Anatomy of the Pterygopalatine Fossa
The pterygopalatine fossa is an inverted pyramidal-shaped, fat-filled space located on the lateral side of the skull, between the infratemporal fossa and the nasopharynx. It is known as a major neurovascular crossroad between the orbit, the nasal cavity, the nasopharynx, the oral cavity, the infratemporal fossa, and the cranial fossa. Given its inherent complex location and connections, the pterygopalatine fossa can act as a natural conduit for the spread of inflammatory and neoplastic diseases in the head and neck.
This article will focus on the skeletal framework and the contents of the pterygopalatine fossa, as well as how it serves as a gateway to other regions of the skull. Familiarizing yourself with the complex anatomy of the pterygopalatine fossa will give you a better understanding of its involvement in major pathological conditions.
The walls of the pterygopalatine fossa are formed by three bones of the skull:
The anterior wall is formed by the posterior surface of the maxilla. The medial wall is formed by the lateral surface of the palatine. The roof and the posterior wall are formed by the sphenoid, specifically the anterosuperior surface of its pterygoid process.
The pterygopalatine fossa houses many important neurovascular structures. Among these are the:
- maxillary nerve [V2]
- pterygopalatine ganglion
- terminal part of the maxillary artery
- veins, as well as their associated branches.
Maxillary Nerve [V2]
The maxillary nerve [V2] is purely sensory. It originates as the second division of the trigeminal ganglion in the cranial cavity, travels through the foramen rotundum, and enters the pterygopalatine fossa. At the pterygopalatine fossa, the maxillary nerve [V2] gives rise to the zygomatic nerve, the posterior superior alveolar nerve, and two ganglionic branches, while its main trunk continues into the inferior orbital fissure as the infraorbital nerve.
The ganglionic branches allow the maxillary nerve [V2] to communicate with the pterygopalatine ganglion, thus serving as a conduit for parasympathetic and sympathetic postganglionic fibers to travel through. Along with the sensory fibers of the maxillary nerve [V2], these fibers (sympathetic and parasympathetic) either leave directly from the pterygopalatine ganglion as orbital, palatine, nasal, and pharyngeal branches, or from the maxillary nerve [V2] along with its associated branches.
Collectively, the branches of the maxillary nerve and the pterygopalatine ganglion supply the:
- sphenoidal, ethmoidal and maxillary sinuses
- nasal cavity
- roof of the oral cavity
- upper teeth and their associated structures
- skin over the temple
- lower eyelid
- lateral aspect of the nose
- upper lip
The zygomatic nerve, being one branch of particular importance, carries parasympathetic postganglionic fibers from the pterygopalatine ganglion to supply the lacrimal gland.
The pterygopalatine ganglion is the largest of the four parasympathetic ganglia located in the head. At the pterygopalatine fossa, it sits inferior to the maxillary nerve [V2] and anterior to the opening of the pterygoid canal. The pterygopalatine ganglion houses the cell bodies of parasympathetic postganglionic neurons, and receives parasympathetic preganglionic fibers and sympathetic postganglionic fibers from the nerve of the pterygoid canal.
The nerve of the pterygoid canal is formed by the union of the greater petrosal nerve (branch of facial nerve [VII]) and the deep petrosal nerve (branch of carotid plexus); it thus carries parasympathetic preganglionic fibers of the greater petrosal nerve and sympathetic postganglionic fibers of the deep petrosal nerve. Once formed, the nerve of the pterygoid canal leaves the middle cranial fossa, travels through the pterygoid canal via the foramen lacerum, and enters the pterygopalatine fossa to join the pterygopalatine ganglion.
Note that only the parasympathetic preganglionic fibers of the nerve of the pterygoid canal synapse at the pterygopalatine ganglion, while the sympathetic postganglionic fibers travel through it. In addition, the maxillary nerve [V2] is purely sensory and thus has no autonomic function; however, it is used as a vehicle by parasympathetic and sympathetic fibers to reach their targets.
The maxillary artery is one of the major branches of the external carotid artery. It originates near the neck of the mandible, travels through the pterygomaxillary fissure via the infratemporal fossa, and enters the pterygopalatine fossa as the terminal part of the maxillary artery.
At the pterygopalatine fossa, it is located anterior to the pterygopalatine ganglion and gives rise to six branches that accompany the branches of the maxillary nerve [V2] and the pterygopalatine ganglion. These branches are the:
- posterior superior alveolar
- greater palatine
- artery of the pterygoid canal
Together, these branches supply the nasal cavity, the roof of the oral cavity, and all the upper teeth. They also contribute to the blood supply of the sinuses, the oropharynx, and the floor of the orbit.
Veins that drain the areas supplied by the branches of the terminal part of the maxillary artery travel with these branches back into the pterygopalatine fossa. They then continue through the pterygomaxillary fissure and join the pterygoid plexus in the infratemporal fossa.
The pterygopalatine fossa serves as a gateway for seven openings that communicate with the orbit, the nasal cavity, the oral cavity, the middle cranial fossa, and the infratemporal fossa. These openings transmit branches of the maxillary nerve [V2], the pterygopalatine ganglion, and the maxillary vessels. The seven openings are the:
- pterygomaxillary fissure
- foramen rotundum
- pterygoid canal
- palatovaginal canal
- inferior orbital fissure
- palatine canal
- sphenopalatine foramen
The pterygomaxillary fissure is located between the anterior and posterior wall of the pterygopalatine fossa. It communicates with the infratemporal fossa and transmits the posterior superior alveolar nerve and the maxillary artery.
The foramen rotundum is located on the posterior wall of the pterygopalatine fossa, superior to the pterygoid canal. It communicates with the middle cranial fossa and from there, it transmits the maxillary nerve [V2].
The pterygoid canal is located on the posterior wall of the pterygopalatine fossa, between the foramen rotundum and the palatine canal. It communicates with the middle cranial fossa and from there, it transmits the nerve, artery, and vein of the pterygoid canal.
The palatovaginal canal is located on the posterior wall of the pterygopalatine fossa, inferior to the pterygoid canal. It communicates with the nasal cavity and transmits the pharyngeal branches of the maxillary nerve and artery.
Inferior Orbital Fissure
The inferior orbital fissure is located on the superior border of the pterygopalatine fossa. It communicates with the orbit and transmits the zygomatic nerve and the infraorbital artery and vein.
The palatine canal is located inferiorly at the pterygopalatine fossa. It communicates with the oral cavity via the greater palatine and the lesser palatine canals, which transmit the greater palatine and lesser palatine nerves, respectively. The palatine canal also transmits the greater palatine artery.
The sphenopalatine foramen is located on the medial border of the pterygopalatine fossa. It communicates with the lateral wall of the nasal cavity and transmits nasal nerves and the sphenopalatine artery.
Because of its location and associated connections, the pterygopalatine fossa is often involved in the spread of tumours, infections, and inflammations caused by neoplastic diseases in the head and neck (such as juvenile nasopharyngeal angiofibroma, nasopharyngeal carcinoma, bacterial sinusitis, etc.).
For instance, in juvenile nasopharyngeal angiofibroma, the tumour extends into the pterygopalatine fossa via the sphenopalatine foramen, and spreads in a multidirectional fashion into other regions of the head, such as the sinuses, the infratemporal fossa, the orbit, and the cranial fossa.