelling begins on the third day of facial pain. The route is written in this plexus. Dental veins from the maxillary roots drain directly into the plexus; thrombophlebitic clot then climbs the emissary veins through the foramen ovale — or rides the inferior ophthalmic vein — into the cavernous sinus. Within days the full syndrome declares itself: brawny lid oedema, chemosis, proptosis, paralysed ocular movements as the third, fourth and sixth nerves in the sinus wall are engulfed, hyperaesthesia or anaesthesia in V1 and V2, and a toxic, febrile patient. High-dose intravenous antibiotics (with anaerobic cover from the oral source) have transformed a historically fatal condition, but the lesson stands: no facial abscess in the danger zone should be squeezed.
Where students slip
Two confusions dominate practical examinations. First, the plexus is equated with the cavernous sinus itself — it is not; it is an extracranial network connected to the sinus by emissary veins, and the distinction explains why dental infections cause intracranial thrombosis without any "direct extension". Second, candidates forget the maxillary vein as the plexus's main outflow and instead invent drainage into the facial vein; the deep facial vein is a connection, not the trunk. A polished answer also names the sphenoidal emissary foramen (of Vesalius) — the small foramen medial to the foramen ovale transmitting its own emissary vein — a structure textbooks mention only here, and whose name is worth a viva half-mark.
Frequently asked questions
Where exactly is the pterygoid plexus located?
In the infratemporal fossa, around the lateral pterygoid muscle and between the lateral and medial pterygoids, extending up to the inferior orbital fissure.
How does the pterygoid plexus communicate with the cavernous sinus?
Through valveless emissary veins passing via the foramen ovale and the sphenoidal emissary foramen of Vesalius, and indirectly through the inferior ophthalmic vein at the inferior orbital fissure.
Why is the upper part of the face called the danger area?
Its veins — the valveless facial vein and the deep facial vein — connect the skin of the lips and nose to the pterygoid plexus and ophthalmic veins, so infection can propagate to the cavernous sinus.
What clinical event follows pterygoid plexus puncture during dental anaesthesia?
Rapid formation of a cheek haematoma after posterior superior alveolar or inferior alveolar nerve injections, managed with immediate firm pressure and cold compresses.
Name the classic signs of cavernous sinus thrombosis.
Periorbital oedema, chemosis, proptosis, ophthalmoplegia of the third, fourth and sixth nerves, V1–V2 sensory impairment and papilloedema, often with high fever — sometimes spreading to both eyes.