THE PTERYGOPALATINE FOSSA.

Location and general description:

See the 3 images in the left pane to see the location of the pterygopalatine fossa.  All of these images can be viewed from the session II Gallery or as a Slide Show.

The pterygopalatine fossa is a small bony cavity shaped roughly like a funnel with its mouth facing upward against the base of the skull and its stem directed inferiorly, opening into the oral cavity through the greater palatine foramen.

The fossa lies below the base of the skull, behind the maxilla and in front of the pterygoid process of the sphenoid. When the skull is viewed from the front (norma frontalis) the pterygopalatine fossa lies just out of sight below the medial end of the inferior orbital fissure.

From a lateral view (norma lateralis) as seen in the figure on the left the fossa lies between the maxillary tuberosity anteriorly and the lateral pterygoid plate anteriorly.  The opening (or threshold) into the pterygopalatine fossa is called the pterygomaxillary fissure.  The fissure is a 2 dimensional landmark and can be thought of as a threshold or door jam.

In functional terms, the pterygopalatine fossa can be thought of as a utilities closet, from which electrical wiring (branches of the maxillary nerve) and plumbing (branches of part 3 of the maxillary artery and corresponding veins) are distributed to surrounding rooms (fossae).

Contents

Structures entering the fossa:

The maxillary division of the Trigeminal nerve (Cranial Nerve V) enters the fossa from the overlying middle cranial fossa through the foramen rotundum (red arrows). The maxillary artery enters from the infratemporal fossa through the pterygomaxillary fissure. Once in the fossa, nerve and artery break up unto their terminal branches, forming neurovascular bundles which radiate outward to their destinations.

The branches of the maxillary division distribute visceral nerve fibers which they receive from the pterygopalatine ganglion. Preganglionic parasympathetic fibers and taste fibers belonging to the Facial nerve (Cranial Nerve VII) reach the ganglion through the pterygoid (Vidian) canal. They are accompanied by postganglionic sympathetic fibers from the internal carotid plexus. The canal opens posteriorly at the base of the carotid groove on the body of the sphenoid, just in front of the petrous apex of the temporal bone. It passes forward in the base of the pterygoid process, immediately below the floor of the sphenoid air sinus, and enters the pterygopalatine fossa below and medial to the foramen rotundum.

Structures leaving the fossa:

Preganglionic parasympathetic fibers synapse on cells of the pterygopalatine ganglion; postganglionic sympathetics and taste afferents do not. Visceral nerve fibers leave the ganglion to enter appropriate branches of the maxillary nerve.

Infraorbital and zygomatic nerves leave the fossa anteriorly via the inferior orbital fissure.

Greater and lesser palatine nerves descend through the greater palatine canal and its smaller offshoots to reach the greater and lesser palatine foramina on the under surface of the hard palate.

Posterior superior nasal nerves and the sphenopalatine artery pass medially through the sphenopalatine foramen to enter the nasal cavity.

Posterior superior alveolar nerves and vessels pass laterally through the pterygomaxillary fissure into the infratemporal fossa. They enter small posterior superior alveolar foramina on the rounded surface of the maxilla above the upper rear molars.

Pharyngeal nerves and vessels exit the fossa posteromedially through the palatovaginal canal, which lies between the upper border of the palatine bone and the vaginal process of the sphenoid. This small neurovascular bundle is distributed to the upper reaches of the pharyngeal wall just behind the entrance of the auditory tube.

Relationships with other spaces

The pterygopalatine fossa lies below and behind the apex of the orbit. It is situated:

Communications with other spaces

Superiorly, the pterygopalatine fossa communicates with the middle cranial fossa through foramen rotundum.

Posteriorly, it communicates with cranial entrance of the carotid canal by means of the pterygoid (Vidian) canal, a 2-3 cm long horizontal passageway in the thickness of the sphenoid bone, above the pterygoid process and below the floor of the sphenoid air sinus.

It also communicates with the upper and posterior part of the nasopharynx through the palatovaginal canal. This small passageway lies below the sphenoid bone, between it and the upper edge of the vertical plate of the palatine bone. Its pharyngeal opening can be found between the vaginal process of the sphenoid and the palatine.

Anteriorly, the pterygopalatine fossa opens into the floor of the orbit through the inferior orbital fissure.

Laterally, it communicates with the infratemporal fossa through the pterygomaxillary fissure, which can be thought of as an open doorway framed by the margin of the pterygoid process of the sphenoid and the tuberosity of the maxilla.

Medially, the pterygopalatine fossa opens into the nasal cavity through the sphenopalatine foramen.

Inferiorly, the fossa communicates with the oral cavity by means of the greater and lesser palatine canals, which terminate in corresponding foramina on the under (oral) surface of the hard palate.

Parieties

Roof: The roof of the pterygopalatine fossa is formed by the sphenoid bone at the union between the body and the greater wing. The roof is pierced by the foramen rotundum, really a short oblique tunnel directed downward and forward through the floor of the middle cranial fossa.  The foramen rotundum transmits the maxillary division of the Trigeminal nerve.

Anterior wall: The anterior wall of the pterygopalatine fossa is formed by the tuberosity of the maxilla, the rear wall of the maxillary sinus. The bone here is uninterrupted by the passage of notable nerves or vessels. It is very thin, however, and easily eroded by tumors arising from the lining of the sinus. It also permits (potential?) surgical access to the fossa through the sinus.

The maxilla never rises high enough to meet the sphenoid, leaving a linear gap – the inferior orbital fissure – between them. The fissure intersects the upper reach of the pterygomaxillary fissure and extends back into the pterygopalatine fossa. Therefore, it provides a pathway linking the pterygopalatine fossa with the infratemporal fossa and the floor of the orbit.


The maxillary nerve exits the pterygopalatine fossa through the superior orbital fissure. It appears briefly high in the infratemporal fossa and immediately enters the orbit as the infraorbital nerve. The fissure also transmits the zygomatic nerve, the infraorbital and zygomatic arteries, and corresponding veins. The nerve arises from the maxillary nerve in the pterygopalatine fossa. The arteries are branches of part three of the maxillary artery, and the veins are tributaries to the pterygoid venous plexus.

Lateral wall: The pterygopalatine fossa has no lateral wall. Instead, it opens freely into the infratemporal fossa through the pterygomaxillary fissure. The fissure is best likened to a doorframe made up of the infratemporal crest of the sphenoid (above), the anterolateral margin of the pterygoid process of the sphenoid (posteriorly) and the surface of the maxilla (anteriorly). Although the pterygoid process slopes downward and forward toward the maxilla, the two elements never meet. The pyramidal process of the palatine bone intervenes between them to close the fissure inferiorly.
The pterygomaxillary fissure transmits:

Posterior wall: The posterior wall of the fossa consists of the smooth, planar anterior surface of the pterygoid process of the sphenoid, which slopes downward and forward toward the maxilla.

On horizontal section, the pterygoid process is U-shaped. The limbs of the U consist of the thin lateral and medial pterygoid plates, which project posteriorly from the central element of the process. The U itself forms [defines? encloses?] the pterygoid fossa, containing the medial pterygoid and tensor veli palatini muscles. Despite their close proximity, there is no direct communication between pterygoid and pterygopalatine fossae.

The posterior wall of the pterygopalatine fossa presents two openings, one small and one large. The smaller aperture, in the angle between roof, posterior wall and medial wall, is that of the palatovaginal canal. It is described with the medial wall. The much larger opening is that of the pterygoid canal.

The pterygoid, or Vidian, canal opens into the rear wall of the pterygopalatine fossa, well below and medial to the entrance of the foramen rotundum. The canal leads posteriorly away from the fossa into the sphenoid bone, where it runs through the base of the pterygoid process and below the floor of the sphenoidal air sinus. In some individuals, the canal is roofed only by the lining of the sinus. Posteriorly, the canal opens at the base of the carotid groove on the body of the sphenoid, immediately in front of the internal carotid artery as it emerges from the apex of the petrous temporal bone onto the upper surface of the cartilage that fills the foramen lacerum in life.

The canal is occupied by the nerve of the pterygoid canal (Vidian nerve) and by the artery of the pterygoid canal. The nerve is a composite of the greater petrosal nerve, a branch of the Facial nerve, and the deep petrosal nerve from the internal carotid sympathetic plexus. The artery is an anastomotic channel between the external carotid (maxillary artery) and internal carotid systems. The corresponding channel drains into the pterygoid venous plexus and the cavernous sinus. [Check to make sure, or eliminate.]
 

Medial wall: The medial wall of the pterygopalatine fossa is more difficult to visualize than the other boundaries. It is formed by the vertical plate of the palatine bone, which separates the fossa from the nasal cavity.

The palatine bone consists of two flat plates, one horizontal the other vertical, that meet at right angles, and a pyramidal process arising posteriorly from the union of the plates. [Ref. to picture(s) of an isolated palatine and at the same time to pictures of the hard palate and lateral nasal wall in situ, appropriately color coded or shaded to emphasize the points made in the text.]

The horizontal plate forms the posterior third of the hard palate.

The vertical, or perpendicular plate, forms a corresponding section of the lateral nasal wall, immediately in front of the medial pterygoid plate. The perpendicular plate rises to meet the body of the sphenoid and the ala (wing) of the vomer.

Anteriorly, it articulates with the nasal surface of the maxilla and helps complete the medial wall of the maxillary sinus.

Posteriorly, it forms the medial wall of the pterygopalatine fossa.

The upper margin of the vertical plate is sculpted deeply into a sphenoidal notch framed by the orbital and sphenoidal processes of the palatine bone.

The anterior, orbital process, as its name implies, contributes to the floor of the orbit where it forms the anterior lip of the base of the inferior orbital fissure. [picture of orbit]

The posterior, sphenoidal process, is applied against the undersurface of the body of the sphenoid and flares medially to contact the edge of the ala of the vomer.

The palatovaginal canal lies between the sphenoidal process and the overlying base of the skull, linking the pterygopalatine fossa with the nasopharynx. Anteriorly it opens high on the rear wall of the fossa, in the angle between the roof and the medial wall. Its posterior entrance lies between the rear edge of the sphenoidal process of the palatine and the vaginal process of the sphenoid.

Occasionally a subsidiary vomerovaginal canal is formed between the ala of the vomer and the vaginal process, linking the nasopharynx with the palatovaginal canal. Palatovaginal and vomerovaginal canals both allow passage of small pharyngeal nerves and vessels.

The nerves are branches of the maxillary division of the Trigeminal through the pterygopalatine ganglion. The arteries are derived from part three of the maxillary artery, and the veins drain to the pterygoid venous plexus.

The sphenoidal notch of the palatine faces a much shallower palatine notch of the sphenoid bone. Together, the two notches frame the sphenopalatine foramen linking the pterygopalatine fossa with the nasal cavity. The foramen transmits the posterior superior nasal nerves and the sphenopalatine artery from the pterygopalatine fossa into the nasal cavity.

The nerves are branches of the maxillary division of the Trigeminal. The artery is the main-line terminal branch of the third part of the maxillary artery. Corresponding veins pass back through the foramen into the pterygopalatine fossa on their way to join the pterygoid venous plexus in the infratemporal fossa.

Floor: The pterygopalatine fossa has no clearly recognizable floor. Instead, it narrows gradually as its rear wall, the pterygoid process, approaches the maxilla. It then becomes continuous with the:

The nerves are branches of the maxillary division of the Trigeminal, although they often are described as branches of the pterygopalatine ganglion. The arteries usually originate from the descending palatine artery in the greater palatine canal. The veins drain upward through the lesser and greater palatine canals into the pterygopalatine fossa on their way to the pterygoid venous plexus.